<pubnumber>22P-2001</pubnumber>
<title>Cooling Our Communities Guidebook On Tree Planting And Light-colored Surfacing</title>
<pages>243</pages>
<pubyear>1992</pubyear>
<provider>NEPIS</provider>
<access>online</access>
<operator>LAI</operator>
<scandate>20060719</scandate>
<origin>hardcopy</origin>
<type>single page tiff</type>
<keyword>trees tree planting urban energy colored cooling heat light water surfacing albedo city guidebook temperatures ordinance communities cities landscape shade</keyword>
United States
Environmental Protection
Agency
Policy, Planning
And Evaluation
(PM-221)
22P-2001
January 1992
EPA Cooling Our Communities
EPRI
Electric Power
Research Institute
A Guidebook On Tree Planting
And Light-Colored Surfacing
Printed on Recycled Paper
image:
USB
\ UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
OFFICE OF
POLICY. PLANNING AND EVALUATION
January 2, 1992
I am proud to introduce our new publication, Cooling Our Communities: A Guidebook on Tree
Planting and Light-Colored Surfacing. This book is a practical guide that presents the current state of
knowledge on potential environmental and economic benefits of strategic landscaping and altering surface
colors in our communities. The guidebook, a joint effort of the Environmental Protection Agency and the
Department of Energy's Lawrence Berkeley Laboratory, reviews the causes, magnitude, and impacts of
increased urban warming, then focuses on actions by citizens and communities that can be undertaken to
improve the quality of our homes and towns in cost-effective ways.
Summer temperatures in urban areas are now typically 2°F to 8°F higher than in their rural
surroundings, due to a phenomenon known as the "heat island effect." Research shows that increases in
electricity demand, smog levels, -and human discomfort are probably linked to this phenomenon. Planting
trees to provide shade and protection from winter winds, and lightening the color of building and
pavement surfaces have the potential to significantly reduce energy use for cooling, and lower electrical
bills. The guidebook shows that well-placed vegetation around residences and small commercial buildings
can reduce energy consumption typically by 15 to 35 percent. Savings from lightening surface colors may
be as high or greater, but are still being quantified. Widespread adoption of these strategies could help
reduce urban temperatures and smog.
* * *
We designed the Cooling Our Communities guidebook with several general audiences in mind.
Following are suggestions for ways each audience can apply the guidebook's findings and
recommendations. The document also includes many technical appendices for the benefit of city planners,
urban foresters, and electrical utilities needing more specific information about these principles.
Elected officials and other policymakers: The principles in this book have great potential to reduce
expenditures for building energy, build citizen support for government tree planting programs, and improve
the lives of our citizens. We hope you will actively support the types of activities and programs
recommended here by sharing the guidebook with your staff and constituents, and consider launching
volunteer or public/private partnership programs to implement these principles.
Foresters, landscapers, architects, and urban planners: Citizens are increasingly demanding these
changes in their communities and are willing to volunteer time and resources to bring them about. You
can support and encourage their efforts by using the guidebook to incorporate these approaches into your
professional practice.
Utilities: Many power companies have already established tree planting programs to foster energy
conservatioa Major opportunities exist for utilities to cooperate with citizens, homeowners, and
communities to expand the use of these recommended strategies.
Commercial interests: Demand is increasing for products and services that save people money and
energy. We hope that retailers, manufacturers, and contractors of products and services involving
Printed on Recycled Paper
image:
vegetation, buildings and pavements will incorporate these energy saving ideas into their product and
service lines, and advise consumers fully about the potential benefits of using them. Developers may
increase the value of their properties by including these principles in their designs.
Citizen's and community groups: The successes and experiences of many of your colleagues across the
entire United States are reflected in this book. Join them by taking action in your own communities to
organize tree planting and light-colored surfacing projects.
Professional schools and programs: Community professionals can be the most effective supporters of
improving environmental quality. Incorporating these design principles into your programs will help
professionals in your disciplines understand and use these principles.
Editors, publication managers, and public affairs staff: To expedite informing your colleagues about
the guidebook and its availability, we suggest you review or abstract the document in your in-house
publications. We have included a sample abstract and order forms at the back of the book for you to copy
and use as you wish.
* * *
Innumerable citizen groups and municipalities have clearly demonstrated the will to band together
and plant trees in the United States. The guidebook supports these efforts, and identifies light-colored
surfacing as a strategy that may have similar benefits. Now the challenge is to guide this volunteer spirit
to achieve measureable environmental improvements in all of our communities. This publication is one
of EPA's contributions to this on-going movement.
Rkhard D. Morgenstern
Acting Assistant Administrator
image:
Cooling Our Communities
A Guidebook on Tree Planting and
Light-Colored Surfacing
Editors:
Hashem Akbari, Lawrence Berkeley Laboratory
Susan Davis, Lawrence Berkeley Laboratory
Sofia Dorsano, The Bruce Company
Joe Huang, Lawrence Berkeley Laboratory
Steven Winnett, U.S. Environmental Protection Agency
U.S. Environmental Protection Agency
Office of Policy Analysis
Climate Change Division
January 1992
image:
This document has been reviewed in accordance with the U.S. Environmental Protection Agency's
and the Office of Management and Budget's peer and administrative review policies and approved
for publication. Mention of trade names or commercial products does not constitute endorsement
or recommendation for use.
Publisher's Note:
This is Lawrence Berkeley Laboratory Report LBL-31587.
This work was supported by the U.S. Department of Energy under contract No. DE-AC0376SF00098.
Those who wish to order the Guidebook should inquire at the address below:
Publications Requests:
GPO Document #055-000-00371-8
Superintendent of Documents
P.O. Box 371954
Pittsburgh, PA 15220-7954
ATTN: New Orders
For sale by the U S Government Printing Office
Supenntendent of Documents, Mail Stop- SSOP, Washington, DC 20402-9328
ISBN 0-16-036034-X
image:
Cooling Our Communities
A Guidebook on Tree Planting and
Light-Colored Surfacing
Editors:
Hashem Akbari, Lawrence Berkeley Laboratory
Susan Davis, Lawrence Berkeley Laboratory
Sofia Dorsano, The Bruce Company
Joe Huang, Lawrence Berkeley Laboratory
Steven Winnett, U.S. Environmental Protection Agency
Project Directors: Principal Investigator:
Joe Huang, LBL Hashem Akbari, LBL
Steven Winnett, U.S. EPA
Kenneth Andrasko, U.S. EPA
SPONSORS:
U.S. Environmental Protection Agency
Heat-Island Project at Lawrence Berkeley Laboratory,
University of California
U.S. Department of Energy
California Institute for Energy Efficiency
Los Angeles Department of Water and Power
Universitywide Energy Research Group, University of California
Electric Power Research Institute
American Council for an Energy Efficient Economy
U.S. Environmental Protection Agency Lawrence Berkeley Laboratory
Office of Policy Analysis Energy Analysis Program
Climate Change Division Energy & Environment Division
401 M Street, SW (PM-221) 1 Cyclotron Rd.
Washington, D.C. 20460 Berkeley, CA 94720
(202)260-8825 (510)486-4000
image:
Contents
Foreword by William K. Reilly xiii
Acknowledgements xv
Executive Summary xvii
Introduction 1
Chapter
1 The Urban Heat Island: Causes and Impacts 5
2 The Benefits of Urban Trees 27
3 Using Light-Colored Surfaces to Cool Our Communities 43
4 Implementation Issues: Water Use, Landfills, and Smog 53
5 Lessons Learned from Successful Tree Programs 63
6 Planting and Light-Colored Surfacing for Energy Conservation 93
7 Ordinances HI
8 Conclusions and Recommendations 129
References 139
Appendix
A Further Data on Heat Islands 151
B The Costs of Conserved Energy 153
C Estimating Water Use by Various Landscape Scenarios 157
D Sample Ordinance 173
E The Best Way to Plant Trees 195
F Trees and Shrubs 201
G Sample Tree Planting Incentive Program 211
H Planting New Life in the City Down the Street 213
VII
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Graphs
ES-2 Urban areas are getting warmer xix
ES-3 Rising temperatures and smog xix
ES-6 Energy savings from residential tree planting xxi
ES-7 Computer simulation of both wind-shielding and shading effects xxii
ES-8 Daily surface temperatures xxiii
ES-9 Cooling energy savings from increased albedo xxiii
ES-10 Costs and benefits of community trees xxv
1-8 Maximum difference in urban and rural temperatures 12
1-9 Los Angeles (CA) heat record 13
1-10 San Francisco (CA) heat record 13
1-11 Washington, D.C. temperatures 14
1-12 Fort Lauderdale (FL) temperatures 14
1-13 Shanghai (China) temperatures 15
1-14 Tokyo (Japan) temperatures 15
1-15 California heat islands 16
1-16 Shanghai heat island 16
1-18 Electricity load—Los Angeles Department of Water and Power (LADWP) 18
1-19 Electricity load—Southern California Edison (SCE) 18
1-20 Electricity records for four cities—
Dallas, Colorado Springs, Phoenix, and Tucson 19
1-21 Estimated temperature increases in the United States 20
1-22 Estimated electricity increases in the United States 20
1-23 Ozone concentrations compared to daily peak temperatures
in downtown Los Angeles (CA) 21
1-24 Ozone concentrations compared to daily peak temperatures
in 13 cities in Texas 21
2-3 Effects of shading from a 30 percent increase in tree cover on the heating
and cooling energy use of older houses, based on computer simulation 30
2-4 Wind speed reductions in residential neighborhoods
compared to an open field 30
2-5 Effects of wind shielding from a 30 percent increase in tree cover on the heating
and cooling energy use of older houses, based on computer simulation 31
2-6 Net direct effects of both wind shielding and shading from a 30 percent increase
in tree cover on the heating and cooling energy use of older houses,
based on computer simulation 31
2-7 Temperature reductions in Sacramento (CA) due to added tree cover on a
typical summer day in July, based on computer simulation 33
VIII
image:
Contents
2-8 Temperature reductions in Phoenix (AZ) due to added tree cover on a
typical summer day in July, based on computer simulation 33
2-9 Estimated cooling energy savings in a typical well-insulated, new house
from the combined direct and indirect effects of trees 34
2-13 Projected annual costs and benefits of the Trees
for Tucson/Global ReLeaf reforestation program 41
3-4 Effects of surface color on temperature 46
3-5 Year-round ground surface temperatures 47
3-6 Cooling energy savings from increased albedo 48
5-1 Summary report (National Street Tree Survey) 63
5-2 Street construction dollar (National Street Tree Survey) 70
5-3 Breakdown of costs involved in city tree planting programs
(National Street Tree Survey) 72
5-4 Percentage of trees in good condition (National Street Tree Survey) 77
5-5 Tree size distribution (National Street Tree Survey) 77
6-6 Comparison of tree longevity relative to location 96
8-1 Three scenarios of future Los Angeles temperatures,
added to a forecast of global warming trend 130
A-l Heat record for Oakland (CA) 151
A-2 Heat record for San Jose (CA) 152
A-3 Heat record for San Diego (CA) 152
A-4 Heat record for Sacramento (CA) 152
A-5 Heat record for Baltimore (MD) 152
Illustrations
ES-l Sketch of a typical urban heat-island profile xvii
ES-4 Sample residential landscape xx
ES-5 Strategic planting example xxi
ES-11 Strategic tree planting and light-colored surfacing activities xxvi
1-1 Comfort in the shade and moist air 5
1-4 Sketch of a typical urban heat-island profile 9
1-25 The greenhouse effect 23
1-26 Electricity use and carbon dioxide (CO2) emissions 24
2-1 The numerous ecological qualities of trees 27
2-2 Shading characteristics of deciduous trees during the summer and winter 29
2-10 Trees and the greenhouse effect 35
2-11 Benefits of berm 37
IX
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
2-12 Aesthetic value of trees 38
2-14 Consider the seasonal path of the sun
when planning landscaping improvements 42
3-2 Surface contrast 44
3-3 Surface albedo values 45
4-1 Relative water usage of different types of plants 56
4-2 Water consumption and turf 56
6-2 Sample guidelines for planning tree planting 94
6-3 Avoid planting trees right next to drainage pipes 95
6-4 Trees need to be placed a good distance away from concrete sidewalks 95
6-5 Improper tree planting 96
6-7 Shading the air conditioner with a vine-covered trellis or trees can
provide enough shade to make a noticeable difference in temperature 97
6-8 Vines provide shade and evapotranspiration benefits 97
6-9 Sample residential landscape 99
6-10 Strategic planting diagram 99
6-11 Solar path diagram 100
6-12 Trees channel breezes 101
6-13 Plant lines and plant forms , 102
6-14 Change of shade patterns on daily and seasonal basis 103
6-15 Parking lots without vegetation for shading are extremely vulnerable
to the penetrating solar heat 105
6-16 Trees planted throughout a parking lot are far more effective "coolers"
than those planted around the edges only 105
7-1 Ordinances set standards for minimal level of performance 114
7-2 Flexibility may be one of the most appealing features of a good ordinance 116
7-3 The effectiveness of ordinances may be assisted by
generating enthusiasm to co-participate 117
7-4 The public needs access to information that clearly explains
compliance criteria and standards 125
7-5 Trees require systematic care and watering in order to reach maturity 126
7-6 Community input in the planning stages of ordinances is invaluable
to both the community and the administering agency 127
8-2 Planning room for trees 135
8-3 The value of incentives 136
F-l Proper support for newly planted trees 202
F-2 Diagram of species classified by climate zone 203
F-3 Seasonal sun angles and day length 210
image:
Contents
Maps
1-5 Winter heat island in London, England 10
1-6 Winter heat island in Montreal, Canada 10
1-7 Heat-island profile of downtown St. Louis, Missouri 11
1-17 Map of climate regions based on heating and cooling requirements 17
Photographs
1-2 Rural building (and air conditioner) shaded by trees 6
1-3 Urban canyons block breezes 8
3-1 Traditional light surfaces 43
3-7 Residents of cities in tropical and mediterranean areas have white-washed
their buildings for centuries, sometimes repainting outside walls annually
to ensure comfort 50
6-1 Trees on city streets 93
6-17 On Pennsylvania Avenue in downtown Washington, D.C., pedestrians
enjoy a changing landscape featuring boulevards lined with trees 106
8-4 Thinking about the future 137
E-l Gary Moll (American Forestry Association) with balled-root planting stock 195
Tables
1-1 Measured temperature trends in selected cities 15
1-2 Correlation between temperatures and electricity demand for selected
utility districts based on measured data for 1986 19
C-l Monthly and averaged crop coefficients for selected plants 161
C-2 Average summertime crop coefficients for landscape vegetation classes 161
C-3 Estimated crop coefficients of 150 landscape plants based on
annual precipitation in their native habitats 163
C-4 Calculated changes in plant ET requirements for different
landscape scenarios based on crop coefficients in Table C-B 168
C-5 Calculated changes in plant ET requirements for different
landscape scenarios based on crop coefficients for low-water-use vegetation 169
D-l Tree credit system—1 190
D-2 Tree credit system—2 191
D-3 Credit for hours air conditioner is shaded 191
D-4 Shrub credit system 191
D-5 Example calculations of landscaping requirements utilizing credit system 193
G-l Tree selection chart 212
XI
image:
Foreword
In the 1990 State of the Union address to the U.S. Congress, President Bush unveiled
his America the Beautiful Tree Planting Program, one of the most ambitious
anywhere in the world. Its goals are to plant one billion trees each year and improve
forest management on targeted lands. This new EPA publication, Cooling Our Com-
munities, focuses on one element of that program, community tree planting, and adds
a new component, light-colored surfacing. It describes how citizens can help reduce
air pollution, abate the greenhouse gas carbon dioxide, and potentially lower rising
urban temperatures through two types of activities—planting trees around homes
and other small buildings, and lightening the color of buildings and paved surfaces.
Each can save energy, reaping environmental and economic benefits. This guidebook
shows how the efforts of volunteers, spurred by growing environmental awareness,
can be tapped to improve our communities.
My appreciation goes to the Department of Energy's Lawrence Berkeley Labo-
ratory, which worked with EPA on this guidebook. It draws on the expertise of
specialists in government, universities, and other organizations, and the experiences
of many individuals. Many thanks to all who contributed to producing this report.
As President Bush announced the America the Beautiful program, he said, "Every
tree is a compact between generations." I hope the findings and recommendations
in this document provide the impetus for individuals and for members of private groups
to plant trees for our common good, and for that of generations to come.
January, 1992
XIII
image:
Acknowledgements
This guidebook was completed as a special project by the Climate Change Division
of the U.S. Environmental Protection Agency (EPA), and the Energy Analysis
Program of Lawrence Berkeley Laboratory (LBL). The project's Principal Investigator
is Hashem Akbari of LBL. The Project Directors are Steven Winnett and Kenneth
Andrasko of EPA, and Joe Huang of LBL.
The guidebook represents the cumulative work of many people extending over
two years. We would like to give special recognition to Arthur Rosenfeld at LBL
and Kenneth Andrasko at EPA for the initial concept of producing a "heat island miti-
gation handbook," and then developing the original guidebook outline.
In addition to EPA and LBL, this project was also sponsored by the following
organizations: the U.S. Department of Energy (DOE), the California Institute of Energy
Efficiency (CIEE), Los Angeles Department of Water and Power (LADWP), the
Universitywide Energy Research Group of the University of California (UERG), the
Electric Power Research Institute (EPRI), and the American Council for an Energy
Efficient Economy (ACEEE).
We wish to thank Peter Beedlow, Bruce Schillo, Gordon M. Heisler, Margot
W. Garcia, Neil Sampson, Gary Moll, George Britton, James Demetrops, and Linda
J. de la Croix for providing formal reviews of the guidebook. We also thank the
numerous reviewers of the guidebook drafts, Gordon Binder, Dan Esty, Richard
Morgenstern, Courtney Riordan, Edgar Thorton, Dennis Tirpak, Jane Leggett, Gregory
McPherson, Timothy Oke, John Parker, Judy Ratcliffe, Allen McReynolds, and
Marcia Bansley. In addition, the authors of the individual chapters also contrib-
uted in reviewing various drafts.
For their graphics, editorial, and other bookmaking contributions, we extend our
appreciation to the staff of The Bruce Company presentations division, especially
Allison Anderson, Paula Batchelor, Paul Jordan, Todd Neitring, Shelley Preston,
Jeffrey Satterwhite, and Mildred Stewart.
The following people authored this report:
Akbari, Hashem. Energy & Environment Division, Lawrence Berkeley Laboratory,
University of California, Berkeley. (Chapter 1; Chapter 3)
Arey, Janet. Statewide Air Pollution Research Center, University of California,
Riverside. (Chapter 4)
XV
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Cooling Our Communities
The Guidebook on Tree Planting and Light-Colored Surfacing
Atkinson, Roger. Statewide Air Pollution Research Center, University of California,
Riverside. (Chapter 4)
Carhart, Ralph. California Department of Transportation, Sacramento. (Chapter 8)
Davis, Susan E. San Francisco, California. (Chapter 1; Chapter 6)
Garbesi, Karina. Energy & Environment Division, Lawrence Berkeley Laboratory,
University of California, Berkeley. (Chapter 4; Appendix C)
Huang, Joe. Energy & Environment Division, Lawrence Berkeley Laboratory,
University of California, Berkeley. (Chapter 1; Chapter 2)
Lipkis, Andy. TreePeople, Inc., USA of Los Angeles, CA. (Chapter 5)
Lipkis, Katie. TreePeople, Inc., USA of Los Angeles, CA. (Chapter 5)
Liu, Phillip. University of California, Davis. (Chapter 1)
Martien, Philip. Bay Area Air Quality Management District, San Francisco, CA.
(Chapter 3; Chapter 6)
McPherson, E. Gregory. USDA Forest Service. Chicago, IL. (Chapter 5)
Moll, Gary. American Forestry Association. Washington, D.C. (Appendix E)
Nordman, Bruce. Energy & Environment Division, Lawrence Berkeley Laboratory,
University of California, Berkeley. (Chapter 4)
Panzer, Susan. Florida International University, Miami. (Appendix D)
Patterson, Fred. Energy & Environment Division, Lawrence Berkeley Laboratory,
University of California, Berkeley. (Chapter 7)
Parker, John. Florida International University, Miami. (Appendix D)
Ratliffe, Judy. University of Arizona, Tucson. (Chapter 5)
Ritschard, Ron. Applied Sciences Division, Lawrence Berkeley Laboratory, University
of California, Berkeley. (Chapter 2)
Rosenfeld, Arthur. Energy & Environment Division, Lawrence Berkeley Laboratory,
University of California, Berkeley. (Chapter 3)
Sampson, Neil. American Forestry Association, Washington, D.C. (Chapter 2;
Chapter 6)
Taha, Haider. Energy & Environment Division, Lawrence Berkeley Laboratory,
University of California, Berkeley. (Chapter 2)
XVI
image:
Executive Summary
Summer temperatures in urban areas are now typically 2°F to 8°F higher than in
their rural surroundings, due to a phenomenon known as the "heat island effect."
Recent research shows that increases in electricity demand, smog levels, and human
discomfort are probably linked to this phenomenon.
Urban areas accumulate greater amounts of heat for several reasons. Many of
these factors—including climate, topography, and weather patterns—cannot be
changed. Two factors we can influence are the amount of vegetation and-the
color of surfaces. These two factors are responsible for the majority of additional
heating attributable to human activities.
Strategically planting trees and lightening building and pavement surface colors
have the potential to reduce energy use for cooling and lower electrical bills. This
may also help lower summer temperatures in our communities, thereby reducing the
production of tropospheric ozone and improving the quality of our environment. By
reducing the generation of electrical power, these actions also decrease the emission
of carbon dioxide (CO2), the most important greenhouse gas, and may help lower
the risk of global climate change.
Initial analysis suggests that billions of dollars may be spent each year just to
compensate for the increased heat of an urban heat island. Planting trees and lightening
Sketch of an Urban Heat-Island Profile
92°
I
i
85°-
.••""••.
•••.......••• \
•4
*•••••••••
Rural Suburban Commercial Downtown Urban Park Suburban Rural
Residential Residential Residential Farmland
Figure ES-1.
Sketch of a typical urban
heat-island profile- This
graph of the heat island
profile in a hypothetical
metropolitan area shows
temperature changes
(given in degrees Fahren-
heit) correlated to the
density of development
and trees. (Also appears
as Figure 1-4.)
Source Andrasko, Huang, 1990
XVII
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Peak tempera-
tures in Los
Angeles, other
cities of north-
ern California,
Texas, Washing-
ton, D.C.,
Shanghai, and
Mexico City
show that peak
temperatures
have risen
throughout the
century.
the color of our urban surfaces could lower our urban temperatures, reduce our cooling
energy use, and lower smog levels. A study by the National Academy of Sciences
indicates that these strategies may be able to save 50 billion kilowatt hours, or 25
percent, of the 200 billion kilowatt hours spent annually in the United States for air
conditioning (NAS, 1991). Programs that encourage these energy-saving practices
could also beautify urban areas, mask noise, reduce air pollution, enhance community
relations, and provide valuable habitat for wildlife.
This guidebook is designed to introduce both lay and technical readers to the
potential of tree planting and light-colored surfacing methods for reducing energy
demand and lowering urban temperatures. It is the first collection of such material.
Therefore, its findings and recommendations should be considered a foundation for
future inquiry and work, and not a final analysis.
Why Are Urban Temperatures Rising?
The urbanization of the natural landscape—roads, bridges, dams, houses, and high-
rises—has dramatically altered its waters, soils, and vegetation. In fact, the most
stereotypically "urban" characteristics of cities are also those which can cause tem-
peratures to rise. By replacing vegetation and soil with concrete and asphalt, we reduce
the landscape's ability to lower daytime temperatures through evapotranspiration,
and lose the obvious benefits of shade. And by using dark-colored materials on roads,
buildings, and other surfaces, we create entire cities that absorb, rather than reflect,
incoming solar energy.
The combination of reduced reflectivity—called "albedo"—and reduced vegetation
has resulted in a temperature difference between urban and rural areas that is most
clear in late afternoon and early evening, when roads, sidewalks, and walls begin to
release the heat they have stored throughout the day. The difference is most extreme
in densely developed areas. In fact, heat islands are broken up partially by parks and
other vegetated areas, even within the downtown area (See Figure ES-1).
Meteorologists and other scientists have been aware of this phenomenon for over
100 years. But throughout the last century, increasing rates of urbanization and in-
dustrialization have exacerbated the heat island effect. Peak temperatures in Los An-
geles, for instance, have risen by 5°F in the last fifty years. Peak temperatures in other
cities of northern California and Texas, as well as Washington, D.C., Shanghai, and
Mexico City, have also risen throughout the century. Figure ES-2 shows a historical
comparison of rural and urban temperatures in California.
Higher urban
temperatures
increase the
demand for
electricity.
What Are The Effects Of Increased Urban Temperatures?
Increased Electricity Demand
A winter heat island in a cold climate can be a moderate asset because it lowers
heating bills. In warm and hot climates, however, the higher temperatures result in increased
energy demands for air conditioning. Initial research shows that for every 1°F increase
in summer temperatures, peak cooling loads will increase 1.5 to 2 percent. Since urban
temperatures during summer afternoons in the United States have increased by 2 to 4°F
XVIII
image:
Executive Summary
in the last four decades, we can assume that
3 to 8 percent of the current urban elec-
tricity demand is used to compensate for
the heat island effect alone.
These percentages may seem nominal,
but they cost a great deal. The 5°F in-
crease in Los Angeles' peak temperatures
since 1940, for instance, is estimated to
have added electricity demands of 1.5 gi-
gawatts (approximately one and a half
new, large power plants)—with an esti-
mated hourly cost of $150,000. Similarly,
the cost of Washington, D.C.'s heat island
has been estimated at $40,000 per hour.
A rough estimate of the national electric-
ity costs for the added urban heat is
around $1 million per hour, or over $1
billion per year.
Increased Smog Production
Summer heat islands also increase
smog production; the incidence of smog
events may increase by 10 percent for each
5°F increase in temperature. In Los Ange-
les, for example, ozone levels are not likely
to exceed the National Ambient Air
Quality Standard (NAAQS)—currently 12
parts per hundred million (pphm)—when
temperatures are below 74°F. Above that
threshold, however, peak ozone levels
exceed health standards more often (See
Figure ES-3). Ozone levels frequently
reach unacceptable levels at or above 94°F.
Similar threshold phenomenon have been
found in other areas as well.
Increased Emission of Carbon Dioxide And
Other Pollutants
Increased air conditioning increases
electricity generation at power plants. Plants
that run on fossil fuels typically emit many
pollutants, including sulfur dioxide, carbon
monoxide, nitrous oxides, and suspended
particulates. Perhaps more importantly,
burning fossil fuels or wood produces large
amounts of carbon dioxide, which many
Temperature Trend in 31 California Urban and Rural Stations
-i.o
1900
1920
1940 1960
Year
1980
2000
Source Akbari et al . 1990, based on data from Goodnch, 1989
Figure ES-2.
Urban areas are getting warmer Since 1940, the temperature difference be-
tween urban and rural stations has shown an increase of 0.67° F per decade (Also
appears as Figure 1-15.)
Smog
•*« i
sured as Ozone
Per 100 Million)
: £ S S K £ 8 S &
S z "
Z | 12
O)
I J 101
C/J a. _
4-
2:
Smog
Incre
i
NAAQS (12 pphm)
•
Levels in Los Angeles
Hazard . *
ases
i • •
•• • •••• •••• •
-
50 60 70 80 90 100
Daily Maximum Temperature (°F)
Source Akbari et al , 1990
Figure ES-3.
Rising temperatures and smog: This graph shows ozone concentrations com-
pared to daily peak temperatures in Los Angeles, California As temperatures rise
above 74°F, ozone concentrations can more frequently exceed the
National Ambient Air Quality Standard (NAAQS) which is currently 12 parts per
hundred million (Also appears as Figure 1-23)
XIX
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure ES-4.
Sample residential land-
scape A large tree is
planted on the east side
to shade the air condi-
tioner, and on the west
and south sides to cast
maximum shadows on
the house Shrubs
planted on a/I sides of
the house help to reduce
the temperatures of soil
and walls (Also appears
as Figure 6-9)
Air
Conditioner
Source Parker, 1982
scientists believe could contribute to changes in climate (IPCC, 1991). If so, urban heat
islands could be contributing to this problem, since increased air conditioning leads to
increased power generation and carbon dioxide emissions.
Tree Planting And Light-Colored Surfacing To Reduce Urban Temperatures
Trees affect climates and building-energy use in two ways. Direct benefits accrue
from the shade that trees provide to buildings and surfaces. By blocking solar radiation,
trees prevent structures and surfaces from heating up beyond the ambient air temperature.
Indirectly, trees cool buildings by cooling the air surrounding them through evapotrans-
piration. In a process similar to sweating, trees use heat to evaporate water from a leaf
before it can heat the air, thus cooling the air immediately around the leaf. The cumulative
effect of many leaves and many trees can cool the air in a large area.
Direct Effects
Tree shade does a better job cooling a building and its interior than Venetian blinds,
plastic coatings, or reflective patinas on glass. Field measurements have shown that
through shading, trees and shrubs strategically planted next to buildings can reduce
summer air-conditioning costs typically by 15 to 35 percent, and by as much as 50
image:
Executive Summary
percent or more in certain specific situ-
ations. Simply shading the air condi-
tioner—by using shrubs or a vine-covered
trellis—can save up to 10 percent in
annual cooling-energy costs.
Placement of trees is very important.
Proper placement can ensure that trees
shade the areas most critical in lowering
internal temperatures, and shade them at
the most critical times of the day. For
example, trees should be placed to shade
the east, west and south sides of a building
in order to block late morning, afternoon,
and early evening sun (See Figure ES-4).
In addition, trees which shade windows
provide the most benefit. However, im-
properly positioned trees can increase the
cost of energy.
During the winter, shade (especially
from the south) can be a liability, as it
blocks the warming rays of the sun, which
can otherwise reduce heating energy re-
quirements. Broadleaved or deciduous trees
drop their foliage in the fall and allow most
of the sunlight to come through the bare
limbs. Proper pruning of larger trees allows
the low-angled winter sun to come in under
the lowest branches.
Evergreen or coniferous trees and
shrubs can be positioned to reduce the in-
fluence of cold, winter winds on the heating
requirements (See Figure ES-5). It is very
important that these windbreaks not impede
winter sunlight. Houses measured in South
Dakota, for example, consumed 25 percent
less fuel when located on the leeward sides
of windbreaks than when exposed. Wind-
breaks on three sides—north, west, east—
reduced fuel consumption by 40 percent.
This guidebook discusses proper placement
of trees and vegetation in detail. Figure ES-
6 shows estimated direct savings in heating
and cooling energy from a 30 percent
increase in tree cover around older houses.
Coniferous
windbreaks protect
house from cold
winter winds.
Trees close
to house on
east and west protect
against summer sun
Trees on south side should
be deciduous to permit
winter sun while shielding
the summer sun.
TIT
Summer
Winds
Avoid dense trees in the
direction of summer
winds that block
desired cooling breezes
Source Huang, 1990
Figure ES-5.
Strategic planting example. In temperate climates, trees must be chosen and
planted to shield a house from both the hot summer sun and the cold winter
winds (Also appears as Figure 6-101
200
ISO
Changes in Expenditures for Energy:
Wind-Shielding and Shading Effects
f
1 100
50
lit
| i T
gcS I
j Heating
I Cooling
Source Huang et al , 1990
Figure ES-6.
Wind-shielding and shading effects The net direct effects of a 30 percent
increase in tree cover on the heating and cooling energy use of older houses, based
on computer simulations (Also appears as Figure 2-6.)
XXI
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Sacramento Lake
Charles
(LAI
* Percentages refer to savings of
total cooling energy use
Source Huang et al , 1990
Figure ES-7.
Estimated cooling savings in a typical well-insulated new house from the
combined direct and indirect effects of trees Note that direct effects provide a
relatively small percentage of the total energy savings for new housing stock
(Also appears as Figure 2-9)
Indirect Effects
The evapotranspirative properties of
trees can produce even greater indirect ef-
fects on temperature and energy consump-
tion. Figure ES-7 shows a comparison of
the relative savings attributable to indirect
and direct effects of trees. As the number
of trees increase, the relative contribution
of the indirect effect grows in comparison
to the direct effects. Trees transpire up to
100 gallons of water in a day. In a hot dry
climate, this cooling effect equals that of
five air conditioners running for 20 hours.
When the effects of evapotranspiration are
combined with the effect of strategically
placed shade, temperatures can drop by as
much as 9°F in the immediate vicinity of
the trees. Increasing vegetation cover by
just 10 and 30 percent (about one and
three properly placed trees per house, re-
spectively) may reduce cooling energy by as much as 10 to 50 percent, depending
on housing stock type, age, construction and other factors. (Typically, older and more
poorly insulated buildings, and those in hotter, drier regions, will have larger energy
savings.) These numbers apply only to shade trees carefully placed to maximize their
shading effects.
City-wide programs to plant street trees and to fill our parks, corporate lawns,
and plazas would enhance the shading and evapotranspirative benefits of urban trees.
Such an increase in the urban canopy would improve our communities in other ways,
too. For instance, trees filter air pollutants, mask noise, and prevent erosion. They
provide habitat for wildlife and birds, and may inspire feelings of relaxation and hap-
piness in humans. Massive tree-planting programs can revitalize our dying urban forests,
while sponsoring community cooperation and civic pride.
Finally, urban trees can contribute to slowing or preventing potential changes in
climate. Urban trees not only sequester carbon dioxide from the atmosphere, but they
also help prevent carbon dioxide emissions in the first place by reducing the need for
air conditioning. Researchers estimate that the energy conserving properties of community
trees may increase their contribution to reducing carbon dioxide levels by a factor of
five to ten compared to trees planted at a distance from buildings. If enough trees are
planted, we may be able to reduce our cooling energy enough to avoid both the costly
construction of new power plants as well as their economic and environmental costs.
Light-Colored Surfaces
Our built environments contain myriad surfaces, including building roofs and walls,
streets, freeways, parking lots, driveways, school yards, and playgrounds. When these sur-
faces are dark, they absorb heat. When they are light, they reflect heat and stay cooler.
XXII
image:
Executive Summary
The measure of a surface's reflectivity
is called albedo. Humans in tropical and
sub-tropical communities (Greece and
North Africa for example) have been white-
washing their walls and streets to keep
albedos high—or very reflective—and tem-
peratures low for centuries. In this country
and other countries, people may have for-
gotten the practical cooling effect that such
light colors can have. Dark-colored houses
and streets create hotter communities and
increased use of air conditioning.
Many studies exist which show that
increasing surface albedos lower surface
temperatures (See Figure ES-8). To date,
few field measurements exist that doc-
ument reductions in energy use from
changing dark-colored surfaces to light
ones in houses and communities. Com-
puter simulations of a typical house in
Sacramento, California, indicate that its
total air-conditioning bill could be re-
duced by up to 22 percent if the albedo
of the roofs and walls are increased from
0.2 to 0.6 (See Figure ES-9). Such in-
creases entail no drastic measures, and
simply changing grey siding to off-white,
and replacing dark-colored roof shingles
with light-colored ones, would signifi-
cantly increase the house's overall albedo.
Like trees and vegetation, reductions
in temperatures and energy use from albedo
modifications accrue to both individual
buildings and entire neighborhoods. In fact,
the indirect effects of albedo modification
may be larger than the direct ones. Com-
puter simulations of neighborhoods show
that changing roof, wall, and street colors
could significantly reduce air temperatures
and cooling energy use. Researchers esti-
mate that realistic albedo changes could re-
duce a city's air temperature by as much
as 5°F in hot, sunny climates with many
dark surfaces. This, in turn, would produce
indirect energy savings as high as 40 per-
Effects of Surface Color on Temperature
0 12 0 U 0 12 0 12 0 12 0 12 0 12
60
Source Griggs el al , 1989
Figure ES-8.
Effects of Surface Color on Temperature Actual measurements of roof tempera-
tures showed that dark-colored surfaces become increasingly hotter throughout
the day compared to light-colored surfaces (Also appears as Figure 3-4.)
Direct Cooling Energy Savings from Increased Albedo
Savings
(S/year)
250
Minneapolis Pittsburgh Chicago Washington Sacramento Miami Phoenix
j OLD HOUSES
1 NEW HOUSES NOTE: Percentages indicate savings of total energy cost
Source Taha, 1988
Figure ES-9.
Cooling Energy Savings from Direct Effects of Increased Albedo Significant
energy savings from increasing the surface albedo in selected cities across the
country as projected by computer models Note higher dollar savings in sunbelt
cities (Also appears as Figure 3-6.)
XXIII
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Filling 100
million urban
tree spaces and
lightening sur-
face colors on a
large scale could
reduce U.S.
energy use by 2
percent and cut
carbon emissions
by 1 percent,
annually.
cent. When the direct and indirect savings of albedo changes are combined, the total
energy savings simulated by a computer approached 50 percent during average hours
and 30 percent during peak cooling periods.
In addition to these significant savings in energy, albedo modifications are likely
to be inexpensive. Because changes can be incorporated into normal maintenance
cycles (i.e., repainting walls, replacing roof shingles, or repaving asphalt surfaces),
they add little or no extra costs to building owners or city governments.
Trees And Light-Colored Surfaces
Clearly, both trees and light-colored surfaces can have a significant effect on
the temperatures and energy consumption of our homes, offices, and communities.
Taken together, however, the effect of these two measures is even more striking. Some
scientists estimate that if 100 million urban tree spaces in this country were filled
(that's three trees for one-half of the single-family homes in this country) and if light-
colored surfacing programs were implemented, we could reduce our electricity use
by as much as 50 billion kilowatt hours per year (2 percent of annual electricity use
in the United States). In addition, the amount of CO2 released into the atmosphere
could be cut by as much as 35 million tons per year (about 10 million tons of carbon)
roughly 1 percent of annual U.S. CO2 emissions.
Do These Strategies Cause Problems?
Neither planting trees nor changing surface colors are faultless measures. In-
creasing trees may increase the amount of water needed for irrigation and the amount
of solid waste generated in a community. Preliminary analysis suggests, however,
that using trees to replace lawns can drastically reduce water needs in a commu-
nity, and that using shrubs or groundcover to replace trees can reduce water usage
even further. In arid climates, using native vegetation that is less dependent on high
volumes of water also reduces water needs.
The problem of disposal (potentially large amounts of leaves, twigs, branches,
and other debris from vegetation deposited in landfills) also does not loom as large
on closer inspection. Leaves can be used for compost, while branches and fallen
trunks can be used for firewood, large-scale composts, or boiler fuel. Clearly, any
community embarking on a large-scale tree-planting program could also consider
the merits of community-wide composting and yard debris programs. Depending on
the region and other factors, the combined benefits of urban tree planting will often
be greater than the costs incurred, especially when planting directly around houses
(See Figure ES-10).
Questions regarding albedo primarily focus on glare and soiling. That is, a
community containing many light-colored surfaces may be uncomfortable to the
eye. This does not seem to be a problem; cities in the Tropics and Middle East
have had predominantly white surfaces for centuries. By contrast, some critics
have claimed that white surfaces will soil too quickly to be effective. Studies show,
however, that even soiled, light-colored surfaces can have a higher albedo than
dark-colored ones.
XXIV
image:
Executive Summary
Costs and Benefits of Community Trees
• Park Benefits
D Park Costs
Yard Benefits
Yard Costs
Street Benefits
Street Costs
15
1993 1998 2003
2008 2013
Year
2018 2023 2028
Source McPherson, 1991
Developing Programs To Plant Trees And Change Surface Colors
One way to begin programs for tree planting and light-colored surfacing strategies
is through public education. That is, providing information on the albedo of building
materials, the shade potential of trees, and energy-savings of direct and indirect
measures will inspire consumers to implement some measures. Developing ordinances
will also spur energy-conserving measures.
Many communities in this country already have tree-planting programs and or-
dinances in effect. The simple addition of landscaping and albedo modification
suggestions could enhance the overall benefits of existing programs.
Because no urban community in the United States or abroad has yet initiated a
formal program of albedo modification, we have no experience with successful
implementation practices, potential drawbacks, and conflicts with other urban issues.
We would like to stress, however, that our preliminary analysis indicates that the
energy and environmental benefits of albedo modifications are high, while the costs
and potential risks can be strikingly low.
Conclusions And Recommendations
Research on the effects of urban heat islands is coming at a time of great public
concern about local and global environmental conditions. Air pollution, water pollution,
and the possibility of global climate change all mandate that we decrease our energy
use. In addition, America's urban forests are in a state of decline. Half of the potential
Figure ES-10.
Projected annual costs
and benefits of the Trees
for Tucson/Global ReLeaf
reforestation program
This graph shows the rela-
tive benefits of the loca-
tion of planting Benefits
are plotted in the back
row, and costs in the front
row Note the high ben-
efits associated with
planting trees around
houses (yard) (Also ap-
pears as Figure 2-13)
XXV
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure ES-11.
This figure illustrates
strategic tree-planting
and light-colored surfac-
ing activities that could
yield energy-conserving
results for homeowners.
spaces for trees along streets are unfilled, and only one quarter of urban trees that
die each year are replaced.
At the same time, our city sizes are growing at unprecedented rates. By the year
2000, fifty percent of the world's population will live in cities, where only 14 percent
lived 100 years ago. Correlating population size to heat-island intensity is still inexact.
It is clear, though, that heat islands intensify as urban areas grow. Already, urban
temperatures in this country can be 8°F hotter than those in surrounding areas, and
urban temperatures in tropical and sub-tropical countries are as much as 15°F higher
than their surroundings.
Specifically, the following tasks could be undertaken to reduce urban temperatures
and the attendant levels of energy use and smog production:
1) Undertake or expand community-wide programs for shade tree planting and add al-
bedo modification. These programs can consist of volunteer programs in conjunction
with community tree planting and development groups, and public education.
2) Promote energy conserving activities by providing information on albedo of building
products, suggestions for landscaping designs, and the energy savings possible—through
retailers of building materials and trees, through forestry extension agents, city for-
esters, contractors, and through utilities and municipalities.
3) Provide incentives for developers to build well-arbored, light-colored, energy efficient
buildings and communities.
XXVI
image:
Executive Summary
4) Encourage Public Utility Commissions to provide utilities with incentives to support
tree planting and surface color enhancements.
5) Utilities can support these activities as a way to reduce demand for peak power and
perhaps reduce the need to build new power facilities.
6) Corporations can encourage energy conservation by sponsoring tree planting and light-
colored surfacing programs among their employees and in the communities in which
they and their employees reside.
7) Professional groups can create professional education materials so that their mem-
berships are conversant with new techniques for community planning, tree planting,
and other modifications to traditional practices.
8) Municipalities can pass tree ordinances, specify the use of light-colored paving ma-
terials in road building and renovations, provide financial incentives, or zone for light-
colored building materials in commercial areas, strengthen the ability of roads and
parks departments to plant new trees and maintain existing ones, and foster community
efforts in these areas.
9) Professional schools and other educational programs could incorporate these principles
in the training of builders, engineers, architects, city and urban planners and designers,
arborculturists, foresters, and landscape architects.
Today, inspired by President Bush's "America the Beautiful" tree-planting program,
and by efforts like the American Forestry Association's Global ReLeaf Network, and those
of many successful city tree-planting organizations, citizens across the Unites States are
planting trees in their communities. By combining those programs with these landscap-
ing and albedo modification suggestions, we can create communities that are cooler, more
aesthetically pleasing, and more energy efficient.
XXVII
image:
Introduction
The Urban Landscape
Construction Of The Urban Habitat
Over the past two million years, humans have drastically modified their envi-
ronment. With fire, they cleared large areas of forest and grass lands. With
plant and animal cultivation, they created entirely new landscapes—by genetically
"engineering" native plants, transporting species to new areas, and re-directing water
for irrigation. When humans started building urban centers, they began the most
radical transformation possible—the replacement of vegetated landscapes with con-
structed cityscapes.
During the past century, this environmental transformation accelerated at an
unprecedented pace. Industrialized society—with its emphasis on manufacturing,
transportation, and urbanization—has affected many areas on the planet. Indeed,
the impacts of industrialization on the landscapes and atmosphere are so significant
that some people say no place on earth is free of human influence.
Much of this influence is not readily evident. Pollutant gases and contaminated
soils are not always discernible. The ozone hole is not visible in the southern sky.
The ocean hides the products of our disposable society in deep basins.
The most visible places of human influence are the cities. Rolling hills and
pastureland have been leveled and paved over with asphalt roads and concrete side-
walks. Productive fields have been replaced with parking lots. Buildings are constructed
where trees once naturally grew and thrived. Smog and noise often fill the air.
In creating these urban areas, humans inadvertently have also created their own
microclimates with heightened air temperatures, unique windflow patterns, noise,
and pollution. The material in this book, Cooling Our Communities: A Guidebook
on Tree Planting and Light-Colored Surfacing, is specifically concerned with
increased temperatures of the urban environment, the problems caused by this increase,
and the potential methods for modulating the temperatures of our homes and
communities while reducing electricity demand and costs.
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
The "intensity" of the heat island—that is, just how much hotter a city is than its
countryside—may seem slight. The effect of the heat islands is usually a temperature
rise of 2 to 8 degrees Fahrenheit (°F). Multiplied across the country, however, these
higher urban temperatures may be costing us billions of dollars each year in energy
expenditures, smog damage, and increased water consumption. Analysis of data from
electric utilities indicates that for each degree Fahrenheit increase in temperature, peak
power demand rises by one to two percent. Besides costing rate payers more than one
million dollars an hour during hot periods, increased power generation raises levels
of atmospheric carbon dioxide—a major contributor to the greenhouse effect. Research
also indicates that these increased temperatures exacerbate levels of smog in cities.
It is clear that urban heat islands have major effects on energy costs and the quality
of urban life. It is also clear that effective ways of mitigating heat islands exist, and
that, fortunately, these methods are fairly simple and inexpensive to implement.
Opportunities For Cool Communities
Urban areas accumulate greater amounts of heat for several reasons. Many of
these factors—including climate, topography, and weather patterns—cannot be changed.
Two heat island factors we can influence are the amount of vegetation and the color
of surfaces. These two factors are responsible for the majority of additional heating
attributable to human activities.
Vegetation cools cities by directly shading individual buildings, and by evapo-
transpiration. Evapotranspiration is the process by which a plant releases water vapor
into the air. Entire neighborhoods and cities can be cooled by evapotranspiration.
Unfortunately, in the last several decades, more and more trees were removed from
urban environments. As vegetation disappeared, temperatures began to rise. Today,
only one tree is planted in our cities for every four removed.
The color of a city's surfaces determines the amount of solar energy absorbed
or reflected. Dark building materials—roofing tiles, shingles, tar, asphalt, and gravel—
absorb more sunlight than light-colored surfaces. In this country, most buildings and
roads are dark. Each time we build them, we continue to drive up the temperature
of our cities.
Two of the most cost-effective methods of reducing heat islands are strategic
landscaping and light-colored surfacing. Strategic landscaping refers to planting trees
and shrubs around buildings and throughout cities to provide maximum shade and
wind benefits. Light-colored surfacing means changing dark-colored surfaces to ones
which more effectively reflect—rather than absorb—solar energy.
The combined effects of planting more trees and incorporating more light-colored
surfaces can be astonishing. Preliminary research indicates that late afternoon air
temperatures on a hot summer day can be reduced by 5 to 10°F, resulting in cooling
energy savings of up to 50 percent, depending on location. Implementing these mea-
sures may be cheaper than implementing other efficiency programs.
In addition to mitigating environmental concerns, planting trees and changing
surface colors provide many other physical, functional, and psychological benefits
image:
Introduction: The Urban Landscape
to urban dwellers. Trees help reduce noise and particulate matter in the air, and
provide habitat for wildlife. Both trees and light-colored surfaces enhance the aesthetics
of urban spaces, thereby contributing to the psychological well-being of their in-
habitants.
The Guidebook
This volume is an initial attempt to address this problem. It compiles existing
information on the causes, effects, and most viable mitigation strategies of urban
heat islands. As such, it necessarily has some strengths and some weaknesses.
The primary strength of this volume is that it collects the most current research
on heat islands in the country. A number of researchers, in particular the Heat Island
Project of the Energy Analysis Program at Lawrence Berkeley Laboratory, have been
studying the problem of heat islands for several years. This book documents and
reflects their efforts. In addition, this is the first book to suggest the ways in which
homeowners and policymakers can take steps to reduce heat islands.
The concepts of strategic landscaping and light-colored surfaces are not difficult
to understand, but implementing community-wide programs requires considerable
planning and constant maintenance.
The first chapter of the guidebook introduces the causes of heat islands and their
effects on urban areas. The second and third discuss planting trees and changing surface
colors to reduce those heat island effects. The remaining chapters discuss implemen-
tation of programs for heat island mitigation, and describe several programs already
in operation.
The authors developed the guidebook for the benefit of lay readers. Citizens,
policymakers, and urban planners are provided with a general view of the scientific
research that is underway to understand and mitigate the effects of urban heat islands.
In the back of the book, the authors have included technical appendices to assist
analysts seeking more detailed information.
Definitions
There are several technical terms that appear throughout the guidebook and are
defined here for the reader's convenience.
Albedo. The ability of a surface to reflect incoming electromagnetic radiation
measured from 0 to 1. A surface with an albedo of 1 reflects all incoming
radiation, while one with an albedo of 0 absorbs all of it.
Building cooling load. The hourly amount of heat that must be removed from a
building to maintain indoor comfort is known as the building's "cooling
load." This measurement, generally used by architects and engineers, is
given in British Thermal Units (Btus).
Caliper. The standard measure for the diameter of a tree measured six inches above
the ground (for trees larger than one half inch and smaller than four inches
in diameter).
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Cooling electricity use. The amount of electricity used to meet the building cooling
load is referred to as its "cooling electricity use."
Gigawatt. A gigawatt is a unit of energy equal to a billion watts or a million kilowatts.
Kilowatt (kW). A kilowatt is a unit of electric power equal to 1000 watts, which
is the work represented by an electric current of one ampere under the pressure
of one volt.
Kilowatt-hour (kWh). A kilowatt-hour is a unit of energy equal to that expended
by one kilowatt of electricity in one hour.
Megawatt (mW). A megawatt is a unit of energy equal to 1000 kilowatts.
Microclimate. The localized climate conditions within an urban area or neighborhood.
National Ambient Air Quality Standard (NAAQS). The NAAQS is a mea-
surement of ozone concentration, currently equivalent to 12 parts-per-
hundred-million. Smog levels that exceed this measurement are considered
problematic.
Peak building cooling load (or peak load). The maximum hourly amount of heat
that must be removed from a building to maintain required indoor comfort
conditions is known as "peak building cooling-load." In this book, this term
often appears in a shortened form as the "peak load."
Peak cooling electricity use. The maximum amount of electricity needed to meet
the cooling load of a building is referred to as its "peak cooling elec-
tricity use."
Peak electricity demand. The maximum electricity used to meet the cooling load
of a building or buildings in a given area is known as "peak electricity de-
mand." Peak electricity demand is measured in kilowatts.
Quad. One quadrillion Btus (British Thermal Units), approximately equivalent
to the yearly production of 17 large nuclear power plants (1000 megawatts
each).
Utility load. The total electricity demand for a utility district is referred to as the
"utility load" of that district.
image:
1
The Urban Heat Island:
Causes and Impacts
What Is An Urban Heat Island?
One of the most telling characteristics of a city is its temperature. Visit any city
on a hot summer day and you will feel waves of blistering heat emanating from
roads and dark buildings. Travel from the city to the countryside after sunset, and
you will notice that the settled areas are still hot and muggy, while the rural areas
are rapidly cooling.
Even within a city, different neighborhoods have different temperatures, depending
on the surroundings. Parks are the coolest, for example. Neighborhoods with many
trees are cooler than those with few. Downtown areas full of concrete and tall buildings
are the hottest of all. These differences may seem obvious, but they also illuminate
an often-ignored fact: human activities affect the climate within which we live. More
specifically, in creating urban landscapes, humans have made them significantly hot-
ter—usually between 2 and 8°F hotter—than their surrounding rural areas.
Hashem Akbari
Susan Davis
Joe Huang
Philip Liu
Haider Taha
The "Urban
Heat Island" is a
moderate asset
during the
winter, raising
city tempera-
tures and low-
ering heating
bills. During the
summer, how-
ever, heat is-
lands intensify
"heat waves,"
increasing
electricity use
for air condi-
tioning, adding
to human dis-
comfort, and
exacerbating
urban smog.
Figure 1-1.
Comfort in the shade and
moist air Temperatures
can noticeably vary even
within a city, depending
on the amount of sur-
rounding vegetation and
surface colors
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Data from
electric utilities
indicate that for
each degree
increase in
temperature,
power use rises
by 1-2 percent
because of the
increased need
for air condition-
ing. Nationwide,
this increased
demand could
cost ratepayers
more than a
million dollars
per hour or
possibly over
one billion
dollars per year.
Figure 1-2.
Rural building (andair con-
ditioner) shaded by trees:
Shading urban homes
with strategically placed
vegetation can help to re-
gain both the quality of
environment and cooling
advantages of the rural
landscape
Meteorologists who first noticed this phenomenon more than a century ago,
labelled it the "urban heat island." These heat islands influence most of the major
cities around the world. In the United States, for instance, the temperature of New
York City can be 10°F hotter than its outlying areas. Inner-city St. Louis is 2 to 8°F
hotter than its surroundings. Perhaps the most striking effect of heat islands is found
in tropical cities that receive a great deal of sunshine. Records indicate that the heat
island effect in New Delhi, India, can be 10°F, while in Mexico City, Mexico, it can
raise urban temperatures by an additional 18°F.
image:
The Urban Heat Island: Causes and Impacts
What Causes Urban Heat Islands?
While the nature and effects of urban heat islands are still being studied, the causes
are well established. Denuded landscapes, impermeable surfaces, massive buildings,
heat-generating cars and machines, and pollutants all help to make urban areas hotter.
The replacement of vegetation or soil by concrete or asphalt reduces an urban
landscape's ability to lower daytime temperatures through evaporation and plant tran-
spiration. In a rural or irrigated landscape, a large amount of daytime solar energy
is actually spent on evaporating water, not on raising air temperatures. Trees and
other vegetation perform this function through the process of "evapotranspiration."
In this process, the plant draws moisture from the ground, utilizes what it needs for
growth and moderating its own temperature, transpires the excess, and cools the
surrounding air.
When a natural vegetative cover is replaced by asphalt or concrete, it loses its
ability to moderate temperatures. Instead, the solar energy normally delegated to the
evaporation process is left to raise surface temperatures.
Urban areas get hotter than rural settings not only because their ability to cool
evaporatively is reduced, but also because they reflect less incoming solar energy.
This reflective capacity is called "albedo."1 Asphalt, in particular, has low albedo;
it absorbs almost all the solar energy falling on it. This, combined with asphalt's in-
ability to evaporate water, means that streets and parking lots paved with this material
often reach blistering temperatures on sunny summer afternoons.
Buildings also contribute to the urban heat island in a number of ways. Like pave-
ment and sidewalks, buildings do not have the capacity to moderate heat through
evaporation. Instead, they absorb and store the day's heat, and then radiate it back
to the urban atmosphere at night. You can feel this heat if you stand close to a brick
building early on a summer evening.
In downtown areas, the densely clustered, tall office buildings create "urban can-
yons" that take hours to cool off every night. In addition, buildings and other archi-
tectural structures obstruct the natural flow of breezes, making wind speeds noticeably
lower in the cities. This obstruction prevents winds from carrying heat build-up away
from the city and from assisting in the reduction of the heat island.
Urban pollution also affects the heat island, depending on the time of day and
season of the year. During daylight hours, pollution lowers heat build-up slightly,
because it blocks incoming solar energy. At night, however, pollution prevents heat
from escaping by covering the city like a blanket, and thereby increasing the heat
island effect. Finally, heat and pollution from cars, machines, and other mechanical
systems contribute to winter heat islands. During the summer, however, solar energy
is so intense that it overwhelms the heat output from these human activities. Con-
sequently, the severity of the summer heat island is determined largely by the interplay
of the urban landscape and solar radiation.
Urban areas get
hotter than
rural settings
not only be-
cause their
ability to cool
evaporatively is
reduced, but
also because
they reflect less
incoming solar
energy. This
reflective ca-
pacity is called
•"albedo."
1 Albedo differs from "reflectivity" in that it is measured across all wavelengths, rather than just the
visible spectrum. Since more than half of the solar radiation is invisible to the eye, albedo is a more
precise term when discussing the ability of surfaces to reflect solar radiation.
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 1-3.
Urban canyons block
breezes Urban canyons
are typically found in the
downtown area of large
cities. There, tall and
densely clustered build-
ings obstruct the flow of
natural breezes that could
carry heat build-up away
from the city at night.
image:
The Urban Heat Island: Causes and Impacts
What Is The Temperature Pattern In A Typical Urban Heat Island?
With the exception of slight variations due to geographical or climatological fea-
tures, the overall pattern of heat islands is remarkably consistent from city to city.
Starting from the countryside, temperatures rise distinctly at the edge of the city.
Temperatures continue to rise slowly closer to downtown, with pockets of cooler
air hovering over parks or other wooded areas. The highest temperatures, or "peaks,"
in the urban heat island are almost always in the downtown areas. The center of the
city usually contains the highest density of buildings, and there seems to be a direct
correlation between the amount of buildings per unit area and variations in tempera-
tures. Figure 1-4 illustrates the heat island effect for a hypothetical metropolitan
area. Figures 1-5 and 1-6 show recorded heat island effects in two cities.
Variations in the urban heat island over time are also consistent from city to city.
The thermal processes causing summer heat islands occur when the sun is shining.
The difference in temperatures begins to grow in mid-morning. The heat island, how-
ever, is most pronounced two to three hours after sunset, when paved areas and build-
ings slowly release their stored heat into the urban atmosphere. Figure 1-7 shows
how the recorded heat island contours in St. Louis changed over the course of a day.
Sketch of an Urban Heat-Island Profile
92°-
\ ,'*"""•:
Suburban Commercial
Residential
Suburban
Residential
Rural
Farmland
Source Andrasko and Huang, 1990
How Much Hotter Is An Urban Heat Island ?
Although most cities today suffer from heat island effects, their intensities—
that is, just how much hotter the cities are than their surrounding areas—depend on
a number of factors. Climate, topography, and physical layout certainly influence
a city's average temperature. Short-term weather conditions also have a strong effect.
Breezes in a city, for instance, prevent the formation of heat islands by mixing cooler
air from surrounding areas with warmer urban air. On windless, cloudless days, stag-
nant urban air hovers over cities and holds heat that is released from city surfaces.
In the last century, increasing urbanization and industrialization have exacerbated
the heat island. As cities have grown, increasing numbers of buildings have crowded
out trees and other vegetation. It is estimated that, at present, only one tree is planted
Figure 1-4.
Sketch of a typical urban
heat-island profile: This
profile of a heat island in a
hypothetical metropolitan
area shows temperature
changes (in degrees Fahr-
enheit) correlated to the
density of development
and trees.
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 1-5.
Winter heat island in London: This
map shows temperature variations
in downtown and surrounding Lon-
don, England. Even in winter the
contrast of high temperatures in
the inner city and lower tempera-
tures in surrounding rural areas
is observable. Here, the differ-
ence is 12°F
Figure 1-6.
Neighborhood temperatures in Mon-
treal: This map shows temperature
variations (degrees Fahrenheit) in
LaFontame Park and surrounding ar-
eas of Montreal, Canada. Notice that
the temperatures are lower over the
park, due to the cooling effects of
trees.
Source Landsberg, 1981
Built-Up
D
Open
and Park
0 200
meters
(0-600 feet)
Source Oke, 1977
10
image:
The Urban Heat Island: Causes and Impacts
6a.m.
3p.m.
10 a.m.
9p.m.
Source Vukovich, et al , 1979
Downtown St. Louis D Built-up Area
0246
Miles
Figure 1-7.
Heat island profile in downtown St. Louis, Missouri. Although heat islands differ in their intensity and their size, most exhibit a
similar pattern throughout the day. Notice that at 10:00 a.m., the temperature difference between downtown areas and
surrounding areas is apparent, but it is only about 3°F. This is because although the sun has been shining for several hours, the
dark surfaces have not yet absorbed enough heat to make the temperatures rise At 3:00 p m., the temperature difference is
still slight—in this instance, only 2°F By 9:00 p m., however, after the sun has set, there is a marked 7°F difference between
downtown and the area surrounding the city, because the pavements and other dark areas are releasing the heat stored there
throughout the day That difference continues throughout the evening and into the early morning hours. Indeed, the 6:00 a.m.
frame shows a significant, lingering heat island of 6°F for this city.
11
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Population can
be seen as one
indicator of a
heat island's
intensity. This
can be particu-
larly trouble-
some for cities
in the tropical
areas of the
world, where
populations are
expected to
skyrocket in the
for every four removed in American
cities. For example, New York City
has lost 175,000 trees, or 20 percent
of its urban forest, in the past ten years.
This loss of vegetation and its replace-
ment by buildings or pavement causes
the urban heat island to intensify.
Population also can be seen as
one indicator of a heat island's inten-
sity. Several studies of different cit-
ies in North America and Europe
have shown that cities with larger
populations tend to have more in-
tense heat islands (See Figure 1-8).
This does not bode well for the
future. Already, the number of urban
City Size and Heat Island Intensity
\t"
J! •
Is:
• NORTH AMERICAN CITIES
EUROPEAN CITIES
100,000
Population
1,000,000 10,000,000
Source Oke, 1987
Figure 1-8.
Maximum difference in urban and rural temperatures Re-
searchers have found correlations between city size and
city temperature
dwellers has risen from 600 million in 1900 to 2 billion in 1986. If this growth con-
tinues, more than one-half of the world's population will live in cities by the end
of this century, where 100 years ago, only 14 percent lived in cities. In the United
States, 90 percent of the population is expected to be living in, or around, urban areas
by the year 2000 (Brown, 1987).
The situation will be even more dramatic in developing countries. Already, twenty-
one of the thirty-four cities with more than 5 million inhabitants are in developing
countries. Current projections estimate that eleven of those cities will have populations
of between 20 and 30 million by the year 2000. In other words, our cities may be
hot now, but they are going to get even hotter (Brown, 1987).
What Do Historical Records Show About Urban Temperature Trends?
Complete historical records of urban temperatures are not available at this time for
a number of reasons. First, not all cities have maintained temperature records. Second,
available records are usually only a century old, and contain so many changes in weather
station location and instrumentation that comparisons are extremely difficult. Third, most
temperature data taken in the last forty years have come from airport, rather than urban,
weather stations. These data may underestimate urban temperature trends, because airports
are usually located in the outskirts of cities, where temperatures are generally cooler.
Fourth, data on summer temperatures have not always been compiled for all cities.
Despite these data limitations, climatologists and researchers can still see that
cities across the planet are getting progressively hotter than their surrounding areas.
Since the turn of the century, average annual temperatures in many cities have increased
by as much as 5°F. The next section discusses first historical trends in absolute urban
temperatures in several cities in California, selected cities elsewhere in the United
States, and several cities abroad. It then focuses more closely on the relative differences
between urban and rural temperatures, or the urban heat island. In the absence of
summer data, we used average annual and maximum annual temperatures.
12
image:
The Urban Heat Island: Causes and Impacts
Absolute Urban Temperatures
The historical data for several Californian cities with mild to warm climates show
an obvious warming trend. Figure 1-9 shows that the maximum yearly temperatures
in Los Angeles dropped 0.5°F per decade from the late 19th century until 1930. Summer
temperatures began rising, and have continued to rise at a steady rate of 1.3°F per
decade. Today, maximum temperatures in downtown Los Angeles are about 5°F higher
than in 1940. Average yearly temperatures in Los Angeles since the 1940s have risen
by about 0.8°F per decade.
The cooling trend in the first third of the century probably was a result of irrigation
and agricultural development on what had been sparsely vegetated ground. The pro-
fusion of fields and orchards had the inadvertent, but beneficial, effect of cooling
the city. After the 1930s, however, as the urban population began to expand, agricultural
areas were replaced by buildings and dark roads. As these surfaces heated and cooling
effects of vegetation were lost, city temperatures began to rise.
Other cities in California are also warming. San Francisco's average August
temperatures are increasing at a rate of 0.2°F per decade, as shown in Figure 1-
10. This rate is lower than that in Los Angeles, but still significant, especially if
we remember that San Francisco is well ventilated and open to the ocean. Other
cities in California, including Oakland, Sacramento, and San Diego, are also warming
at significant rates. Figures for these cities are located in Appendix A at the back
of this guidebook.
Maximum Daily Temperatures
Los Angeles, California — Downtown
106 °F
99 °F
1880 1900 1920 1940 1960 1980 2000
Annual
San Francisco, California
0.2 °F/decade
66
£"
£
62
58
56
1850
1900 1950
Annual
2000
Source Akbari, et al , 1990
Source Taha, 1991
Figure 1-9. Figure 1-10.
Los Angeles (CA) temperature record: Meteo- San Francisco (CA) temperature record. Even
rological records show that yearly maximum though this c/ty is located on a peninsula, average
temperatures have been rising 1 3° F per decade since August temperatures for San Francisco show a
1940. Today, peakdowntown temperatures are about 0.2°'F rise in temperature per decade
5°F higher than they were 50 years ago
13
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Warming trends are also evident in other parts of the country. Figure 1-11 shows
annual mean temperatures for Washington, D.C. from 1871 to 1987. Since 1900, the annual
mean temperatures have risen by a steady 0.5°F per decade, resulting in a total increase
of about 4°F over 80 years. The actual increase is probably higher than indicated in this
figure, since the weather station was moved from downtown to cooler airport locations
in 1942 (indicated by the vertical line in Figure 1-11). Similarly, Ft. Lauderdale's (FL)
summers have been warming at about 0.2°F per decade, as shown in Figure 1-12.
Data from foreign countries indicate similar, if less drastic, temperature increases.
Figure 1-13 shows that the annual mean temperatures in Shanghai (China) have increased
by 1.2°F over the last 100 years. Figure 1-14 shows that the annual mean temperatures
in Tokyo, Japan, have increased by 3°F between 1915 and 1965. Table 1-1 summarizes
the observed temperature trends for cities mentioned in this section and in Appendix A.
Differences Between Urban And Rural Temperatures
Because of the scarcity of data directly comparing urban and rural temperatures,
it is often difficult to ascertain how much of the urban warming trend resulted from
changes in regional weather, and how much is the result of the urban heat island effect.
But the available data indicate that urban temperatures are rising faster than tem-
peratures of surrounding rural areas.
In California, comparisons of 31 urban and rural weather stations show that urban
sites were all relatively cooler before 1940, as illustrated in Figure 1-15, because
cities were the centers of irrigation. After 1940, however, urban temperatures became
Washington, D.C.
O.SjF/oecade
52
1900
2000
Fort Lauderdale
O.ISjF/decade
1900
1920
1940 1960
Annual
1980
2000
Source Taha, 1991
Source Taha, 1991
Figure 1-11. Figure 1-12.
Washington, D C temperatures Since 1900, annual Fort Lauderdale (FL) temperatures: Average August
mean temperatures in Washington, D.C. have risen temperatures for Fort Lauderdale show a 0.2° F rise in
by a steady O.ff'F per decade temperature per decade The increase is lower in this
city because it is oceanside
14
image:
The Urban Heat Island: Causes and Impacts
62
Shanghai
0.12jF/decade
58
1860 1880 1900 1920 1940 1960 1980
5-yrs period ending
Tokyo
0.6°F/decade
59
58
57
56
55
1910 1920 1930 1940 1950 1960 1970
Annual
Source Taha, 1991
Source Taha, 1991
Figure 1-13. Figure 1-14.
Shanghai (China) temperatures: Annual mean tern- Tokyo (Japan) temperatures' In Tokyo, the annual
peratures in Shanghai have increased by T.2°F since mean temperatures increased by 6"F between 1915
1860. See also Figure 1-16 which shows a record of and 1965
the "temperature difference" between urban and
rural areas of Shanghai during 1960 and 1980.
Table 1-1. Measured temperature trends in selected cities
City
Los Angeles
Los Angeles
San Francisco
Oakland
San Jose
San Diego
Sacramento
Washington
Baltimore
Ft. Lauderdale
Shanghai
Shanghai
Tokyo
Trend
(" F/decade)
1.3
0.8
0.2
0.4
0.3
0.8
0.4
0.5
0.4
0.2
0.12
0.2
0.6
Type of Recording
highs
means
means
means
means
means
means
means
means
means
means
minima
means
Sources: For identification of individual sources see description under Further Reading.
15
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Temperature Trend in 31 California Urban and Rural Stations
1.5-,
-1.0
1900
2000
Source Akbari et al . 1990. based on data from Goodrich, 1989
Figure 1-15.
California heat islands. Since 1940, the temperature difference between urban
and rural stations has shown an increase of 0 67°F per decade.
Shanghai Urban and Rural Temperatures
1.4
in
09
09
1 1-0 H
CO
I 0.8
01
01
0.6
0.4
0.2
0.2 ° F/decade
1960
1970
Year
1980
Source Taha, 1991
Figure 1-16.
Shanghai heat island: Since 1960, the temperature difference between urban
and rural Shanghai has increased by 0 2°F per decade
as high, if not higher, than those in the
suburbs. After 1965, this trend became
quite obvious; temperatures rose at about
0.7°F per decade.
Similarly, the difference between an-
nual mean urban and rural temperatures
in Shanghai grew from 0.4°F in 1962 to
1°F in 1980 (See Figure 1-16). Under
ideal conditions (clear and calm nights,
for example), a heat island of 10°F has
been measured in that city.
Tropical cities provide excellent ex-
amples of increasing heat island intensity.
Indeed, it is not unusual for average tem-
peratures in tropical and subtropical cities
to be as much as 10 to 18°F higher than
surrounding areas. Heat islands of 16°F
have been measured in Mexico City
(Mexico), and of 11°F in Bombay and
Poona (India).
Urban Heat Islands And Energy Use
Heat islands can have either beneficial
or detrimental impacts on energy use, de-
pending on geography, climate, and other
factors. In a cold climate, an urban heat
island is a moderate asset because it raises
wintertime temperatures and lowers heating
bills. In warm to hot climates, however, it
exacerbates cooling energy use in the sum-
mer. For U.S. cities with populations larger
than 100,000, peak utility loads will in-
crease 1.5 to 2 percent for every 1°F in-
crease in temperature. Since urban tempera-
tures during summer afternoons in the
United States have increased by 2 to 4°F
in the last four decades, it can be assumed
that 3 to 8 percent of the current urban elec-
tricity demand is used to compensate for
the heat island effect alone.
The negative effects of urban heat
islands should be a concern for all cities
with significant cooling seasons. Figure 1-
17 shows the United States separated into
four general climate zones: Cold, Temper-
16
image:
The Urban Heat Island: Causes and Impacts
ate, Hot-Arid, and Hot-Humid. Cities in the first zone typically have cold long winters
and mild short summers. The effect of urban heat islands in these locations is generally
positive, with some improvement of winter conditions and small increases in energy
use during the short summer. Current thinking suggests that lightening surfaces and
planting trees, however, will probably have little effect on winter heat islands. Hence,
mitigation strategies for summer heat islands would still be a benefit in these areas.
Cities in the second zone have moderately cold winters, and mild to hot summers
varying in length from three to four months. The effect of urban heat islands in these
locations are generally detrimental, since their winter benefits do not compensate
for their significant degradation of summertime conditions and increased air-con-
ditioning demand. Cities in the last two zones have short mild winters and long hot
summers. There, the urban heat island definitely intensifies temperatures and increases
demand for air conditioning.
Correlations between temperature and energy use can be established by comparing
utility-wide electricity loads to temperatures at the same time of day. Selecting the
same hour each day is necessary to minimize non-climate related effects on electricity
demand, such as those from utility-imposed schedules. Most utility districts experience
peak electricity demands around 4:00 p.m. in the summer. (When hourly temperature
data are not available, we correlate daily temperature averages with peak loads. This
difference in method seems to have little effect on the results.)
Comparisons of temperatures to utility loads for the Los Angeles area have con-
sistently shown that the two are interrelated. There are two electric utilities serving
Figure 1-17.
Climate regions based on
heating and cooling re-
quirements.
Source Based on degree-day data from the National Climate Data Center, 1991
17
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
the metropolitan area, the Los Angeles Department of Water and Power (LADWP)
and Southern California Edison (SCE). The 1986 data for LADWP showed that the
peak demand increased by 72-75 megawatts (MW) or 2 percent for each 1°F increase
in temperature (See Figure 1-18). Similarly, the data for the larger SCE district showed
peak demand increases of 225 MW, or about 1.6 percent, for each 1°F increase in
temperature (See Figure 1-19).
If we combine the data for the two districts, the net rate of increase in Los Angeles
is 300 MW/°F. Therefore, the 5°F increase in Los Angeles' peak temperatures since
1940 translates into an added electricity demand of 1.5 gigawatts due to the heat island
effect. Since peak electricity is worth approximately 10 cents per kilowatt-hour (kWh),
this added burden costs the Los Angeles basin $150,000 per hour.
In Washington, the increase in electricity demand is reported to be 100 MW or
2 percent for each 1°F increase in temperature. This means that the 4°F increase over
the past 80 years has contributed 400 MW to the utility load, at a cost of $40,000
per hour. Since there are approximately 1300 hours of air conditioning in Washington,
the increase in yearly energy costs approaches $50 million. Table 1-2 and Figure 1-
20 present data from various utility districts showing similar relationships between
demand and temperature.
These rates of increase may not seem very high. But their impact on the national
energy bill is impressive. The total electricity consumption for residential and com-
mercial air conditioning in the United States is estimated at about 260 billion kilowatt
hours per year, worth over $20 billion. Our initial calculations indicate that the elec-
tricity costs for summer heat islands alone could be as much as $1 million per hour,
or over $1 billion per year. Hence, the nation-wide response of peak-cooling electricity
load to temperature in the United States could range from 0.5 to 3 percent for each
1°F rise in temperature. Figures 1-21 and 1-22 show the results from a computer study
of the potential energy impacts of rising temperatures in the southern part of the United
Megawatts
2,000'
ill
•
1
1
I Maximum
Load
Mean Load
Minimum
Load
55 60 65 70 75 80 85 90 95
Temperature °F
14,000-
B 12,000-
O5
s 10,000-
8,000-
-'Hill
i
1
I Maximum
Load
Mean Load
Minimum
Load
45 50 55 60 65 70 75 80 85 90 95 100
Temperature °F
Los Angeles (CA>- LADWP
Source Taha, 1991
Los Angeles (CA): SCE
Source Taha, 1991
Figure 1-18 and Figure 1-19.
Electricity Load. These plots show 400pm. electricity loads—maximum, mean and minimum loads—for two utility districts correlated
with air temperatures: Los Angeles Department of Water and Power (Figure 1-18) and Southern California Edison (Figure 1-19) Note that
as air temperatures rise, electricity loads a/so increase, due to increased demand for air conditioning.
18
image:
The Urban Heat Island: Causes and Impacts
Table 1-2. Correlation between temperatures and electricity demand for
selected utility districts based on measured data for 1986.
Utility District
Los Angeles (LADWP)
Los Angeles (SCE)
Washington, D.C.
Salt River Project (Phoenix)
Dallas-Ft. Worth (TX)
Tucson (AZ)
Colorado Springs (CO)
Increase
(MW/°F)
75
225
100
56
250
12
4
Increase
(% /°F)
2.0
1.6
2.0
2.0
1.7
1.0
1.0
Source Taha, 1991
Figure 1-20. Electricity records for four cities These plots also show the correlation of air temperatures with electricity load in the cities
of Dallas (upper left), Colorado Springs (upper right), Phoenix (lower left), and Tucson (lower right). Again, notice that as temperatures rise,
so does the increase in electricity demand from increased air-conditioning use
14,000
g 12,000
s
(a
o>
i 10,000
8,000
'III!
lltll
ii
1 Maximum
Load
Mean Load
Minimum
Load
25 30 35 40 45 50 55 60 65 70 75 80 85
Temperature °F
500
450
400
I 350
300-
250
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
Temperature°F
Da/las (TX)
Colorado Springs (CO)
h Mean Load
Minimum
3000-1 .
2,500-
1 low-
s'
1,500-
1,000-
:,;|ii(|,|
I1'1
45 50 55 60 65 70 75 80 85 90 95 100 105 110 115
Temperature °F
1 Maximum
Load
Mean Load
Minimum
Load
1200
1100
1000-
i»
5
800
700
600'
E
I
i g i i
"Hlliij
I''
•
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Temperature °F
1 Maximum
Load
Mean Load
Minimum
Load
Phoenix (AZ)
Tucson (AZ)
Source Taha, 1991
19
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 1-21.
Estimated temperature
increases in the United
States: Estimated in-
creases in average and
peak temperatures in
various regions in the
United States due to glo-
bal climate change, un-
der the assumptions of
one study
Figure 1-22.
Estimated electricity in-
creases in the United
States- Estimated in-
crease in peak and an-
nual electricity use in
various regions of the
United States with in-
creases in regional tem-
peratures
Source Linder and Inghs, 19
Peak Demand
Annual Energy Use
Source Linder and Inglis, 1989
20
image:
The Urban Heat Island: Causes and Impacts
States. Figure 1-21 shows the estimated
changes in average temperatures due to
global climate change, although results
are speculative until climate change mod-
els provide better regional resolution. Fig-
ure 1-22 shows the estimated impacts of
these temperature changes on electricity
use in the same regions.
The increasing demand for electricity
will continue if our cities continue to warm,
either from heat islands or global warming.
Such warming can affect a utility in two
ways. First, it can increase the amount of
new generating capacity that a utility has
to build and maintain to meet increased
cooling demand. Second, logistical prob-
lems arising from the reallocation of re-
sources, in terms of scheduling, importing,
and exporting, could cost utilities across
the country millions of dollars.
Urban Heat Islands and Smog Levels
In addition to increasing cooling en-
ergy use, heat islands and long-term urban
warming affect the concentration and
distribution of urban pollution, because
heat accelerates the chemical reactions
in the atmosphere that lead to high ozone
concentrations.
Polluted days may increase by 10
percent for each 5°F increase. In Los An-
geles, for example, ozone levels are not
likely to exceed the current National Am-
bient Air Quality Standard (NAAQS)1
when temperatures are below 74°F.
Above that threshold, however, peak
ozone levels increase. At 94°F and above
they reach unacceptable levels (Figure 1-
23). A similar threshold phenomenon
was found in 13 cities in Texas (Figure
1-24). There, high urban temperatures
sured as Ozone
Per 100 Million)
: s s s K K s a *
S a "]
1 1 *
o e in
* „:
J;
Smog Levels in Los Angeles
Smog
Incre
i
NAAQS (12 pphm)
Hazard . '
ases
L • •
-
-
50 60 70 80 90 100
Daily Maximum Temperature (°F)
Source Akban et al , 1990
Smog Levels in Texas
40
36^
32^
E
•§. 28-
I 24^
S
I 20
1 16-
>. 1
•= i?
s ™
Smog Hazard
Increases
i
NAAQS (12 pphm)
...•_.
* *
—
"«".!."
. " . I. *.-*. I." • .
-
. ." : ::.::.. j::::::::::::::^::::."
I.:::::::::::::::::::::::::::::::::::::::::::::::-.
":"::::::r:::~:::" :::"":•••: ~T: :•:••-.:::
20 40 60 80 100 120
Daily maximum temperature (°F)
Source Argento. 1988
Figures 1-23 and 1-24.
Ozone concentrations compared to daily peak temperatures in downtown Los
Angeles in 1985 (Figure 1-23), and ozone concentrations compared too daily peak
temperatures in 13 cities in Texas (Figure 1-24). Note that as temperatures rise,
ozone concentrations reach dangerous levels (levels above the current National
Ambient Air Quality Standard—NAASQ—of 12 parts per hundred million)
'The current National Ambient Air Quality Standard (NAAQS) is an ozone concentration of 12 parts per hundred million
(pphm). Ozone concentrations that exceed this measurement are considered problematic.
21
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
associated with the heat island effect also increase the probabilities of exceeding
the NAAQS.
The relationship between air temperature and air pollution levels, however, is
not simple. Other characteristics of city air, including dew point (the temperature
at which air becomes saturated and begins producing dew), air pressure, cloud cover,
and wind speed, also affect pollution levels. Emissions and concentrations of acidic
gases and particles also are greater in urban areas. And the deposition of acidity in
urban areas may be increased locally by enhanced rain volume due to heat-island-
generated differences in air circulation.
To add to the complexity of these interactions, urban geometry also plays an
important role in the transport and removal of pollutants. On the one hand, the
roughness of urban buildings and landscapes increases air turbulence, thereby en-
hancing the dispersion of pollutants. On the other hand, if pollutants land in sheltered
areas—like street canyons—they may reside longer than they would in a breezy
rural environment.
Heat island effects on urban winds also influence the concentration and dispersal
of pollutants. When incoming winds are fairly slow, winds within cities actually
increase, due to heat-island-generated differences in temperatures. Conversely, when
incoming winds move more quickly (a condition when heat islands cannot develop
as fully), winds within the city slow down, due to the roughness of the buildings and
urban structures.
Heat islands also affect urban pollution in less direct, but equally important, ways.
Increased air-conditioning results in an increase in power generation, which produces
larger amounts of pollutants. Average daily emissions from a representative (500
megawatt electric) coal-fired power plant consist typically of about 28 tons of sulfur
dioxide (SO2), two tons of carbon monoxide (CO), 28 tons of nitrous oxides (NO2),
and 1.4 tons of suspended particulates. These latter two are the major constituents
of urban smog.
Urban Heat Islands And The Greenhouse Effect
The data just described show that temperatures in cities, especially large ones,
have been increasing for at least the last four decades. There is no evidence that this
warming trend will stop, or even slow. Indeed, based on results that scientists have
obtained from computerized climate models, this trend may even accelerate because
of the greenhouse effect.
The greenhouse effect occurs when the atmospheric concentration of greenhouse
gases (carbon dioxide, methane, and nitrous oxides, among others) forms a blanket
over the earth's surface. This blanket reduces heat loss through re-radiation from
the planet's surface, which leads to increased global temperatures.
A natural greenhouse effect has existed for millions of years. Without it, the earth
would be 50 to 60°F colder than it is. Human activities, however, particularly the
burning of fossil fuels, are now changing the concentration of greenhouse gases radi-
cally. (This may cause the earth to warm at a rate that could far exceed any other
22
image:
The Urban Heat Island: Causes and Impacts
experienced on earth.) Researchers and analysts are working to understand the potential
impacts of global climate change in an effort to learn possible methods for adapting
to and slowing changes, such as reducing the emissions of greenhouse gases.
Scientists from organizations all over the world are forecasting that if current
trends continue, we could see an increase in the mean global temperature of 2 to 5°C
(3.6 to 9°F) by the end of the next century (IPCC, 1991). This could alter ocean and
atmospheric currents, shift precipitation patterns, raise sea levels, and lower the levels
of inland waterways. There could be reductions in the range of existing forests, the
loss of significant portions of the U.S. coastal wetlands, and regional adjustments
in agriculture due to a northward shift in productive regions. Finally, the higher tem-
peratures could require increases in the production of electric power to meet additional
air-conditioning needs. This generation could cause increases in the concentrations
of ozone in the troposphere, that part of the atmosphere within 8 to 10 kilometers
of Earth's surface (Morgenstern, 1991). In short, changes in climate have the potential
to alter social, economic, agricultural, political, and ecological systems.
Important greenhouse gases include carbon dioxide (CO2), methane (CH4), chlo-
rofluorocarbons (CFCs), nitrous oxide (N2O), and tropospheric ozone. Among these
gases CO2 is considered the primary factor affecting global warming. This gas is
a by-product of both fossil fuel combustion and deforestation. On a global scale,
world energy use represents the largest anthropogenic source of CO2; it exceeds the
amount released from deforestation by two to five times. Taken together, the burning
of fossil fuels combined with deforestation has quadrupled global rates of anthro-
pogenic CO2 emissions over the past 150 years. Atmospheric concentrations of CO2,
for example, have risen from about 315 parts per million to about 350 parts per million
Figure 1-25.
The Greenhouse Effect'
Greenhouse gases in the
entire atmosphere warm
the earth just as glass
traps warm air in a real
greenhouse
23
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 1-26.
Electricity use and car-
bon dioxide (CCy emis-
sions: Turning on the air
conditioner at home in-
creases C02 emissions
at the power plant
where they are released
into the atmosphere.
this century, up sharply from estimates of approximately 290 parts per million in
the 1800s (Lashof and Tirpak, 1991). The U.S. Department of Energy estimates that
the CO2 emissions in the United States could increase by 380 million tons of carbon
by the year 2010, and by 900 million tons of carbon by the year 2030, 66 percent
above current emission levels (IPCC, 1990). If emissions remained constant at 1985
levels, the atmospheric concentration of CO2 might reach 440-500 parts per million
by 2100 (Lashof and Tirpak, 1991).
Heat islands also may contribute to global warming. Scientists do not know what
the direct impact of urban temperature increases may be on global temperatures. As
the temperature of urban areas rises, they demand increased energy for cooling, which
requires additional power generation. Each kilowatt hour of electricity generated,
in turn, releases about one half pound carbon—in the form of carbon dioxide—into
the atmosphere. (The average city of 100,000 people uses approximately one billion
kilowatt hours per year.) An unchecked cycle of increasing temperatures leading to
increased electricity demand followed by increased power generation, atmospheric
emissions, and higher temperatures, might begin. This means that if energy demand
can be reduced by alleviating heat islands, the amount of CO2 released into the at-
mosphere also can be reduced.
Whatever global climate change does occur would amplify an increase in urban
temperatures, if current trends continue. Preliminary work by a number of researchers
indicates that if the current trends of heat islands continue, cities would be 10°F hotter
24
image:
The Urban Heat Island: Causes and Impacts
in 50 years. As mentioned earlier, Figure 1-21 shows the results obtained by one
research group of estimated increases in temperatures for various regions of the United
States. This heating would result in greater discomfort, higher ozone levels, more
electricity use, and more carbon dioxide emissions. An effective program of heat-
island mitigation could help curb this dramatic urban warming.
If urban temperatures are not lowered in the near future, both energy and smog
generation will continue to increase, as will the costs associated with that generation.
This increase may occur whether global warming happens or not, and it could result
in some social and economic consequences.
The America the Beautiful
Urban and Community Forestry Assistance Program
In 1990, Congress passed President Bush's America the Beautiful
Act as part of the 1990 Farm Bill. The President's goal for the program
is to plant one billion trees per year. The Community Forestry element
of the America the Beautiful program calls for a nationwide, multi-year
effort to plant and maintain trees in all 40,000 cities, towns, and com-
munities throughout the country. The goal of the program is to plant 30
million trees, the largest community tree planting and maintenance pro-
gram in history. It seeks to reverse the current trend of deforestation in
the Nation's cities and towns, where on average only one tree is planted
for every four that die or are removed.
The Act gives leadership to the U.S. Forest Service in the Department
of Agriculture and creates a non-profit foundation called the National Tree
Trust. The Forest Service, working with state forestry agencies and other
partners, is providing technical advice and support to communities and
volunteer groups in their tree planting and tree care endeavors. The Na-
tional Tree Trust Foundation is bringing the public, private, and civic sectors
together, soliciting funds to assist communities, and encouraging volunteer
community tree-planting programs. Funds raised by the Foundation can
be used to assist communities in preparing sites, and selecting, planting,
and maintaining trees.
To get involved with the America the Beautiful Urban and Community
Forestry Assistance Program, or for more information, contact your state
forester, or write to the National Tree Trust, 1455 Pennsylvania Avenue
NW, Suite 250, Washington, D.C., 20005.
—Source: USDA Forest Service, 1991
25
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
y^
Further Reading
Several books by climatologists describe urban climate and the heat island effect,
including The Urban Climate by H. Landsberg (1981), and Boundary Layer Climates
by Oke (1978). The technical papers by Oke (1975, 1987), and Duckworth and
Sandberg (1954) describe measurements of heat island intensities. The paper by Myrup
(1969) describes a simple computer analysis of the urban heat island. The proceedings
from the Urban Climatology Workshop in Mexico City (Oke, 1986) has numerous
articles by Oke, Landsberg, and others on urban heat islands in tropical cities.
The proceedings from the Heat Island Workshop by LBL (Garbesi, ed. 1989)
contain numerous articles on various aspects of the urban heat-island issue, including
computer analyses of urban climates, estimated costs of heat islands, and the energy
saving potentials of and implementation methods for mitigation strategies. In ad-
dition, there are several LBL reports by Akbari and others on the energy costs and
potential mitigation strategies of urban heat islands.
The papers by Hartig, Hull and Harvey, Schroeder, Ulrich, and Verderber describe
the psychological effects of trees on humans.
Urban temperatures and heat island discussions in this chapter were based on data
from Goodridge (1987, 1989) and Karl et al. (1987, 1988, 1990). The historical
temperature data from California urban and rural weather stations were obtained from
Goodridge (1987, 1989) and further discussed in a paper by Akbari et al. (1989). The
weather data for Washington, B.C. were obtained from the Potomac Electric Power
Company whereas the temperature data for Baltimore and Ft. Lauderdale were obtained
from Karl et al. (1990). The urban temperature data for Shanghai and Tokyo are based
on studies by Chow (in Oke 1986, pp. 87-109) and Fukui (1970). The heat island data
for Mexico City, Bombay, and Poona are taken from Oguntoyinbo (in Oke 1986, pp.
110-135) and Jauregui (1973). The computer-based estimates of future changes in
annual and peak temperatures for various parts of the United States are taken from
a report by Linder and Inglis (1989).
Utility load data for the two Los Angeles area utilities were obtained from the
Los Angeles Department of Water and Power and the Southern California Edison
Company. The utility load data for Salt River Project, Dallas-Ft. Worth, Tucson, and
Colorado Springs were obtained from their respective utilities. The estimated
temperature sensitivity of peak demand and energy use for various parts of the country
are again taken from the Linder and Inglis report (1989).
Comparisons of smog levels to temperature in Los Angeles are based on data from
the California Air Resources Board. Comparisons of ozone levels to temperature in
Texas cities are based on data from Argento (1988). Estimated amounts of power plant
emissions are taken from a Department of Energy report (1988). General data on the
relationship between heat islands and urban pollution can also be found in Feng (1990),
Summers (1966), and NAPAP reports (1990). Information on heat islands and wind
speeds can be found in Balling and Cerveny (1987), Bornstein et al. (1977), and Lee
(1979). Finally, analyses of urban air quality modeling are available in Bennett and
Saab (1982), Freeman et al. (1986), and Ivanyi et al. (1982).
26
image:
The Benefits of Urban Trees
Joe Huang
Ronald Ritschard
Neil Sampson
Haider Taha
Vegetation is one of the simplest and most effective ways to cool our commu-
nities and save energy. Trees, shrubs, and vines can protect individual buildings
from the sun's heat in the summer, and from frigid winds in the winter. On hot, sunny
days, evapotranspiration from trees and shrubs also can reduce temperatures and
energy use for whole neighborhoods, even entire cities. Indeed, this collective cooling
can have a greater influence on energy use than shading and wind shielding.
LEAVES, TWIGS
BRANCHES:
absorb sound and
block erosion-
causing rainfall.
EVAPOTRANSPIRA TION:
from leaves cools
surrounding air.
ROOTS, LEAVES
TRUNKS:
provide habitat
for birds,
animals, and
insects.
BRANCHES,
LEAVES: provide
shade and reduce
wind speed.
LEAVES: filter
dangerous
pollutants from
the air.
ROOTS:
stabilize soil
prevent
Figure 2-1.
The numerous ecological
qualities of trees: Indeed,
almost every pan of a tree
provides a beneficial func-
tion. The leaves alone can
provide cooling from
evapotranspiration, shel-
ter from wind, sound ab-
sorption, and sequester-
ing of carbon dioxide
27
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Vegetation has other benefits as well. It is cheap, fairly simple, and aesthetically
pleasing (nobody raves about the appearance of insulation or air conditioners). It can
increase property value, block noise, and stabilize soil. These benefits increase as
trees get older and bigger.
The effectiveness of vegetation, of course, depends on its density, shape, dimen-
sions, and placement. But in general, any tree, even one bereft of leaves, can have
a noticeable impact on energy use.
Direct Effects Of Vegetation
Trees affect urban climates and building energy use in two ways. Shading and
lowering wind speeds modifies the interaction between a building and its surroundings.
These are called "direct" effects. "Indirect" effects, like evapotranspiration, are those
that change the surrounding urban environmental conditions. In general, direct effects—
like shade—accrue to one building while the benefits of indirect effects accrue to
a whole neighborhood or city.
During the winter, shading is not desirable in temperate and cold climates, because
it will increase heating needs. Blocking the wind, however, is a benefit in the winter.
During the summer, the opposite is true: shading helps reduce energy needs, while
wind screening can reduce cooling breezes. With strategic planting, we can maximize
the positive effects in both seasons, while minimizing the negative ones.
Shading
Trees in full leaf can be very effective in blocking the sun's radiation. While the
full extent of a canopy's shade depends on the species, vegetation of the right shape
and density can block up to 95 percent of the incoming radiation. Even leafless trees
(such as deciduous trees in winter) can intercept up to 50 percent of the sun's energy.
Tree shade reduces cooling energy use inside a building in three ways. First, shad-
ing windows helps prevent direct solar radiation from entering the structure. Second,
shading walls, windows, and roofs keeps them from getting hot, thereby reducing
the amount of heat reaching the interior. Third, shade similarly keeps the soil around
a building cool, which can then act as a "heat sink" for the house.
The shade of trees actually does a better job cooling a building and its interior
than Venetian blinds, plastic coatings, or heavy, reflective coatings on glass. Figure
2-2 illustrates the dynamic relationship between deciduous shade trees and incoming
solar radiation.
Several studies have shown that trees can increase property values by 3 per-
cent to 20 percent. The American Forestry Association in 1985 estimated that the
future value of an urban tree is $57,000 for a 50 year-old mature specimen. This
estimate includes an average annual value of $73 for air conditioning, $75 for soil
benefits and erosion control, $50 for air pollution control, and $75 for wildlife habi-
tats. The total value over the tree's lifetime would be the total annual value of
$273 (1985 dollars), compounded at 5 percent interest for 50 years.
— Neil Sampson
28
image:
The Benefits of Urban Trees
SUMMER
WINTER
Source Heisler, 1986
Shade And Energy Use
Field measurements have found that the shade of trees and shrubs planted immediately
adjacent to buildings can directly reduce cooling needs. Dr. John Parker, a researcher
at Florida International University, estimated that trees and shrubs planted next to a
South Florida residential building can reduce summer air-conditioning costs by 40 percent
(Parker, 1983). Reductions in summer power demand of 3 kilowatts (59 percent) during
mornings and 5 kilowatts (58 percent) in afternoons were also measured. Parker noted
that the most effective position for trees is close to windows and glazed areas. He also
indicated that directly shading the air conditioner can increase its efficiency by up to
10 percent during the warmest periods. Measurements taken in Central Pennsylvania
suggest that shading a small mobile home can reduce air conditioning by up to 75 percent
(Heisler, 1986). See Chapter 6 for more exact steps on landscaping for energy conservation.
Tree shading is beneficial during the summer, but not in the winter, when the
warming rays of the sun are desirable. The penalties from tree shading in winter,
however, are not as significant as the benefits are during the summer. Tne sun is less
intense in winter, and deciduous trees shed their leaves which allows most of the
sunshine to reach the house.
Figure 2-2.
Shading characteristics of
deciduous trees during
the summer and winter.
29
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Changes in Expenditures for Energy:
Shading Effect
Source Huang et al , 1990
Figure 2-3.
The effects of shading from a 30 percent increase in tree cover on the heating and
cooling energy use of older houses, based on computer simulation.
100
3? 80
60
09 40
5 20
Wind Speed Reductions in Residential
Neighborhoods Compared to an Open Field
0
0 20 40 60 80 100
Percent Area Covered by Trees and Buildings
Source Heisler. 1989
Figure 2-4.
Tree cover and wind speed reduction: Measured studies show that an added 10
percent tree cover can reduce urban wind speeds by 10-20 percent Even in
winter, wind-speed reductions are as much as 50-90 percent of the summer
reductions.
Figure 2-3 shows the results of com-
puter simulations of the impact of addi-
tional tree shading on the heating and cool-
ing energy use of typical houses in seven
cities. Although tree shading increased
winter heating bills, these increases are
more than offset by the much larger sav-
ings in cooling energy use.
Even the heating penalties shown in
Figure 2-3 must be interpreted with care,
since they relate only to the effects of tree
shading. In reality, trees also reduce wind
speeds, which is a benefit during the win-
ter, as described in the following section.
Consequently, the net impact of added
trees on building energy use is beneficial,
even in the winter.
Wind Reduction
Trees also reduce wind speeds. Indeed,
the area within a single crown or stand of
trees can be very calm, even when the wind
is strong outside the stand. Houses in
neighborhoods also help keep wind speeds
down. Increasing the number of trees, how-
ever, can help get wind speeds down even
further. This is a benefit in the winter, but
a detriment in the summer when cooling
breezes are welcomed.
How much foliage does it take to reduce
wind speeds? Dr. Gordon Heisler, of the U.S.
Forest Service, has found that even scattered
trees can significantly decrease the wind
speed in residential neighborhoods. Figure
2-4 shows the results from Heisler's study
of wind speeds in various neighborhoods.
Depending on the density of housing, an
added 10 percent tree cover in a residential
area can reduce wind speeds by 10 percent
to 20 percent, while an added 30 percent tree
cover can reduce it by 15 percent to 35
percent. The study also showed that even
in wintertime, when most trees are leafless,
wind speeds can be reduced by as much as
50-90 percent of their summer values.
30
image:
The Benefits of Urban Trees
In the winter, such wind reductions help
keep a building warmer. In the summer,
blocking the wind sometimes has the unde-
sirable effect of blocking cooling breezes,
too. It is possible, however, to plant trees
around buildings to channel winds and
create cooling ventilation. (Chapter 6, pre-
sents additional information on strategic
planting to channel wind.)
Wind and Energy Use
Wind-speed reductions resulting from
tree planting can either decrease or increase
both cooling and heating energy use, de-
pending on local weather conditions. In
Figure 2-5, for example, we can see that
wind-speed reductions simulated in com-
puter models lowered both heating and
cooling energy use in Chicago, IL, Miami,
FL, and Washington, D.C. In Phoenix, AZ,
Pittsburgh, PA, Sacramento, CA, and Min-
neapolis, MN, however, the heating energy
use was reduced but the cooling energy con-
sumption was increased.
Field measurements have also indicated
that reduced wind speeds can be beneficial
to heating-energy users. Houses monitored
in South Dakota, for example, consumed 25
percent less fuel when located on leeward
sides of windbreaks than when exposed.
With wind breaks on three sides of houses,
fuel consumption was reduced by an aver-
age of 40 percent. Between January and
February, exposed houses used 442 kilo-
watt-hours per month to keep the tempera-
ture at 60°F, but only 270 kilowatt-hours
per month when sheltered by vegetation.
Net Energy Impacts of Trees
Since the direct effects of planting
trees around a house include both shading
and wind shielding, it is important to
evaluate the net impact of these two effects
on a building's heating and cooling energy
bill. In Figure 2-6, we have simulated both
Changes in Expenditures for Energy:
Wind-Shielding Effect
150
WO
-50
| Heating
I Cooling
I
-
1
Source Huang et al , 1990
Figure 2-5.
The effects of wind shielding from a 30 percent increase in tree cover on the
heating and cooling energy use of older houses, based on computer simulation.
200
150
Changes in Expenditures for Energy:
Wind-Shielding and Shading Effects
50
| Heating
I Cooling
I
Source Huang et al , 1990
Figure 2-6.
The net direct effects of windshie/ding and shading from a 30 percent increase
in tree cover on the heating and coo/ing energy use of older houses, based on
computer simulation
31
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
the wind-shielding and shading effects from planting three trees around a typical
house built before 1973. The estimated energy savings shown in the figure combine
those estimated for the individual effects shown earlier in Figures 2-3 and 2-5. When
the wind-shielding and shading effects are considered together, trees are shown to
reduce both the heating and cooling energy use in both hot and cold locations. During
the winter, trees reduce heating costs through their wind-shielding effects, while
during the summer, trees reduce cooling costs through their shading effects. In fact,
the computer study shows annual energy cost savings from three additional trees to
be $75 to $175 per household in all seven cities.
Indirect Effects of Vegetation
Evapotranspiration, the process by which plants release moisture in the form
of water vapor, requires energy from solar radiation or warm air. When solar energy
is expended for evapotranspiration instead of directly heating the air, the increase
in temperatures during the day will be reduced.
This process can have a significant effect on air temperatures. Trees can transpire
up to 100 gallons of water a day. In a hot, dry location, this produces a cooling effect
similar to that of five average air conditioners running for 20 hours. In a hot, humid
location, however, evapotranspiration is not an effective cooling process.
Evapotranspiration and shading effects together can reduce air temperatures by
as much as 9°F, LBL researchers have found. Even cropped surfaces can be 5°F cooler
than their denuded surroundings. Temperature measurements by LBL in suburban Davis
and Sacramento, CA, indicate that the air temperature in neighborhoods with mature
tree canopies are 3 to 6°F lower in the daytime than newer areas with no trees.
Even more pronounced cooling effects have been measured in large urban parks,
where evapotranspiration is increased by wind. In such parks—referred to as oases—
temperatures can be up to 7°F lower than surrounding neighborhoods. The cooling
influence of these oases extends far beyond the immediate foliated area. In experiments
in Davis, for example, LBL researchers found that temperatures of the air leaving
an orchard remained low for a distance five times the height of the trees.
The indirect effects trees have on reducing air temperatures through evapotrans-
piration are much more difficult to predict using computers than are the direct effects
of shading and wind-shielding. Preliminary results produced by researchers, however,
The American Forestry Association's Global ReLeaf Utility Program is suc-
cessfully convincing utility, companies to plant trees for energy conservation.
The Utility Program invites companies to sponsor Global ReLeaf as part of
a customer education/community and public relations program. Individual cus-
tomers learn how to plant trees to save energy and money. Communities are
encouraged to develop tree-planting projects—and to support them. The program
also gives utility employees background on the savings potentials of trees
and strategic landscaping methods, and coaches utility companies on corporate
outreach and the development of citizen-based environmental activities.
32
image:
The Benefits of Urban Trees
corroborate the previously mentioned field
measurements. These simulations pre-
dicted that increasing the tree cover by 25
percent in Sacramento and Phoenix would
decrease air temperatures at 2 p.m. in July
by 6 to 10°F (Figures 2-7 and 2-8).
Evapotranspiration and Energy Use
Researchers at LBL have also used
computer simulations to study the com-
bined direct and indirect effects of veg-
etation on the energy use of typical one-
story buildings in Sacramento, Lake
Charles (LA), Phoenix, and Los Angeles.
In these simulations, the effects of trees
on building energy use were categorized
either as direct effects due to shading and
wind shielding or indirect effects due to
evapotranspiration. The effects of 10
percent and 25 percent increased vegeta-
tion cover (corresponding to one and
three trees per house) were simulated
first separately, to test the contribution
of each effect, and then in combination,
to yield comprehensive, more realistic re-
sults. Figure 2-9 summarizes these re-
sults. Because of the difficulty in simu-
lating the indirect effects of evapotrans-
piration, the results should be regarded
as more hypothetical than those shown
in Figures 2-3, 2-5, and 2-6.
In Los Angeles, the reductions are
small because the base cooling energy
use is relatively low (only 65 cooling
hours per year), and it is assumed that
natural ventilation is used whenever
possible. Therefore, the results for Los
Angeles have been omitted from Figure
2-9. A 10 percent increase in tree cover
in the other three cities (corresponding
to one tree per house), however, pro-
duced savings of 24 percent in Sacra-
mento and 12 percent in Phoenix and
Lake Charles, corresponding to dollar
savings of $40 to $90. The corresponding
Sacramento
100-
98
96
_ 94
U_
| 92
| 90
Q>
t 88
"86
84
82
78
Existing tree cover
10% additional cover
25% additional cover
10 12 14 16 18 20 22 24
HOUR
Source Huang et al , 1987
Figures 2-7.
Temperature reductions in Sacramento due to added tree cover on a typical
summer day in July, based on computer simulations
Phoenix
95
90-
85-
3 80-
I 75
70
65
60
Existing tree cover
10% additional cover
25% additional cover
~ \ i l l i l i i l i i l ] ll i l i i l i
2 4 6 8 10 12 14 16 18 20 22 24
HOUR
Source Huang et al . 1987
Figure 2-8.
Temperature reductions in Phoenix due to added tree cover on a typical summer
day in July based on computer simulations Increasing tree cover can significantly
decrease city-wide temperatures
33
image:
Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 2-9.
Estimated Coo/ing En-
ergy savings in a typical,
well-insulated, new
house from the com-
bined direct and indirect
effects of trees Note
that direct effects pro-
vide a relatively small per-
centage of the total en-
ergy savings for new
housing stock.
If we were to
plant 100 mil-
lion trees, and
implement light-
surfacing pro-
grams, we could
reduce our
electricity use by
50 billion kilo-
watt hours per
year (2 percent
of annual elec-
tricity use in the
United States),
and reduce the
amount of CO2
dumped into the
atmosphere by
as much as 35
million tons per
year.
300
250
200
150
WO
50
0
| Savings from Indirect Effects
I Savings from Direct Effects
17
Three trees per house
One tree per house
Sacramento Lake Phoenix
Charles
(LA)
' Percentages refer to savings of
total coo/ing energy use
Sacramento Lake Phoenix
Charles
ILA)
Source Huang et al , 1987
savings in peak electricity use vary from 9 percent in Phoenix to 20 percent in Sac-
ramento and Los Angeles.
A 25 percent increase in tree cover (corresponding to three trees per house) was
estimated to have an even more dramatic impact on summer cooling bills, with re-
ductions in cooling energy use of 57 percent in Sacramento, 17 percent in Phoenix,
and 23 percent in Lake Charles. The monetary value of these energy savings are from
$100 to $250 a year, per household.
According to this study, the direct effects of shading account for only 10 to 35
percent of the total cooling energy savings. The remaining savings result from tem-
peratures lowered by evapotranspiration. The ratio of these two savings is also affected
by how well a house is insulated and caulked. Older houses (which have a lower thermal
integrity) will show greater savings from shading than newer, tighter houses.
These simulated and measured findings indicate that trees can be of potential
benefit to the urban dweller if care is taken in positioning them. Trees can save both
heating and cooling energy use particularly if properly considered during the building
design stages.
Trees And The Greenhouse Effect
By reducing cooling energy use, trees do more than save residents money. They
also can help mitigate, even reduce, the greenhouse effect, which many scientists
think could cause widespread disruptions and dislocations in the next 100 years.
As discussed in Chapter 1, scientists now believe that if all 100 million urban
tree spaces were filled, and if rooftops and parking lots were painted light colors,
34
image:
The Benefits of Urban Trees
we could reduce our electricity use by 50 billion kilowatt hours each year, thereby
reducing the amount of CO2 dumped into the atmosphere by as much as 35 million
tons per year (NAS, 1991). Scientists call this benefit "avoided carbon." In addition,
trees absorb carbon dioxide for photosynthesis and store some of the carbon. This
process, called "sequestering," helps mitigate the amount of carbon dioxide emitted
by power plants when they generate power for air conditioning. Figure 2-10 illustrates
the cycle of potential carbon sequestering by trees.
Rural Versus Urban Trees
One obvious question that comes up when we talk about planting trees—whether
to reduce energy costs or the amount of carbon dioxide in the atmosphere—is "why
not plant trees in rural areas?" After all, there are more spaces for trees in the coun-
tryside than in urban areas, and rural conditions support tree longevity far more than
do urban conditions.
It's actually not an either/or question. Both urban and rural planting programs have
benefits. For heat island mitigation and global warming reduction, however, urban trees
are far more efficient.
A tree planted in the countryside sequesters CO2 from the atmosphere. A tree
planted in the city also sequesters CO2, yet its cooling effects have an additional ben-
efit: by shading and reducing air temperatures around buildings, it reduces the need
for air conditioning, thereby reducing the amount of CO2 dumped into the atmosphere
Trees absorb
CO2 directly
Burning
fossilfael
produces CO2
Trees
reduce (fl2
bycuiting
energyuse
Figure 2-10.
Trees can help reduce the
greenhouse effect in two
ways First, trees directly
absorb CO2—the primary
greenhouse gas—from
the atmosphere during
photosynthesis. Second,
shade from trees can re-
duce air-conditioning en-
ergy use, which reduces
the amount of CO2 emit-
ted by power plants.
Source Adapted from American Forestry Association
35
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
at the power plant. Indeed, the annual amount of carbon saved per tree from cooling
energy savings (88 pounds saved per tree per year) is five to ten times greater than
the amount of carbon sequestered on a per tree basis.1
Researchers have developed indicators such as the "Cost of Conserved Energy"
(CCE) to compare the potential savings in energy conservation with the cost of the
investment. To establish these costs (which are expressed in dollars per kilowatt
hour), researchers divide the annualized cost of a conservation measure by the annual
energy savings.
Researchers use a similar formula to calculate the Costs of Conserved Carbon
(CCC). To make this calculation, researchers divide the cost of conserved energy
by the amount of carbon burned in a power plant to generate one kilowatt hour of
electricity. The result is expressed as dollars per ton of carbon.
In fact, if enough trees are planted, we can reduce our cooling energy use enough
to avoid the costly and unsightly construction of new power plants and the burden
of their economic, social, and environmental costs. See Appendix B for a more detailed
discussion of calculating these costs and efficiency measures.
On a carbon
savings basis
alone, urban
trees provide
greater benefits
than rural trees,
because they
reduce carbon
emissions by
reducing cooling
energy consump-
tion. Research-
ers estimate that
an urban tree
can save five to
ten times more
overall carbon
than a rural
tree.
Using Trees To Reduce Urban Air Pollution
The air in many of America's larger communities fails to meet air quality standards
much of the time, although many communities have made significant improvements
in recent years. In Los Angeles, the air was classed as "unhealthful" about one-third
of the time in 1979: this was down only 100 to 110 days a year by 1983. In New York
City, unhealthful air was recorded over 150 days in 1979 and dropped only to 80 in
1983. Clearly, in spite of intensive efforts and pollution control, the quality of the
urban community as human habitat remains threatened by air pollution.
This is a complex problem that demands considerable attention. But there is a
role here for trees, as well, in addition to reducing energy use and CO2 emissions,
trees act as free-standing air purifiers.
Tree leaves and needles precipitate significant amounts of particulates from the
air. One researcher estimates that a street lined with healthy trees can reduce air-
borne dust particles by as much as 7,000 particles per liter of air (Bernatsky, 1978).
In addition, some nitrogen oxides (NO and NO2) and airborne ammonia (NH3) can
be taken up by foliage, with the nitrogen going to plant use. Trees can also utilize
some sulfur dioxide (SO2) and ozone (O3), but many species suffer severe damage
from exposure to high concentrations.
Most of the pollution reduction ability of trees is, however, finally related to
the soil, since pollutants are either washed to the ground from leaf surfaces or fall
directly as the result of having collided with tree structures or entering wind eddies
caused by the vegetation. The ability of soils to neutralize pollutants and prevent
subsequent water contamination varies considerably. Species and sub-species of trees
also vary in their sensitivity to different pollutants. Some handle high pollution levels
'The estimated average carbon savings of 88 Ibs. carbon are the product of the energy savings per tree
(220 kilowatt hours) and the number of pounds of carbon saved per kilowatt hours (.44 pounds)
36
image:
The Benefits of Urban Trees
reasonably well; others serve as sensitive indicators of the degree of environmental
deterioration.
Thus, it is possible to utilize trees and other vegetation as part of a pollution re-
duction scheme, but only within limits. Such a strategy cannot replace efforts to reduce
pollution at its source. Where trees and forests have been stunted or killed by pollution,
the basic environmental life machine has been reduced in capacity, and all life on
earth is affected by this change.
Trees And Urban Noise
Trees also filter another type of pollution: urban noise. This is a pervasive and
troublesome feature of the urban environment. Trees can be a significant factor in
reducing unwanted sound levels. The leaves, twigs, and branches absorb sound, par-
ticularly high frequency sounds that are the most bothersome to humans. Indeed,
a belt of trees 98 feet wide and 49 feet tall has been shown to reduce highway noise
by 6 to 10 decibels—a sound-energy reduction of almost 50 percent.
In addition to reducing unwanted noise, trees produce alternative sounds that
can "mask" other noises and make them less noticeable. With the wind rustling through
leaves and with birds singing, the drone of a nearby freeway is less noticeable and
less bothersome.
Psychological Benefits Of Trees
While it is difficult to quantify what philosophers, naturalists, and theologians
have been telling us for centuries about the soothing aspects of natural landscapes,
enough research has been done to prove that a qualitative effect does exist. That is,
Figure 2-11.
Benefits of berm A row
of trees can be particularly
effective in screening un-
desirable urban noise
37
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 2-12.
Researchers have found
that trees in urban areas
can significantly enhance
our sense of well-being.
trees significantly reduce that familiar feeling of being severely stressed, while they
increase feelings of peace and well-being.
A number of researchers have examined the effects of trees on emotional states.
Roger Ulrich, the Associate Dean for Research at Texas A&M University, for instance,
studied subjects' reactions to color slides of rural scenes and urban scenes. He found
that subjects were more interested in, and felt more positively about, the rural scenes
than urban ones. Ulrich also recorded the subjects' brain alpha waves (which have
been correlated with feelings of relaxation) during the slide presentation. Alpha am-
plitudes were higher when subjects saw rural scenes than when they saw urban ones.
A number of studies also have linked recreation in nature areas to psychological
well-being. One study found that visitors to Chicago's Morton Arboreteum associated
feelings of peacefulness, quiet, and tranquility with their stay. Similarly, research
has found that the mostly low-income, inner-city dwellers visiting Detroit's Belle
Isle Park experienced significant stress reduction. Finally, one study had encouraged
subjects to spend 40 minutes walking in an urban area with trees, 40 minutes walking
in a denuded urban area, or 40 minutes relaxing with magazines and music. Those
subjects who walked under the trees reported more positive feelings than did those
doing other activities.
In a more recent study, Ulrich first showed 120 subjects a stressful movie and
then showed them one of six different videotapes of urban and natural settings. As
the subjects watched the tapes, researchers took readings on their heart rates, muscle
38
image:
The Benefits of Urban Trees
tension, skin conductance, and pulses. Both psychological self-ratings and the
physiological measurements showed that subjects recuperated from the stressful movie
more rapidly, and more thoroughly, with exposure to natural settings.
Physiological benefits related to trees can be equally striking. One study of hospital
patients recovering from surgery found that individuals had shorter post-operative
stays, fewer negative evaluative comments in nurses' notes, fewer post-surgical com-
plications, and fewer painkillers needed when they saw trees from their window, rather
than a brick wall. Similarly, prisoners with cell window views of nature had fewer
stress syndromes (including head-aches and digestive upsets) than those looking at
buildings or other prisoners.
Wildlife And Recreation
It is a well-documented fact that humans seek forested areas for recreation. What
is less well understood is that, for many of America's urban residents, the most im-
portant recreational forest (either by choice or necessity) is the forest that is around
them every day.
Forest and park managers are faced with the fact that not all people want or need
the same kind of experiences. A study by researcher J.F. Dwyer found that people
in downtown Chicago preferred more intensively developed and managed parks as
a location for visiting and other social interaction, while suburbanites wanted more
natural, undeveloped areas to "get away from people."
One of the major attractions of either kind of forest is wildlife. Trees may provide
colors, shapes, sounds, and other sensory pleasures, but wild animals provide the
animation that particularly delights most forest visitors. From the ubiquitous gray
squirrel and pigeon of the central city to the shy deer or rabbit of the greenway,
people enjoy watching the wildlife that characterizes trees, forests, and their sur-
rounding environs.
Water Quality And Hydrology
Trees intercept falling raindrops and moderate their passage to the ground. Runoff,
erosion, and flooding during intensive rainfall can be significant problems in an en-
vironment largely dominated by concrete, asphalt, and rooftops, and lacking the mod-
erating canopy of trees. Water flows concentrated by impervious surfaces hit un-
protected soils or stream channels with terrific force, causing accelerated soil erosion
and significant water pollution along with very high flood flows. Trees that shelter
impervious areas can cut the rate at which water hits the surface, and tree roots can
provide protection that slows water flows and reduces soil erosion. Gary Moll, urban
forester at the American Forestry Association, estimates that a city with 30 percent
tree cover has a leaf and branch surface area that adds up to four times as much in-
tercepting surface as provided by the city's buildings and concrete. As a result, cities
with maximum tree cover can experience significant reduction of peak flood flows.
This translates into less construction cost and land dedicated to floodways and storm
sewers, less instances of overflow and resulting damage to life and property.
39
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
It also results in less pollution flushed into rivers, lakes and estuaries—pollution
which can eradicate important economic fisheries, destroy recreational opportunities,
and even poison the drinking water supplies of millions of people. These problems
can almost always be traced to the use and management of the land in the water-
shed. If that land is urbanized, the existence and condition of its trees will have a
significant impact on the condition of the watershed.
Forested areas in urban regions may also become significant in waste-water treat-
ment. Partially treated urban wastewater has been sprayed on forest lands with good
effect in several cities. This not only provides a least-cost way of providing ter-
tiary water treatment, but also has beneficial effects on forest productivity, aquifer
recharge, and stream flow. In State College, Pennsylvania, for example, a number
of researchers have reported that 16 years of spraying partially treated sewage on
a forest watershed did not contaminate groundwater, but did return 90 percent of
the water to the aquifer. Different forest ecosystems, different soils, and varying
aquifer characteristics need be factored into such a program, and intensive monitoring
is needed to assure that performance is meeting health standards. But this method
of waste-water treatment is almost certain to appeal to more and more communi-
ties as water supplies get scarcer and conventional waste treatment facilities be-
come more expensive to operate.
Conclusion
Trees save energy by shading, wind-shielding, and evapotranspiration. But they
shouldn't merely be seen as green air conditioners. Trees also help mitigate the green-
house effect, filter pollutants, mask noise, prevent erosion, and calm their human
observers. These are all benefits that air conditioners simply cannot provide. In ad-
dition, trees and shrubs enhance our environment, provide recreation for our children,
and through group planning and planting, can sponsor a feeling of community within
neighborhoods.
Indeed, people all over the country have begun planting trees, not just for energy
conservation, but for all these other reasons as well. In cities ranging from Atlanta
to San Francisco, and Chicago to Los Angeles, people are planting trees both near
their homes and in their neighborhoods. Planting for energy conservation can easily
become a part—or the foundation—of such efforts.
Few cities have implemented urban forestry programs for the sake
of energy conservation. Those cities which have done so, however, have
had high rates of success. In Nanjing, China, for instance, after 34 million
trees were planted in the late 1940s, average summer temperatures
dropped 5°F. Similarly, fingers of green open space convey cool night
air into downtown Stuttgart, in West Germany, and help reduce day-
time temperatures.
40
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The Benefits of Urban Trees
The Trees for Tucson/Global Releaf reforestation program proposes
planting 500,000 desert-adapted trees before 1996. An economic-ecological
model calculated the costs and benefits associated with the program.
The computer simulation accounted for planting locations, planting rates,
growth rates, and mortality rates when projecting average annual benefits
and costs. Costs modeled included planting, pruning, tree removal, and
irrigation water. Benefits accounted for include cooling energy savings,
and avoided dust and stormwater runoff costs. The simulations do not
include the effects of trees on property values (generally considered to
be positive), aesthetics, wildlife habitat, human stress, nor on factors
that are not local.
Projected net benefits are $236.5 million for the 40-year planning
horizon. The benefit-cost ratio and internal rate of return of all trees are
2.6 and 7.1, respectively. Trees planted in parks are projected to pro-
vide the highest benefit-cost ratio (2.7) and trees along residential streets
the lowest (2.2). Tree removal costs are the most important manage-
ment expense and energy savings for air conditioning provide the greatest
benefits (attributed mostly to house or "yard" trees). Average annual
cooling energy benefits per tree are projected to be 227 kWh ($16.34)
for evapotranspirational cooling and 61 kWh ($4.39) for direct shade. Ninety-
seven percent (464 Ib.) of the total carbon conserved annually per mature
tree is attributed to reduced power plant emissions.
• Park Benefits B Yard Benefits D Street Benefits
D Park Costs • Yard Costs ^ Street Costs
1993 1998 2003 2008 2013 2018 2023 2028
Year
Source McPherson, 1991
Figure 2-13.
Projected annual costs and benefits of the Trees for Tucson/Global Releaf reforestation
program.
41
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 2-14.
Consider the seasonal
path of the sun when
planning landscaping
improvements. Strategic
placement of deciduous
trees on the southwest
and west sides of a build-
ing can help maximize
the cooling effects of
shade in summer and can
allow sunlight to reach
the building in winter
^^
Source Missouri Natural Resources Department (Koon, 1989)
Further Reading
There have been numerous studies on the wind-shielding and shading effects
of trees by Heisler (1981, 1984, and 1986) and DeWalle (1983 and 1988). The mi-
croclimate effects of different amounts of tree cover have been measured by McGinn
(1982), Taha et al. (1988), Rainer et al. (1989) and Heisler (1989).
McPherson measured the effect of different landscaping treatments on building
energy use using scale models (1989). Computer studies of the energy savings from
the direct effects of trees were done by Huang et al. (1989) and McPherson et al. (1988).
Another study by Huang et al. (1987) modeled the indirect effects of tree evapotrans-
piration on temperatures and building energy use.
Two very informative books published on the subject of tree planting in urban
communities are: Shading Our Cities (Island Press, 1989) by Moll and Ebenreck, a
thorough discussion of urban forestry for both general and professional readers, with
guidelines for program development; and The Simple Act of Planting A Tree (Jeremy
P. Tarcher, Inc., 1990) by Lipkis and Lipkis, directed especially to citizens, also with
detailed guidelines for community programs.
42
image:
Hashem Akbari
Phil Martien
Arthur Rosenfeld
Using Light-Colored Surfaces
to Cool Our Communities
The practice of using light-colored surfaces to keep buildings and outdoor urban
areas cool is not new. In many tropical countries, particularly those with large
amounts of sunshine, the traditional architecture has many examples of light-colored
walls, roofs, and streets. In this country, architects and urban planners have overlooked
this energy-conscious design principle relying instead, on mechanical air conditioning
to maintain comfort during the summer months. Unfortunately, the dark-colored surfaces
commonly used here increase air-conditioning costs for individual houses—because
their walls and roofs get hot, and for all buildings in the city—because temperatures
of the entire area rise. Yet computer models of urban climates have shown that the
use of light-colored surfaces in cities can reduce air conditioning costs for everyone,
most often without additional cost.
Computer mod-
els of urban
climates have
shown that the
use of light-
colored surfaces
in cities can
reduce air-
conditioning
costs for every-
one, often with-
out additional
cost.
-J .
Figure 3-1.
Traditional light surfaces:
In sunny countries, such
as Greece, walls, roofs,
and streets have been
painted in light colors for
centuries.
Greek National Tourist Agency, 1990
43
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Studies done at
Oak Ridge
National Labo-
ratory in Ten-
nessee have
found that dark-
colored roofs
routinely exceed
160°F, on
summer days,
while surfaces
with flat white
paint reach
135°F and those
with glossy
white paint
seldom exceed
120°F.
Figure 3-2.
Surface contrast. Simply
changing the surface
colors of our urban com-
munities could signifi-
cantly decrease their
temperatures
Because no urban community in the United States or abroad has yet initiated a
formal program of albedo modification, we have no experience with successful imple-
mentation practices, potential drawbacks, and conflicts with other urban issues. This
chapter, then, is more theoretical, and less specific than those on tree planting, which
benefit from a wealth of programs and written materials. We would like to stress,
however, that our preliminary analysis indicates that the energy and environmental
benefits of albedo modifications are high, while the costs and potential risks can be
strikingly low.
What Is Albedo?
Urban landscapes consist of myriad surfaces, including building roofs and walls,
streets, freeways, parking lots, paved walkways, driveways, school yards, and play-
grounds. Each of these surfaces either absorbs or reflects a significant portion of the
sunlight falling on it. Scientists use the term albedo to define the ability of a surface
to reflect incoming solar radiation. The opposite of albedo is "absorptivity," or the
ability of a surface to absorb incoming radiation.
Albedo is measured on a scale from 0 to 1. A surface with a relatively high albedo
of 0.75 reflects most of the incoming solar energy, while one with a low albedo of
0.25 or 0.10 will absorb most of it.
Source Huang,1991
44
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Using Light-Colored Surfaces to Cool Our Communities
In general, light-colored surfaces have high albedo, and dark-colored surfaces
have low albedo. However, there are cases where a light-colored surface will absorb
so much near-infrared radiation that it will have a low albedo. Similarly, other surfaces
which appear quite dark to the eye, such as green grass, are good reflectors of infrared
radiation and have albedos from 0.25 to 0.30. Texture and geometry also affect a
surface's albedo. A complex, bumpy surface tends to absorb more radiation than does
a flat surface made of the same material. Figure 3-3 shows the albedo for a number
of typical urban surfaces.
Solar energy that is not reflected is absorbed by the surface (unless it allows the
radiation to penetrate, as water or glass do). That means that albedo directly determines
the effect solar radiation has on surface temperature. A light-colored surface with high
albedo will absorb less sunlight and remain cooler than a dark-colored surface of lower
albedo and similar thermal properties. Buildings with dark- or low-albedo surfaces will
tend to have higher air-conditioning loads, because the heat from the hot walls and roofs
eventually seeps inside. Studies done at Oak Ridge National Laboratory in Tennessee
have found that dark-colored roofs routinely exceed 160°F on summer days, while
surfaces with flat white paint reach 135°F, and surfaces with glazed white paint seldom
exceed 120°F. Similarly, on a 90°F day, the surface temperature of asphalt can reach
140°F (See Figure 3-4). This can increase air temperatures by 5°F and more. Figure
3-5 shows that during the summer, light-colored surfaces are, on average, 15°F cooler
than dark-colored ones.
Modifying the albedo of a building will lower the heat build-up from sunlight
on the walls and roofs, and reduce the amount of electricity needed for air conditioning.
Computer simulations of a typical house in Sacramento, California indicate that its
Tar & Gravel
White Paint 0.08 - 0.18
0.50 - 0.90
Highly Reflective
Roof 0.60 - 0.70
Figure 3-3.
Surface albedo values
The more solar radiation
a surface absorbs, the
hotter it gets The more
radiation it reflects, the
cooler it stays Today's
urban communities con-
tain surfaces with many
different albedo values
Surfaces with high albedo
values reflect more solar
radiation and are gener-
ally cooler.
Source Huang and Tana, 1990
45
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 3-4.
Daily surface tempera-
ture' Dark-colored roofs
get much hotter through-
out the day than do light-
colored roofs.
Effects of Surface Color on Temperature
1
0 12 0 12 0 12 0 12 0 12 0 12
120
100
80
60
Source Adapted from Gnggs et al , 1989
total air-conditioning bill can be reduced by up to 20 percent if the albedo of the
roofs and walls are increased from a typical 0.30 to a light-colored 0.90.
We call this kind of energy saving from albedo modifications "direct savings,"
since they relate solely to the individual house. If similar albedo modifications are
implemented on a large number of urban surfaces, the collective albedo of a neigh-
borhood or city will be changed and the air temperatures lowered as a result. This
will then reduce the amount of cooling energy needed for all houses in that city or
neighborhood. These are "indirect savings."
In general, changing the albedo of a building produces direct savings only for
houses, single story industrial buildings, or small commercial buildings. Changing
the albedo of large buildings will not produce significant direct savings because they
have small surface-to-volume ratios and tend to generate a lot of internal heat.
However, even large buildings will realize significant indirect savings from city-
wide albedo modifications. That is, while large buildings do not gain direct savings
from increasing albedo, they do gain indirect savings from the generally lowered
temperatures produced by wide-scale reductions in albedo.
Will Changing Surface Colors Save Energy?
Many studies exist which show that increasing surface albedos lowers surface tem-
peratures. To date, there is little measured data on the direct energy savings from changes
in building albedo. Measurements of the indirect energy savings from large-scale changes
in urban albedo are, for obvious reasons, even more difficult and have not been at-
tempted. However, both the direct and indirect effects can be estimated using computer
46
image:
Using Light-Colored Surfaces to Cool Our Communities
120
100
Patch No. Surface
Dark
Light
Bare
Short grass
Long grass
1
2
3
4
5
Air
Figure 3-5.
Year-round ground sur-
face temperatures: Dark-
colored surfaces are also
hotterthroughoutthe year
than light-colored sur-
faces or even ground veg-
etation.
Source Kusuda, 1971
programs that model building energy use and urban climate conditions. These show
that increasing the albedo of urban surfaces can significantly reduce both energy con-
sumption for individual buildings and the outdoor temperatures of cities.
For example, researchers at Lawrence Berkeley Laboratory have used a detailed
computer program to simulate the energy use of a typical one-story ranch house in
Sacramento, California, with an average albedo of 0.25, roughly equivalent to grey
walls and a dark-shingled roof. When they increased the wall albedo by 0.13 (painting
the walls off-white for instance), the amount of energy needed for cooling dropped
by 2.7 percent. When they increased the building's albedo by 0.60, by perhaps using
a light-colored shingle roof, its cooling energy use dropped by almost 19 percent.
47
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A Guidebook on Tree Planting and Light-Colored Surfacing
In a poorly
insulated house,
such as those
built before
1970, increased
albedo could
reduce cooling-
energy use by 5
percent for each
0.01 increment
in albedo. For
better insulated
houses like
those built
today, increased
albedo can
reduce cooling-
energy use by 3
percent for each
0.01 increment
in albedo.
Figure 3-6.
Cooling energy savings
from the direct effects of
increased albedo Com-
pu ter models project sig-
nificant energy savings
from albedo increases in
cities all across the coun-
try Note higher dollar
savings in sunbelt cities.
In other computer simulations, researchers found that the energy savings from
increased albedo are much larger for poorly insulated houses, as insulation helps to
block the heat from the outside surfaces. They simulated both poorly and well-insulated
houses, with an initial albedo of 0.30, and then increased it by 0.40. In the poorly
insulated house, cooling-energy use dropped by 11 to 22 percent. In the well-insulated
house, cooling-energy use dropped by 8 to 13 percent. Although the total savings
are two times larger for the poorly insulated house, they are significant even in the
well-insulated house (See Figure 3-6).
Albedo also has indirect effects. These seem to be larger than the direct ones.
An urban climate model has been used to simulate how changing a city's collective
albedo affects air temperature. The results showed that the indirect cooling energy
savings for typical houses could be 3 percent to 5 percent for each 0.01 increase in
overall city albedo. In a poorly insulated house, such as those built before 1970, in-
creased urban albedo can reduce the cooling-energy use by 5 percent for each 0.01
increment in albedo. For better-insulated houses like those built today, increased albedo
can reduce cooling-energy use by 3 percent for each 0.01 increment in albedo.
Researchers have also found that the albedo of a typical U.S. city can be increased
realistically by up to 0.15. Based on computer simulations, this albedo increase will
reduce a city's air temperature by 5°F, which, in turn, would produce indirect energy
savings of around 40 percent. When the direct and indirect savings of albedo changes
are combined, the simulated total energy savings approach 50 percent during average
hours and 30 percent during peak cooling periods.
Direct Cooling Energy Savings from Increased Albedo
Savings
($/year)
250
Minneapolis Pittsburgh Chicago Washington Sacramento Miami Phoenix
| OLD HOUSES
I NEW HOUSES NOTE: Percentages indicate savings of total energy cost
Source Taha, 1988
48
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Using Light-Colored Surfaces to Cool Our Communities
On a national level, researchers estimate that increased albedo can save annually,
in residential and commercial building, 22 billion kilowatt hours (0.25 quads), with
annual monetary savings over $2 billion. This estimate assumes that only half of the
surfaces in a typical city are available for albedo modifications.
How Much Will Albedo Modifications Cost?
Albedo programs can be implemented at little cost, because they can be incor-
porated into routine maintenance schedules and budgets. While no model programs
have been implemented so far, extrapolations from individual buildings show that
increasing albedo can be an extremely cost-effective strategy for reducing summer
electricity usage on a city-wide scale.
As mentioned before, changing albedo in the course of routine maintenance is very
cost effective, since in many cases it may cost nothing extra at all. Researchers estimate
that the Cost of Conserved Energy (See Appendix B) for repainting and resurfacing
is between 0 and 6 cents per kilowatt-hour. This compares quite favorably with the
cost of peak power residential electricity, which is about 10 cents per kilowatt-hour.
Potential Problems With Albedo
Perhaps the greatest problem with albedo modification at this time is that no
community or institution has initiated a program yet. Computer models can make
worthwhile estimates of the energy and environmental benefits of albedo modification,
but they cannot hypothesize about the potential problems of such programs. And, because
of the paucity of materials, a number of researchers have challenged the viability of
albedo modification, based on questions of soiling, glare, and citizen cooperation.
Will Light Urban Surfaces Cause Too Much Glare?
Some researchers worry that lightening the color of a city's streets and buildings
will cause uncomfortable glare for city dwellers. There are no reports, however, of
residents complaining about too much brightness in Mediterranean and Middle East
cities, many of which have predominantly white surfaces. It may also be possible
to develop materials that create less glare than those currently available.
Similarly, some researchers have questioned whether traffic markings on lightened
streets would be as visible as those on dark roads. Researchers at LBL, however,
believe that new marking designs (perhaps a dark median strip with traditionally white
markings) can be developed to ensure public safety.
Will Light Urban Surfaces Soil Too Quickly?
On the other end of the spectrum, some question exists as to the durability of
white surfaces, especially under the wear and tear of weathering and soiling. In some
parts of the country, for instance, light-colored roofs may discolor from leaves, tree
secretions, and air-borne dust and dirt. In that case, even a high-albedo roof would
become a low-albedo roof in a matter of time, thereby mitigating both the energy
and aesthetic benefits of the original conversion. Studies done at Oak Ridge National
49
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Figure 3-7.
Residents of cities in
tropical and mediterra-
nean areas have white-
washed their buildings
for centuries, sometimes
repainting outside walls
annually to ensure com-
fort Today, we can look
to that example to learn
how to cool our cities
and save energy, with a
method that is both aes-
thetically pleasing and
easy to implement
Laboratory, however, have shown that even soiled, highly reflective roofs have a higher
albedo than dark roofs.
Weathering from the oil drippings and tire scuff marks of vehicles could pose
more serious problems for light-colored streets. Again, while no studies have been
done on this potential issue, common sense observations of currently existing concrete
roads show that the soiling does not significantly alter the surface color. If we move
to lighter surfaced asphalt, we may want to lighten the color of auto tires as well.
Will Light Surfaces Increase Heating Bills In The Winter?
If light-colored surfaces reflect solar radiation, we may lose in the winter by paying
increased heating bills, even as we gain in the summer when cooling bills drop. Except
for computer simulations, no researchers have investigated, in a carefully designed
50
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Using Light-Colored Surfaces to Cool Our Communities
experiment, whether or not changing surface colors will result in a net benefit or
net cost on an annual basis. This is an issue primarily for areas subject to cold
winters, however. Areas where air conditioning is used most of the year will benefit
from light-colored surfaces because the cost of that space cooling will be kept
down throughout the year.
Will Citizens Resist Changing Surface Colors?
One final question that arises in the course of discussions on albedo modification
is "How will we convince citizens that this is an appropriate measure?" Questions
of implementation—including citizen action and ordinances are discussed in Chapter
7 of this guidebook.
How Can We Implement Urban Albedo Modification Programs?
Just as some states have building energy standards that specify minimum re-
quirements for window shading, awnings and shades, it is also possible to stipulate
minimum albedo values for building surfaces such as roofs or walls, or to give energy
credits or tax rebates for using materials with high albedos.
Different approaches are needed to promote high-albedo materials, depending
on whether it is private or public property. For private property (such as homes
or commercial property), the best approach is probably a combination of public
information, energy credits, or ordinances. Specifically, we recommend that com-
munity officials, school districts, and materials manufacturers:
1. Promote greater awareness of the potential for energy conservation in the se-
lection of building materials and surface colors.
2. Provide information to the public on the albedo (reflectivity) of different
building products.
3. Increase awareness among financiers, developers, and homeowners of the lower
operating costs, energy savings, and greater return on investment possible from
lightening surface colors.
We also recommend that professional schools and other educational programs
incorporate these principles in the training of builders, engineers, architects, city
planners, and urban and landscape designers.
For public property, such as roads or sidewalks, the approach should be to con-
vince the responsible city departments and school districts of the costs and benefits
(financial and environmental) in the use of alternate materials with higher albedo.
Finally, considerably more technical research needs to be done in order to:
1. Gain a better understanding of the feedback mechanism of large-scale al-
bedo modification.
2. Document existing urban albedos in various cities by combining data on land-
use patterns with those on the albedo of various urban surfaces.
3. Study the long-term albedos of building materials under typical urban conditions
to account for wear and urban grime.
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4. Evaluate the trade-offs between reductions in cooling energy use and possible
increases in heating energy costs with the use of light-colored surfaces.
See Chapter 7 for suggestions on developing ordinances and other legislation.
^^
Further Reading
As we discussed in the text, no formal albedo modification programs have been
implemented to date. Therefore, there is a dearth of measured data on the energy
savings from albedo changes, particularly as related to indirect effects of neighborhood-
wide albedo programs.
There have been, however, a number of technical studies documenting the re-
lationship between surface temperatures to the surface color and texture by Kusuda
(1971), Givoni (1981), and Griggs (1989). Computer studies of the impact of albedo
changes on building energy use were done by Taha et al. (1988). Studies of the overall
albedo of the urban landscape were done by Myrup (1972) and Aida (1982), while
Reagan (1979) measured the albedo of typical building materials. Practical information
on building and road materials can be found in trade journals, including Concrete
Construction, American City and Country, and publications of the Asphalt Institute,
in Maryland. In addition, much of the information on material availability and viability
can be obtained by directly contacting manufacturers in this country and abroad.
52
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Jane Arey
Roger Atkinson
Karina Garbesi
Bruce Nordman
Implementation Issues:
Water Use, Landfills, and Smog
Widespread tree planting has a number of beneficial effects, including shading,
conserving energy, reducing pollutants in the atmosphere, enhancing visual
appeal, and sequestering carbon dioxide. Such a program can also raise questions—
and potential problems—for the communities involved.
Several questions that may arise in the early planning stages of heat-island
reduction include whether tree planting programs conflict with water conservation
programs, whether trees pollute, and whether they create municipal solid-waste
problems. Much research remains to be done on these issues. The following dis-
cussions, however, will give policymakers some guidelines for their own analyses.
Will Urban Tree Planting Waste Valuable Water?
As discussed in previous chapters, trees can help reduce energy used for cooling
in buildings, both by shading and evapotranspiration. In recent years, increased public
awareness of these benefits, coupled with concerns about the environment, have led
to numerous proposals to plant trees. The American Forestry Association, for example,
has proposed planting 100 million trees in U.S. cities in its Global ReLeaf Cam-
paign. Similarly, in October of 1988, the Mayor of Los Angeles announced a proposal
to plant two to five million trees in the city.
Trees, however, need water to survive, and ground water can be a scarce resource
in arid communities such as in the West or Southwest.1 Planners and residents in
these communities may be concerned that tree programs will increase water use, and
that the costs and burdens of this increase will override energy benefit. Similarly,
it may appear that tree planting programs tailored to arid climates will reduce water
usage—which is good—but simultaneously will reduce cooling from evapotrans-
piration and thereby reduce its beneficial effect.
1 While no clear distinction has been made in this chapter between groundwater and city water generally
speaking, however, it concerns only groundwater.
With proper
landscape design,
residents can
save both water
and energy.
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Tree planting
need not always
result in in-
creased water
use. Appropri-
ate landscaping
strategies can
actually reduce
water use, even
as the amounts
of shade or
vegetation cover
Is there a trade-off between energy savings and water use in arid urban areas?
Urban environments are too complex to expect precise calculation of landscape water
usage and its effects on urban climates. It is possible, however, to estimate the relative
water usages of different landscape scenarios. It is also possible to identify planting
strategies that maximize cooling energy benefits while minimizing water consumption!
Research shows that residents can save water and energy with proper landscape design.
Landscaping In Arid Climates
Early settlers in the American Southwest tried to mold their new environment
in the image of the lush green landscapes of Europe and the Eastern seaboard. Planted
in the dry and desert regions of the West, however, these imported landscapes of
deciduous trees and green lawns created a large demand for water. With popula-
tion increasing and the specter of water shortage looming ever closer, a new trend
is emerging. This trend emphasizes replacing imported "artificial" landscapes with
native ones that use less water and are more in keeping with local climates and water
availability.
Many cities now have ordinances that encourage water-conserving landscapes.
Some water districts even offer cash incentives to homeowners who replace high-
water-use landscapes with low-water-use ones, or with gravel. In Arizona, local gov-
ernments use landscape ordinances to comply with a state law to eliminate groundwater
overdraft. The city of Mesa offers a $231 rebate if 50 percent of the total landscaped
area is covered with inorganic mulch, such as decomposed granite. Similarly,
California's Urban Water Management Act of 1983 pressures water retailers to conserve
water. The Act emphasizes landscape water conservation, because landscapes consume
30 to 50 percent of residential water. In fact, the state is counting on landscape water
conservation to help meet future water demands in the state.
Many landscape water conservation programs are already under way. Of 166 water
retailers responding to a questionnaire by the California Department of Water Resources
in 1986, at a local level, 39 percent had existing landscape-water conservation programs
and 23 percent had proposed programs. The North Marin Water District, for example,
in northern California, offers $50 for each 100 square feet of lawn removed and re-
placed with water-conserving plant materials.
The existence of such policies suggests a strong institutional resistance to tree
planting programs that threaten to increase landscape water use. It is important to
point out, however, that tree planting need not always increase water usage. Indeed,
appropriate landscaping can actually reduce water use, even as the amounts of shade,
or in some cases, total vegetation cover, increases.
Estimating Urban Water Needs
A number of factors must be considered when estimating the effect that tree
planting programs will have on urban water use. First, which elements of the landscape
will be displaced by the trees? If trees are planted in parking lots, for instance, their
influence will be much different than if they replace lawn areas. Second, will the
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Implementation Issues: Water Use, Landfills, and Smog
trees replace or supplement existing vegetation. That is, the water use of an area in
which trees replace lawn will be different than that in which trees are added to lawn.
In a recent study by researchers at Lawrence Berkeley Laboratory, urban vegetation
was divided into three broad classes: turf (or lawn); trees and palms; shrubs and
groundcovers (referred to simply as "turf," "trees," and "shrubs"). Based on available
data on the water use of other plants, each class received a "typical water use" rating.
Changes in urban landscape water use were estimated by simulating changes in the
amount of area covered by each vegetation class. The calculations, assumptions, and
methodology of the simulation are discussed in detail in Appendix C.
Trees, Shrubs, And Grass: Which Uses More Water?
LBL researchers found, and landscapers agree, that, in general, lawns use more water
than trees, and trees more water than shrubs and groundcovers (See Figure 4-1).1
The lower water usage of trees means that if trees replace grass, landscape water
requirements typically will decrease. If shrubs and groundcovers replace trees, still
more water savings can occur (See Figure 4-2). In this case, however, energy savings
will decrease, because these vegetations provide less shading for cooling.
Researchers
have found that
turf generally
uses more water
than trees, and
trees use more
water than
shrubs or
groundcovers.
Water Usages For Different Landscape Scenarios
The ways in which changes in landscapes affect water use were estimated be-
ginning with a base case scenario, in which grass occupied 13 percent of the total
urban area, trees took up 10 percent, and shrubs took up 4 percent. (This made a total
vegetated area of 27 percent, as was the case in Los Angeles in 1986.) Scenarios were
developed by modifying the landscape three ways. First, the total vegetated area
remained constant, but lawn area was replaced with varying amounts of trees and
shrubs. Second, the total vegetated area was increased, while varying the areas of
lawn, trees, and shrubs. Finally, lawn area was reduced by replacing it with drought-
adapted trees and shrubs, thereby simulating low-water-use practices, also called
"Xeriscape." The following examples illustrate these scenarios.
Replace lawn area with typical trees and shrubs. In this scenario, the total
vegetated area remains the same. But the area covered by trees is doubled (to 20 percent
of the total urban area), the area covered by shrubs stays the same, and the lawn area
is reduced from 13 to 3 percent. In this case, water use actually decreased by 18
percent. That means that in the hypothetical city of the study, water use could decrease
by 18 percent, while doubling tree cover to replace existing lawn area.
Increase total vegetated area, while varying the relative cover of lawn, trees,
and shrubs. In this scenario, the total vegetation cover increases from 27 to 33 percent
by doubling the tree and shrub cover, and reducing the lawn area from 13 to 5 percent.
Watering trees at the same level as grasses can harm them in some cases. A joint report by the
Municipal Water District of Orange County and the Department of Landscape Architecture at Cal
Poly University revealed that the average lifespans of 44 tree species in Southern California were
shortened by 58 percent when planted in lawns For one drought-adapted species of Eucalyptus
(red iron bark), the estimated tree lifespan in a lawn was reduced by 90 percent.
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Relative water usage of different types of plants
4 4
grass
shrubs and
groundcovers
trees
Figure 4-1.
Estimated typical water usage of varying plant types in relative amounts' The
amount of water needed by plants vanes with location and climate. Generally,
lawns use more water than trees, and trees use more water than both shrubs and
groundcovers
Source McPherson and Sacamano, 1989
Figure 4-2.
Water consumption and turf Extensive turf area consumes more water than turf
area combined with groundcover
This would be the case, for example, in
a planting program in which shade trees
are planted near houses, and some lawn
areas are replaced with trees and shrubs.
In this case, landscape water use stayed
the same. When typical trees and shrubs
are used to expand the amount of total
vegetation, landscape water use increased.
Xeriscape (minimize lawn area and
use low-water-use trees and shrubs). In
this scenario, low-water-use trees, shrubs,
and groundcovers replace the total veg-
etated area, which is expanded from 27 to
47 percent, by tripling tree cover, more
than doubling shrub cover, and reducing
lawn area from 13 to 7 percent. Even with
this increase, water use was held constant.
But when total vegetation area increased
to 33 percent of the total urban area (by
doubling tree and shrub areas, and re-
ducing lawn area to 5 percent), water use
was reduced by 30 percent.
In identical distributions, low-water-
use plants save 20 to 43 percent of the water
used by typical plants. This is in keeping
with the results of landscaping studies on
Xeriscape design (low-water-use landscap-
ing) which show savings of as high as 50
to 60 percent over traditional designs.
Multi-layered canopy (lawn shaded
by shrubs and trees). The most inter-
esting case of a multi-layered canopy is
that of lawn shaded by trees. In such a
case, we cannot simply combine the con-
tributions of tree and lawn, as if they were
on different plots of land, because the
shading of the lawn will modify its water
requirements. We found that on a hot,
sunny day, tree shade can reduce lawn wa-
ter requirements by as much as 95 percent.
In other words, even the combined water
use of tree and lawn can be lower than that
of an unshaded lawn.
Importantly, the numerical results of
both the study's vegetation distribution
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Implementation Issues: Water Use, Landfills, and Smog
model and its calculation of the water needs for a multi-layered landscape are rough
estimates, based on the assumed starting conditions of the models. In order to obtain
numerically meaningful estimates for a given location, appropriate initial conditions
must be used. For example, if an area starts with a lot of turf and high-water-use
trees, tree planting programs which replace lawn area and other high-water-use species
with low-water-use species are likely to reduce landscape water use significantly.
Areas which already have low-water-use species will not show large water savings.
Even the com-
bined water use
of tree and lawn
can be lower
than that of an
unshaded lawn.
Trees, Energy, And Water: Implications For Urban Temperatures
Any trees planted near occupied structures of modest height should mitigate
cooling energy needs in hot communities by shading. But it is the total landscaping
strategy which will determine if evapotranspiration increases or decreases, and, there-
fore, if the net evapotranspiration will lessen or increase the existing savings from
shading. That is, if water use by vegetation is increased, cooling is enhanced. If water
use decreases, the energy savings from evapotranspiration will also decrease.
The extent to which changes in evapotranspiration affect changes in near-ground
air temperature (and hence cooling-energy needs) depends on a number of factors,
including the density and geometry of the urban canopy (including buildings), wind
conditions, and temperature. The data are not yet available to back up such detailed
modeling of the urban climate system. It is impossible, therefore, to exactly calculate
the energy/water trade-offs. However, field experiments by E. Gregory McPherson
and his colleagues at the University of Arizona demonstrate that both water and energy
can be saved by planting low-water-use trees and shrubs around residences. This
indicates that the losses from reduced evapotranspiration do not seriously threaten
the benefits of trees and shrubs in dry cities.
Planning Ahead
It is clear from the analysis above that trees can be added to most urban landscapes
without increasing water use—if trees, or some combination of trees, shrubs, and
groundcover, replace lawn area. If total vegetated area remains constant, landscape
water requirements can decrease rapidly as trees replace lawns. As a result, tree
planting programs to conserve cooling energy are not only consistent with current
landscape water conservation programs, but ought to be an integral part of planning.
That is, we can save water, while we save energy, with proper landscape design.
Plant A Diversity Of Species
One word of caution: If we find—as is likely—that we need to choose low-water-
use species for our tree planting programs in arid cities, we should not repeat the
historical mistakes of agriculture and forestry. Too often, planners in these sectors
sought out and planted the single most effective species available. Unfortunately,
monocropping has proven highly susceptible to pest outbreaks—which could destroy
the positive economics of the planting program. Instead, we should maximize the
many other positive environmental benefits by planting a diversity of species.
On a hot, sunny
day, tree shade
can reduce lawn
water require-
ments by as much
as 95 percent if
the lawn is
entirely shaded.
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Optimize Benefits
In addition, any planting program should optimize benefits for wildlife, as well
as for people. Planting native species in arid areas not only assures the selection of
drought-adapted and low-water-use species, but provides food and shelter for local
wildlife. This approach can be aesthetically pleasing, as well as environmentally and
socially sound. Perhaps the best example of this approach is the extensive use of native
desert species in Santa Fe, New Mexico. This beautiful city appears to be a gentle
extension of the surrounding natural environment. It provides a sense of place for
the residents, and thereby engenders an appreciation of the native landscape.
Maintain A Regional Context
When assessing the benefits and costs of tree planting programs, it is important
to maintain a regional context. The initial distribution of vegetation in the region
must be accounted for, as well as the local cost and availability of both energy and
water. In some areas, like California, potential water savings in agriculture might
dwarf savings obtainable from urban landscaping. In such cases, water conserving
practices in agriculture might free up considerable amounts of water for urban land-
scapes and wild areas.
Tips on Low-Water-Use Landscaping
"Issues of water re-allocation are beyond the scope of the guidebook.
But they need to be considered in the long run. Here are two categories
of recommendations for low-water-use landscaping:
Immediate Actions
1) Plant low-water-use trees first next to one- and two- story buildings
(trees could also be used to shade larger structures by including
planting terraces on buildings with a pyramidal structure).
2) Replace lawn with trees where possible.
3) Plant low-water-use shrubs and groundcovers where vegetation
is desired.
4) Use native plants where possible to provide food and habitat for
native wildlife.
5) Include natural shading in building energy codes.
Future Actions
1) Create greenways connecting parks using native vegetation, thereby
providing migration corridors for wildlife and hiking opportunities
for residents.
2) Consider sectoral reapportionment of water from agriculture to
urban areas.
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Implementation Issues: Water Use, Landfills, and Smog
Will Urban Trees Burden Landfills?
In 1988, EPA estimated that yard debris constitutes 20 percent of the country's
municipal solid waste—about 30 million tons. In recognition of this fact, tree planners
must consider the solid waste implications of planting programs.
Whether or not increasing the number of trees will increase the amount of debris
to be placed in landfills depends, in part, on climate, species, and the street and lot
layout. Resident behavior and the existing solid waste and storm drain systems, however,
also have significant effects on the amount of debris produced and how it is handled.
Fallen leaves are the primary waste of trees. The fate of those leaves depends
on where they land. If leaves fall in a yard or public lot, they can be left on the ground
to decompose, or they can be gathered and composted on-site, in which case they
become a useful soil amendment. If the leaves fall on the street, they may be gathered
by streetsweepers or washed down the storm drain system.
In many communities, leaves also are collected as yard debris. Composting these
leaves produces a useful product, but requires funds for both collection and processing.
If they end up in a landfill, they contribute to an already burdened system, but they
probably do not create harmful leachates.
Other tree wastes include fallen or pruned branches, and dead or diseased trees.
Most residents probably will not compost branches, or leave them on the ground.
More likely, they will be landfilled, burned, or collected as yard debris. Similarly,
removed trees probably will end up in the fireplace, a landfill, or the municipal
compost, if there is one.
A city-wide tree planting program also may have less direct, but equally important
effects on a city's solid waste system. Increased shade, for instance, may alter plant
growth beneath the trees, and create more or less vegetative debris. This is a par-
ticularly important consideration with urban planting programs, because so many
trees will have turf beneath and around them.
Similarly, objects typically exposed to sunlight, including lawn furniture, awnings,
gutters, paint, and shingles, may last longer in the shade, and be thrown out less often.
Finally, some critics worry that street trees will break sidewalks and sewer pipes,
and thereby create more material for landfill. Choosing appropriate species, and
planting carefully, however, should mitigate that problem.
Choosing the
appropriate tree
species for
streets, and
planting them
carefully, can
prevent breaks
in sidewalks and
sewer pipes, and
avoid creating
more material
for landfill.
Trends In Solid Waste
A number of states have banned the deposit of yard debris in landfills. The
alternative is to chip or shred yard debris to facilitate both composting and the use
of wood chips for boiler fuel.
Similarly, by the time young trees that are planted now have significant foliage
and branches, or by the time they become diseased or die, solid waste systems across
the country probably will have changed. Exactly how the systems will change—and
how that will affect content—is only speculative at this point. Hopefully, more
residents will be composting on-site, more cities will have yard debris collection
programs, and more areas will ban the landfilling of that debris. If this happens, more
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yard debris will become compost or broiler fuel, and the percentage ending up in
already overburdened landfills will lessen considerably.
In other words, urban tree planting may very well increase solid waste costs in
cities, but it won't necessarily increase solid waste amounts in our landfills.
Will Urban Trees Worsen Urban Smog?
In the last few years, media attention has focused sporadically on the idea that
trees pollute. This is not a mistaken notion. Studies of individual plants and air quality
measurements show that some kinds of vegetation do emit organic compounds into
the atmosphere. Other studies have shown that biogenic emissions undergo the same
general reactions in the atmosphere as do organic compounds emitted from human
activities (including motor vehicles, solvents, fuel storage and use, landfills and haz-
ardous waste facilities and refineries).
Like anthropogenic, or human-caused emissions, then, these biogenic emissions
can contribute to low-level ozone, better known as photochemical smog.
Compounds Emitted From Vegetation
The chemical compounds emitted by vegetation contain carbon, hydrogen, and,
in some cases, oxygen, and can be classified as follows:
Isoprene
Isoprene (C5Hg) is emitted from such deciduous trees as oak, aspen, sycamore,
and willow, primarily during daylight. Emission rates increase as both light
intensity and temperatures increase. Indeed, one recently published study
indicates that the isoprene emitted from aspen at high temperatures (returned
to the atmosphere) may represent up to 8 percent of the carbon dioxide seques-
tered from the atmosphere by the tree's photosynthesis process.
Monoterpenes
These organic compounds (C1QH16) are emitted from coniferous trees and a wide
variety of other vegetation, including a large number of agricultural crops.
Over 14 individual monoterpenes have been identified as vegetative emissions.
Like isoprene, monoterpene emission rates increase with temperature. The two
compounds emitted from a Monterrey pine tree, for instance, increase by a
factor of 10 when temperatures rise from 24°F to 19°f. Not affected by light
intensity, monoterpenes are emitted 24 hours a day.
Other Biogenic Organic Emissions
In addition to isoprene and the monoterpenes, many other organic compounds
have been identified as vegetation emissions. These include aldehydes and
alcohols containing 1 to 6 carbon atoms; alkanes and alkenes; compounds
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Implementation Issues: Water Use, Landfills, and Smog
related to monoterpenes, including ether, alcohol and carbonyl derivatives
of the monoterpenes; and sesquiterpenes. The atmospheric chemistry of these
diverse compounds is not well understood at the present time.
Biogenic Emissions In Air Quality Degradation
Scientists now know that ozone and other photochemical oxidants are produced
when oxides of nitrogen interact with reactive, non-methane, organic compounds
under the influence of sunlight. Organic compounds emitted from both anthropogenic
and biogenic sources are involved in these photochemical reactions.
Studies suggest, in fact, that the atmospheric lifetimes of biogenic emissions
are at least one order of magnitude shorter than those of anthropogenic emissions,
and that biogenic emissions may be three to five times more reactive than anthro-
pogenic organics in the formation of ozone. The high reactivities counterbalance
the low concentrations, making biogenic emissions important contributors to the for-
mation of ozone and other oxidants in urban and rural areas.
Furthermore, research in Atlanta, GA, has shown that including biogenic emissions
in computer models of urban air pollution can have major implications for control
strategies designed to reduce ozone. Indeed, this same study concluded that controlling
nitrogen oxides may be the most favorable, or perhaps only possible, strategy for
achieving low ozone levels, since reducing the present vegetation is clearly undesirable
for many reasons.
Clearly, the possibility that increased tree plantings could result in increased
emissions of highly reactive biogenic organic compounds must be taken into account.
Of great importance is the finding that the emission rates of biogenic compounds
vary widely from species to species. There is a clear potential to minimize adverse
effects of urban trees by screening candidate tree species for their emissions and choos-
ing, if possible, only those exhibiting low emissions of organic compounds for planting.
Current Uncertainties
Unfortunately, at this time, the biogenic organic compounds emitted from or-
namental trees, and their emission rates, are very poorly known. Indeed, to date, the
emission rate data for biogenic compounds from all types of vegetation are sparse,
and have generally only been obtained from a very limited number of observations.
A long-term experimental program to determine the organic compounds emitted
from the candidate tree species, and their emission rates, over at least one, and preferably
several, growing seasons, should be conducted in each community. This can be done
either through a local university, or, if possible, through a local air quality control board.
Conclusion
Each issue raised in this chapter needs to be researched further, on both a
theoretical and a practical level. Preliminary analysis indicates, however, that the
most obvious problems—water use, waste, and air pollution—can be easily mitigated.
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Indeed, as we examine temperature reduction strategies for our urban areas with
increasing scrutiny, it becomes increasingly clear that one of their primary attractions
is their simplicity.
^^
Further Reading
There are a number of excellent studies of urban vegetation cover, including the
studies by Brown and Winer (1986) of vegetation in Los Angeles, Miller and Winer
(1984) on the same subject, and Rowntree (1984) on eastern cities.
For information on landscape water use, California's Office of Conservation (1986)
has published a number of reports on urban water management and the state's water
future in general. The works by Swearengin (1987) and Nelson (1987) on Xeriscape,
and Meyer and Strohman (1989) on irrigation also are helpful.
For explications of the interactions between plants and climates, see both Oke
(1978) and Jones (1983). The case studies by McPherson et al. (1989) are perhaps
the only quantitative analyses available on the trade-off between energy and water
conservation and are excellent. See also: Southwestern Landscaping That Saves Energy
and Water (The University of Arizona, Extension Publication 8929, 1989) by
McPherson and Sacamano.
Information on native species and other low-water-use species are available from
a number of sources. Books on native plants are usually locally available, as well
as others on drought-tolerant and low-water-use non-native, but tolerant, species.
Excellent examples include Perry (no date available), Coate (1986), and Duffield
and Jones(1981).
There is also software available to help landscapers choose aesthetically appropriate
native and low-water-use species. For example, Acacia Software of Santa Barbara
has produced a plant database with regional modules for California and the south-
western United States. The landscaper can specify any number of plant criteria, in-
cluding water and sun requirements, plant or tree height, canopy shape, blossom color,
maintenance needs, and climate of origin to obtain a list of plants which are site-
appropriate. The program even has a category of plants that are good substitutes for
lawn. See the references section of this book for further sources on choosing plants
and trees.
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Lessons Learned from Successful Tree Programs
E Gregory McPherson
Judith D. Ratliffe
Neil Sampson
Lessons Learned from
Successful Tree Programs
Healthy Trees
49%
Dead Or Dying
2%
Empty Spaces
49%
Today, planting trees to modify the urban environment has become a popular civic
cause. Spurred by the American Forestry Association's (AFA) Global ReLeaf
program, which exhorts citizens to "Plant a tree, cool the globe," and motivated by
local concerns such as potential urban deforestation, citizens across the country are
putting trees in the ground at rates some municipalities have not seen in years.
With all this activity, it is impor-
tant to evaluate the best planting pro-
grams for ideas to improve existing pro-
grams and create successful new ones.
This chapter presents "tales from the
trenches" as told by the planters them-
selves. They are the ones with the real
experience and the ones who provide
the best information and support. This
chapter summarizes a survey of 13 pro-
grams in communities of all sizes and
from all parts of the country. This survey
focused on street programs—because
trees planted in the public right-of-way
are truly community trees—and pro-
grams deemed successful by the AFA
and by other urban forestry experts. In
addition, see Appendix F for ideas on
types of trees and planting locations.
Figure 5-1.
Summary report: Today's
urban forests contain just
as many empty tree
spaces as healthy trees
(AFA National Street Tree
Survey!
Source American Forestry Association, 1990
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The survey also emphasizes programs that have been in existence for some time.
Longevity is a prime indicator of a program's success in gaining sufficient funding
and in sustaining—even heightening—community support and involvement. In all
but two cases, the programs we found have been in existence for at least five years.
Many have been functioning for much longer.
To obtain the necessary information, an extensive questionnaire was sent to contact
people at each program. Those questionnaires formed the basis of telephone interviews
conducted in October, 1989. The questions were open-ended in nature and aimed
at drawing out the kind of in-depth experiential information that short answer surveys
seldom yield.
Readers will find that these 13 programs vary considerably in philosophy, struc-
ture, operating procedures, use of volunteers, and other important aspects. One primary
difference is that some are city government programs and others are private. Such
a mix provides a variety of perspectives on tree planting. The mix also offers insights
as to how public and private programs can work and learn together. In the end, the
shared goals, challenges, and approaches are more important than the differences
between the programs. In addition, some of these other programs in the United States
have been highlighted in boxes to further illustrate particular successes or innovations
in program development and activities.
Surveying The Condition Of The City
The latest survey of city trees and their condition was completed in 1989 through
the National Urban Forest Council, with support from the U.S. Forest Service, the
American Forestry Association, Michigan State University, and a host of state and
city agencies and volunteers. In the first phase, 413 cities were surveyed with a
statistically selected sample set that ranged from five plots in small communities
to 30 in the larger cities.
The data provide information on the amount, size, and condition of the street
trees growing on the "tree lawn" that commonly exists between curb and sidewalk.
Those street trees account for about 10 percent of the total tree population in most
cities. The survey data, expanded to national estimates, suggests that there are about
60 million street trees in the United States today, with an estimated value of some
$30 billion (Kielbaso and Cotrone, 1990).
Of concern, however, is the fact that the data indicate that over half of the
available street tree spaces are empty. Tree planting needs, for street trees alone,
are estimated in the range of 60 to 75 million trees. Developing effective and viable
Large-scale urban tree planting campaigns can be started immediately,
but the practical implications of planning, planting, and care go far beyond the
stroke of policymakers' pens. Simply put, legislation—and even funding—for
tree planting programs will not necessarily result in thriving urban forests.
— Andy and Katie Lipkis, TreePeople (Los Angeles)
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Lessons Learned from Successful Tree Programs
street tree programs could help fill in these gaps. Unfortunately, we don't seem to
be gaining on this challenge in most cities, where fewer trees are often planted than
die or get removed. In the very large cities, this ratio is even worse—as many as four
trees die or are removed for each new one planted in some cities (Moll, 1987).
About Organizational Structure
Paid Staff
Almost every privately funded street-tree planting organization we examined
had a core of paid professional staff. The justification for this is simple. Most
volunteers have other obligations and once a program becomes successful, they can
not keep up with the work. Even the most energetic and clearly focused volunteers
lose steam when they are asked to run an organization for too many months or years.
A paid staff, on the other hand, can develop the high levels of professionalism needed
to avoid squandering a program's potential.
When should the first paid staff-person be hired? Hire as soon as possible. This
establishes the organization as serious and professional from the start, which is
important if you need to usher permits, waivers, and other paperwork through multi-
layered bureaucracies. A paid staff—however small—also conserves the energy of
important board members, who often run the group themselves in the beginning.
Staff size can range from one person to a fleet of knowledgeable professionals.
Trees Atlanta, for instance, a private program operating since 1984, has a paid
executive director, Marcia Bansley, who acts as a general contractor on each planting
project, and a paid part-time volunteer coordinator. Working with volunteer profes-
sional landscape architects and landscape contractors, Bansley investigates the planting
feasibility of selected sites, obtains necessary cooperation from property owners,
and arranges for the city to issue necessary permits, mark utility lines, and make
sidewalk cuts. With the advice of volunteer horticulturists, she also purchases the
trees from an approved species list, puts the project out to bid, and supervises the
actual planting. On the other end of the spectrum, TreePeople, a private program
in Los Angeles, currently boasts a staff of 23 full-time and 10 part-time employees.
In 1986, the organization had only 10 full-time staff members.
When it comes time to expand staffing, the key is to have a complete and detailed
idea about what extra staff will allow the program to do. Then the issue is raising
the money to hire them. Because every program will have its own priorities and or-
ganizational structure, growth direction for programs will differ. Many programs
do quite well for some time with a single paid staff person, usually an executive di-
rector. However, as a program becomes more successful, a single executive director
may become overwhelmed. Because staffing involves money, top-notch business
expertise on the board is vital in weighing the pros and cons of expanded staffing,
and in arriving at a sound business decision.
Sometimes expansion of staff in a particular direction is linked with seizing a special
opportunity. For example, a number of the private programs contacted are going to add
an educational component, or intensify an existing one, by making use of the educational
package developed by Global ReLeaf. In Houston, this chance dovetailed nicely with
Hire paid staff
as soon as
possible to
relieve the
burden on
volunteers and
board members
and to handle
the range of
activities associ-
ated with a
successful,
professional
organization.
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Board and
professional
staff members
work most
effectively when
their areas are
clearly defined.
the desire of several board members to plant trees along the perimeters of school
campuses. This involved obtaining a grant to bring a complete program together, and
hiring someone to administer it. Dona Chambers, the program's executive director,
knew that educational programs can be great for public relations, but she also knew
she had less and less time to devote to that task. A second hire will be someone who
can pull together the educational program, work on public relations, and "earn their
own keep," Chambers said, by raising money to fund the new program.
Advisors And Boards Of Directors
A board of directors comprised of high-profile leaders is also invaluable to a
private planting organization, for it gives the program credibility. Ideally, board
members work, too. But sympathetic community leaders with little time to volunteer
may be used effectively as advisory committee members. They put star power on
the letterhead, but have no time-consuming duties. They also have valuable contacts
and more access to those contacts than a fledgling grassroots group. After such a
committee is formed, a working board is also formed.
The boards of directors of successful groups tend to be, in the words of Peter
Gradjansky, planting program manager for San Francisco's Friends of the Urban Forest,
"supportive and not overly directive." That is, board and professional staff members
work most effectively when their areas of endeavor are clearly defined. For instance,
when board members do foundational work—such as setting policy, making financial
decisions, fundraising, and selecting sites—and staff builds upon it, organizations run
smoothly. But when directors get over-involved in day-to-day operations, say, by calling
staff members directly to give specific orders on pet projects, trouble arises quickly.
It is far more effective to use a paid executive director, who does not sit on the board
but attends board meetings and communicates between the two groups.
Committees are most effective when board members are asked to serve on sub-
committees performing specific tasks. Houston's Trees for Houston program, for
instance, a private program incorporated in 1982, has a 30-member board of directors
which is organized into standing committees responsible for membership, ordinances,
maintenance, long-range planning, fundraising, and other activities. A separate
advisory board lends its members' names to official publications.
Volunteers
Volunteers are all important. Every private program and most of the governmental
programs we surveyed work with volunteers to some extent or another. The difference,
however, is that private organizations tend to depend on volunteers, whereas gov-
ernmental programs work with volunteers mostly on special projects aimed at edu-
cating the public about urban forestry.
Within private organizations, volunteers work at a wide variety of jobs, including
planting, fundraising, office work, and vehicle maintenance. Probably no organization
we contacted had a happier relationship with volunteers than TreePeople in Los
Angeles, where hundreds of volunteers do everything from running the office, to
digging holes, to organizing plantings.
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Lessons Learned from Successful Tree Programs
Again, volunteers cannot replace paid staff. Cor Trowbridge, director of the
TreePeople's Citizen Forester program, says, "As an organization grows, it becomes
more important that certain things be taken care of. Answering the phone has become
one of the most important jobs here. It just can't be volunteer anymore."
A Few Words to the Wise
To avoid turf battles, proceed with initiatives diplomatically. Don't
harangue other departments about what they're doing wrong. Begin small.
Arrange to make species recommendations for an upcoming planting
project. Be ready to back up suggestions with examples of how proper
species selection will save the city money through lowered maintenance
and replacement costs. After a few successes, make it obvious that both
entities will benefit from the relationship. Then move on to larger issues,
such as the development of an approved species list.
Such informal links are truly a challenge in Chicago, with its maze
of interconnected but legally separate taxing bodies (including the city,
the parks district, the water reclamation district, the board of education,
and others), each of which has jurisdiction over planting on lands it ad-
ministers. When Edith Makra was directing Chicago's NeighborWoods
program, she labored, to pull together the splintered responsibility for tree
services in her city. Whenever she planned a planting within a jurisdiction,
she was careful to include Chicago's Bureau of Forestry (legally mandated
to plant and care for only parkway trees) in the process. The bureau had
all the city's urban forestry expertise, but other city entities had no tra-
dition of taking advantage of it and they too often planted poor species
in bad locations, thus squandering their portion of limited municipal plant-
ing funds. In effect, Makra introduced the different players to one another.
Makra's networking activities convinced Mayor Richard Daley to encourage
her to run the new GreenStreets program, where she is charged with fos-
tering inter-agency cooperation.
GreenStreets works to make tree planting, preservation, and main-
tenance a high priority within each jurisdiction, by increasing the Bureau
of Forestry's budget, by securing federal and state grants to plant and
preserve trees, by working with the state legislature to pass legislation
favorable to urban forestry, and by motivating business to have a stake
in reforesting the downtown. In addition, Makra oversees the development
of a city forest master plan.
Private programs also need to learn to coordinate with public agencies
and departments. For instance, in San Francisco, Friends of the Urban
Forest orchestrates the city permitting process, makes arrangements for
site inspection and sidewalk cuts with the city, and contracts to have holes
augured the day before planting. In addition, each property owner who
receives a tree must sign an agreement with the city to care for the tree
and accept liabilities connected with it.
— Andy and Katie Lipkis, TreePeople
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Nothing can
replace the
dedication of
volunteers,
especially in the
early stages of
tree program
development.
Frequent public
recognition of
achievements,
along with
entertaining
and educational
activities, and
contact through
the mail all help
to maintain a
high level of
enthusiasm.
Others agree. Nothing can replace the dedication of early volunteers who do
everything necessary for a fledgling organization. Once a program is up and running,
though, volunteers are best used on special projects, especially plantings. When these
events are approached as celebrations, they can be fun, rewarding, and productive.
San Francisco's Friends of the Urban Forest, for example, provides planters with coffee
and doughnuts in the morning, and a potluck meal at the end of the day.
To keep volunteer enthusiasm high, our contacts suggest frequent public recog-
nition of individual and group achievements, regular scheduling of both fun and
educational activities, and maintaining contact through newsletters and other mailings.
To mobilize for important special events, use an organized method of contact—a
computerized mailing list perhaps, or an established telephone tree.
Trowbridge notes that professional volunteers, including architects, landscape
architects, urban planners, and lawyers, are contributing to TreePeople's success in
increasingly sophisticated ways. He also emphasizes, however, that these busy people
have limited time. Their skills are best suited to special projects with focused goals
and limited duration.
Links To Other Government Programs
Public Programs
Formal links to other departments involved in tree work are invaluable to gov-
ernment urban forest programs. Too often, urban forestry departments are isolated
from parks and recreation, public works, or planning departments. The resulting
communication problems can wreak havoc on the urban forestry department. Horror
stories abound about trees that are poorly selected or poorly placed because other
departments did not confer with the urban forestry experts.
Urban foresters are ultimately charged with maintaining their cities' public trees.
Almost all the foresters we surveyed said they wanted to be more involved in overall
planning and planting processes. Paul Dykema, former urban forester for the City
Forestry Section in Albuquerque, New Mexico, said that it is important for foresters
to get their "fingers into as many pots as possible."
A formally integrated forestry system, however, is not in the foreseeable future
of most cities. Lacking that, our contacts said, informal communications can be most
effective. For instance, in Albuquerque, where the city's tree planting began in the
1950s, tree planting is carried out by the park construction divisions, the public works
department, and private property owners, as mandated by the city's street tree or-
dinance. All of these activities are guided by the design and development division
of the parks and recreation department. The urban forester is charged with maintaining
trees planted by the city. In most cases, street trees planted by citizens are maintained
by the citizens themselves.
One tip: Don't expect volunteers to dig holes. Contract out this back-
breaking labor. It's fine if the holes have to be filled in overnight for liability
reasons. The next morning volunteers will just be removing loosened dirt.
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Lessons Learned from Successful Tree Programs
Ongoing Care
Planning, training, selecting species, and mobilizing labor and resources
to provide ongoing care and management requires considerable forethought
and commitment. Proposed programs must go beyond paying for planting
trees. They also must address the education and training required to prepare
a community for planting, and the resulting forests' long-term care, man-
agement, and survival needs.
The right kind of tree planting program has several key components:
Educate the public to stimulate independent action on private property
and community action on public property. Reaching, informing, and involving
the public is best achieved by working closely with the news media.
Involve local communities in investigating and defining local needs,
problems, and opportunities. Solicit ideas on how trees could help.
Train the community in the technical aspects of species selection,
planting and maintenance and in the social skills of networking and
fundraising.
Plant the first few trees. Is the community ready for the challenge
ahead? How can you lay further groundwork?
Commitment is the key to a healthy urban forest.
Community members need to be dedicated to the ongoing care of those
first trees, and all that follow. The city must demonstrate that it values
the work by doing its share to support the effort.
—Andy and Katie Lipkis, TreePeople
Arrangements between these departments and divisions are coordinated informally.
Despite the absence of mandated procedures for achieving a coordinated effort, and
despite the lack of an approved planting master plan, employees involved in tree
planting feel that great strides are being made towards viewing tree planting and
maintenance as a team effort, and towards understanding the need to view the city
as a whole when making design, planting, and tree care decisions.
Urban planting in Fort Collins, CO, also depends on informal links for integrated
management and consistency. The Forestry Division functions without a community
forest master plan, but has a close working relationship with the planning department.
New trees get planted several ways. Builders are required to plant street trees
as part of the construction permitting process. For each home built, builders also
must contribute to the Park Land Fund, which creates new residential parks throughout
the city. All street development projects undertaken by the Department of Public
Works include street tree plantings paid for as part of the bonding process. The Forestry
Division replaces all large trees that must be removed with one or more small trees.
And to the extent possible, that division identifies unplanted sections in established
areas, and provides street trees and park trees. This system, the city forester feels,
generally results in good species selection and placement.
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Figure 5-2.
Street Construction Dol-
lar: For every dollar spent
on city streets, trees gen-
erally are allotted only
slightly more than two
cents (AFA National
Street Tree Survey)
Funding
Public Programs
Santa Maria Park Superintendent and Urban Forester Bailey Hudson best described
the problem of funding both private and public urban forestry programs when he noted
that as long as they are considered only an "amenity service," funding is not assured.
Cities have many other problems which seem more pressing.
Tim Buchanan, city forester of Fort Collins, Colorado, agreed. "People are used
to the thinking that says, 'We have to take care of our roads,'" he said. "The average
citizen still has a lot to learn about the concept of an urban forest. We have to get
better at demonstrating that we have money needs, and do more documentation and
analysis than other competing departments."
Everybody we surveyed agreed that public education about the benefits of urban
forests is crucial to increasing funding. An informed public will not tolerate an
inadequate city forestry program, while informed funders will give willingly to a
popular cause, both for the publicity and the sense of goodwill.
One tried and true method for increasing trees in the face of low government
budgets is to require tree planting with new construction, roadway improvements,
and other projects. This method gets trees in the ground, but it makes no provisions
for maintenance. Later, as pressures from other departments mount, it becomes easy
for City Council to cut back on crucial maintenance programs. Such moves, of course,
can have drastic effects on tree health and public safety.
Urban foresters claim the best way to avoid this problem is to be able to present
solid cost versus risk analyses for all proposed changes to maintenance schedules.
Successful municipal programs use street tree inventories, including pruning rotations,
to help in discussions about the cost-effectiveness of certain maintenance strategies—
especially at budget-time. For example, being able to prove that a pruning rotation
of five years results in less lower limb damage and falling deadwood, increased health
and longevity for the tree, improved public safety, and reduced replacement costs,
than a ten-year rotation, helps to garner
government financing for the highest
quality maintenance programs.
In order to generate data-rich inven-
tories, a growing municipal program
needs computerized programs, all forest-
ers agreed. The Street Tree Division of the
Department of Parks, Recreation and
Street Trees, in Santa Maria, California,
was one of the first street tree programs
to adopt computerized inventorying. That
inventorying has enabled it to develop a
complete programmed service approach
to maintenance, as well as keep track of
government funds spent on each tree in
the city.
Curb and gutter
$0059
Sanitary sewer
$013
Light/Comm.
$0043
Storm sewer
$0187
Source American Forestry Association. 1990
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Lessons Learned from Successful Tree Programs
SMUD/Sacramento Tree Foundation Shade Tree Program
As a key component of its Conservation Power Program to cool urban heat islands by
shading homes, schools, and places of business, the Sacramento Municipal Utility District
(SMUD) has sponsored over a million dollars annually to the Sacramento Tree Foundation
for tree planting activities. In 1990, a team of SMUD "Energy Advisors" and Tree Foundation
"Community Foresters" conducted energy audits in the SMUD service area to determine the
need for shading. Community Foresters coordinated the location, selection, delivery, planting,
and stewardship of shade trees with citizen volunteers.
The Tree Foundation, a citizen-volunteer planting and stewardship program, met its short-
term goal of 3,000 new tree plantings for homes, businesses, and schools during fall and
winter of 1990. To date, the program also is successfully meeting its 1991 objective of 25,000
trees planted by the end of the year. Over the long term, the Tree Foundation plans to increase
the number of plantings each year to reach its goal of 500,000 new shade trees in Sacramento
by the year 2000.
Specific goals of this program include:
1) Create a citizen tree planting and stewardship program with the ability to meet
the tree demand from up to 40,000 residential, commercial, and school audits
per year.
2) Establish a shade tree inventory and delivery system to meet the planting demands
of the program.
3) Educate and promote awareness among area residents on the energy-saving ben-
efits of planting and caring for shade trees.
Trees For Public Places
Trees For Public Places, a community tree grant program, is designed to plant new shade
trees at parks and schools and along neighborhood streets. The program's record of accom-
plishments includes:
• Funded planting of over 13,000 trees
• Co-sponsored over 345 community tree planting projects
• Sponsored several large oak grove plantings
• Has provided urban forestry training in a 10-week Summer Youth program since 1983
• Receives continuous support of dedicated community groups
Support for the program primarily consists of grants from the County and City of Sac-
ramento, along with an Urban Forestry Grant from the California Department of Forestry.
Fall 1991 activities underway include community groups and neighborhood volunteers
representing nine schools, three parks, and ten residential and business streets who intend
to plant 1,500 trees.
Trees For Public Places provides trees, educational materials, and technical assistance
to each tree planting project. A designated volunteer "Tree Manager," who has been trained
in a tree care and management workshop, follows up on each project for three to five years
to ensure the healthy establishment of new trees.
—Sacramento Tree Foundation, Sacramento, California
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Figure 5-3.
Breakdown of costs in-
volved in city tree plant-
ing programs Generally
speaking, labor costs are
actually greater than
material costs in tree-
planting programs Us-
ing volunteers can re-
duce initial labor costs
(AFA National Street Tree
Survey)
Materials=30%
Mainte lance
Tree Rei
Administration 1 3%
Labor=70%
Source American Forestry Association, 1990
Inventories can be instrumental in
making a case for established pruning ro-
tations—even in times of municipal fi-
nancial woes. As pruning rotations are
lengthened to save money, trees begin
to develop more problems, prompting
hazard and emergency calls from cities.
It is more expensive and less efficient
for emergency crews to answer random
calls over a large territory than it is to
conduct regular maintenance. When a
city's complete tree care activities have
been logged into a computerized inven-
tory, such data is extremely accessible
to urban foresters.
Inventories can also provide the information for analyses of the costs of caring
for one species compared to another, or the varying costs of maintaining a particular
species in different planting sites. This reveals which species are most cost effective
in different urban sites.
Complete inventories, with all maintenance noted in each tree's file, also can
offer proof that a city has not been negligent in its maintenance if it is sued over
a tree care issue.
Forestry divisions that lack the inventory information to generate such figures
and information themselves often can make persuasive arguments based on figures
from comparably sized cities.
Private Programs
There are no easy funding answers for private programs either. Most programs
mix funding from governmental and foundation grants, and corporate and private
donations. Analysis shows that membership strategies take several years to pay for
themselves, because members have to be serviced by newsletters, educational op-
portunities, and other amenities. Still, many groups swore by their members, saying
they were the most loyal givers.
NeighborWoods in Chicago, IL, was very successful in securing corporate un-
derwriting for projects which promised good publicity for both the funder and the
program. Edith Makra credits the nationwide publicity of Global Releaf with attracting
some short-term corporate givers, and she counsels fundraisers to watch for such
tie-ins to larger issues. She also notes that a program needs general operating funds
before it can pull together these high-profile plantings.
Fundraising tends to create its own momentum. The relationship between operating
funds and corporate donations is important. Well-received, special projects create
the kind of publicity that heightens public awareness and educates people about the
urban forest. Increased public awareness, in turn, creates increased opportunities
for general fundraising, as well as new opportunities to put together special events.
72
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Lessons Learned from Successful Tree Programs
The Dallas Parks Foundation
The Dallas Parks Foundation is a non-profit organization that was established in 1982
to privately identify resources and build partnerships to develop new parks and greenspaces,
support existing park systems, encourage public arts uses, and educate the public about
local natural resources. The Parks Foundation has planted more than 18,000 trees in Dal-
las County over the past three years and plans to plant over 38,000 more trees during 1991
and 1992.
Past accomplishments include:
Treescape Dallas, Inc.: An urban treeplanting project of the Dallas Junior League and
the Central Dallas Association from 1982 to the time it merged with the Dallas Parks Foundation
in 1987, Treescape successfully completed 28 landscaping projects in downtown Dallas at
a cost of $890,000. Over 32 percent of this total came from volunteer support and in-kind
donations.
Woodall Rodgers Freeway: By September 1989, 570 trees were planted along the access
road from North Central Expressway to Stemmons Freeway in a joint project with the Texas
Department of Highways and Transportation. The total cost exceeded $200,000 in plant and
irrigation materials.
Cityplace Tree Moving: The Parks Foundation transplanted over 80 trees and shrubs
from the Cityplace construction area to sites throughout Dallas.
Oak Lawn Master Plan: The Parks Foundation facilitated a Master Plan for the major
streets in Dallas' Oak Lawn neighborhood. The work was completed by teams of landscape
architects and other design professionals. Prepared in conjunction with the Oak Lawn Forum,
the Parks Foundation published the plans to encourage consistency in streetscape design
in the Oak Lawn district.
Median Tree Plantings: Planted over 75 trees on major Dallas thoroughfares.
James Surls Sculpture: The creation of the Robert Buford Fund in 1990 allowed the
Parks Foundation to meet its objective of acquiring public art for city parks.
Current programs include:
MKT Trails: The Union-Pacific Railroad plans to donate a 3.7-mile section of the Mis-
souri-Kansas-Texas line to the Parks Foundation. This right-of-way will be developed as a
hike-and-bike trail which will connect a number of neighborhood parks. Completion of design
and commencement of fundraising is anticipated by the end of 1992.
Pioneer Plaza: Under a special agreement with the Dallas City Council, the parks Foundation
will design and build a new park at the Dallas Convention Center adjacent to Pioneer Cemetery,
and will present it as a gift to the people of Dallas. Anticipated construction is June 1993,
completion expected January 1994.
Treeplanting: The Parks Foundation is actively involved in planting trees in parks, along
boulevards, in school yards, and on other public lands throughout Dallas County. With the spon-
sorship of Fina, Trees for Dallas installed over 5,300 trees during the 1990-1991 planting season.
— Dallas Parks Foundation
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A program with a proven track record always has an easier time fundraising
than a new organization. So, it's a good strategy for new programs to seek heightened
visibility through corporate-sponsored special event plantings. The problem is that
many would-be funders, drawn by the chance for publicity, aren't interested in
contributing toward general operating expenses. They want to be assured that all
their money buys trees. In such cases, the program must try to insist on receiv-
ing an absolute minimum for its expenses. For the long haul, a program must have
in place a solid funding base for its core program.
One of the most effective ways to defray costs for private organizations is
also one of the best ways to assure successful plantings. Many of the programs
we surveyed have adjacent property owners pay for the trees, or at least a por-
tion of their costs. Citizens with a monetary investment in trees tend to be more
actively interested in their welfare. In San Francisco, for instance, Friends of the
Urban Forest subsidizes about half the cost of having a single tree planted. In an
ordinary neighborhood, the cost to each participant is $135, part of which is ear-
marked for organizational costs. In low-income neighborhoods, where plantings
are financed through various special grants (frequently governmental), there is
nominal cost to the individual.
Most programs cannot afford to rest on their laurels; they have to get out and
hustle every year for every donation and every corporate grant they get. This is
why fundraising is such an important and time-consuming part of street tree planting.
Indeed, sometimes groups get into financial trouble because they assumed certain
corporate donations were guaranteed for an additional year, and then found out
that the corporation gave the funds to other, seemingly "hotter" causes. In New
York City, for instance, the New York Street Tree Consortium had a financial crisis
when a change in tax laws in 1987 meant that several major corporate funders with-
drew their support.
Fundraising is time consuming, but it works best when requests for support
are linked to specific programs and events. General operating monies (salaries,
rent) are harder to raise and frequently come from the operating allowance the IRS
allows non-profit organizations to keep from membership fees, planting fees and
certain other donations.1 In general, program planning, budgeting, and fundraising
are linked together, looking at least a year ahead.
Most groups constantly search for new ways to raise money, including staging
annual benefits. However, most towns don't need another ball, home tour, or craft
show. Developing unusual, effective fundraising activities is something the emergent
tree-planting movement must address. Perhaps some inter-city networking and brain-
storming between creative volunteers will generate some concepts that will work.
In the meantime, several programs are undertaking major fund drives to establish
legal trusts to generate ongoing funding.
1 The IRS allows organizations to keep 25 percent of donations of this sort for overhead costs. Many
trees organizations keep that percentage closer to 10 percent, to assure people their money really goes
toward planting trees.
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The Twin Cities Tree Trust
The Twin Cities Tree Trust, a private non-profit corporation, was established in 1976 to
employ and train disadvantaged youth to reforest public and low-income properties devastated
by Dutch elm disease. The mission of Tree Trust has expanded to include employment of dis-
advantaged adults and more projects of lasting community value such as tree plantings and
landscape construction. Over 15,000 youth and 3,000 adults in government service and private
employment programs have completed hundreds of landscaping and construction projects
throughout metropolitan St. Paul and Minneapolis, Minnesota. Annually, Tree Trust employs
over 800 disadvantaged youth from five metropolitan counties—in the Summer Youth Employ-
ment Program (SYETP)—and over 900 adults from Hennepin County in Minneapolis—in the
Hennepin County Community Investment Program (HCCIP).
The unique Twin Cities Tree Trust program, blending the employment of disadvantaged
youth with environmental improvement projects, consists of two basic goals:
1) To provide employees with a meaningful and challenging work experience.
2) To provide communities with a low cost quality product.
The state, counties, and municipalities request projects and provide all necessary materials.
Tree Trust designs and implements the projects and supervises the crews. Contributions from
the private sector provide ongoing support services including recruitment, supervisory training,
transportation, equipment, tools, supplies, and administrative support. Funding is received
from both the public and private sectors and from philanthropic support. Tree Trust believes
that this combination of varied funding sources enables the program to succeed in meeting
both goals, an outcome referred to as "Everyone Wins."
SYETP: Tree Trust trains the youth for future employment, stressing a positive work attitude
and basic job skills such as attendance, teamwork, safety, proper use of equipment, working
to exacting standards, and the importance of doing a job well. Because of the wide range in
ability and skill level of the youth workers. Tree Trust encourages individuality and mutual respect.
Individual accomplishments are recognized, including an Award Ceremony and picnic at the
end of the ten-week program. Everyone receives an Environmental Service Citation from their
respective County Commissioner and a Tree Trust T-shirt. The Governor signs a Commendation
for youth who have shown outstanding effort.
HCCIP: Since 1988, Tree Trust has provided employment for economically disadvantaged
and hard-to-employ adults who are receiving general assistance. Basic skills training is modeled
after the youth program because most of the adults who come to the program have not worked
in several years. During the week crews work for an average of twenty hours and attend classroom
training sessions or seek unsubsidized employment during the remainder of the week. This program
rewards good work attitudes and attendance with pay increases. It also allows participants to
stay in the program for a maximum of thirteen weeks until they secure other employment.
Projects include public service and assistance to low-income handicapped residents in
Hennepin County such as mowing and snow removal at no charge to the residents.
Tree Trust maintains a carefully trained staff of forty-five people, including a core staff
of five professionals experienced in directing training and employment programs for disad-
vantaged youth and adults. Summer supervisors are hired on a seasonal basis and trained in
supervisory, construction, landscape, planting, first aid, and other critical skills.
— Twin Cities Tree Trust
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Getting Trees In The Ground: What Works Best?
The most successful plantings with private organizations are those in which citizen
volunteers contribute financially and then take part in the actual plantings. This method
may take more time than either hiring for the job or having mass plantings with
seasoned volunteers. But it works over the long term, because it inspires a personal
investment in the tree. It also helps educate the public. Learning how to plant and
care for a tree is a far more effective educational tool than reading brochures or sitting
through lectures.
This approach isn't practical in all areas, of course. Trees Atlanta's downtown
planting areas, for example, are adjacent to corporate property owners who probably
are not enthusiastic about getting their hands in the dirt. But where using local residents
is practical, it needs to be seriously considered.
Friends of the Urban Forest, for instance, has used Community Block Grants from
the U.S. Department of Housing and Urban Development (HUD) to plant trees in
low-income neighborhoods in San Francisco. Gradjansky has found that the plantings
are unsuccessful when FUF does most of the work, because the residents do not get
interested in the trees. When the planting is done in conjunction with redevelopment
projects—where citizens really want the trees—it works better. The most successful
plantings are ones where the neighborhood takes the initiative from the beginning.
Maintaining The Trees: Can You Afford To Be Unconcerned?
Maintenance is the most ticklish issue in the current street tree and urban forest
planting boom. The trouble is that maintenance seems rather dull and routine. It is
not at all as engaging as the effort to get trees planted. And it is hard to convince
average citizens—who look around and see apparently healthy trees—about the
importance of pruning branches for strength, pruning roots to forestall sidewalk and
curb damage, thinning foliage to allow wind passage, and other necessary tasks.
For reasons of public health and safety, maintenance standards have to be higher
for street trees planted on public property than for those planted on private property.
Both citizens and their government representatives have to understand these issues
and be willing to fund them. As we have seen, however, regular maintenance usually
gets neglected when money runs low.
The most promising plan for lessening the maintenance funding burden seems
to be to have private groups (whether a street tree program or a developer) plant trees,
Urban tree planting is widely recognized today as being one solution
to the global warming problem. But there is a catch to this "solution." The
"technology" is a living one which requires extensive ongoing care if it is
to work. That is, tree planting is not a technical "fix" that will handle a
problem regardless of human action. It mandates an ongoing partnership
between people and their environment.
— Andy and Katie Lipkis, TreePeople
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and then have the city take care of them.
In many cities, adjacent property owners,
who have access to the trees, as well as
program support and training, maintained
the trees during the establishment pe-
riod—which can be up to five years. When
a tree has reached a certain size, and its
care demands expertise and equipment
that most homeowners don't possess, gov-
ernment has agreed to take over the main-
tenance, having saved the cost of planting
and initial care.
Some cities, however, refuse to care
for trees planted by volunteers. San Fran-
cisco, for instance, makes the property
owners, who are permitted to plant trees,
responsible for maintenance. The city
maintains only the right to cite property
owners and to demand tree care if a tree
becomes a nuisance or a liability. In most
cases, this does not deter planting in
neighborhoods committed to having trees.
City foresters, however, do not like
arrangements where citizens are com-
pletely responsible for street tree main-
tenance, because that maintenance is
usually not guided by professional forest-
ers. Too much bad maintenance—includ-
ing inappropriate pruning and tree top-
ping—undermines the appearance and
health of individual trees, and reduces the
value of the urban forest as a whole. Ad-
ditionally, the foresters become like law
enforcers with the unpleasant task of
forcing residents to maintain trees on pub-
lic property.
The Fort Collins program provides a
good example of what can happen when
citizens are held responsible for too much
maintenance. Beginning in 1969, a large
number of that city's trees became in-
fected with Dutch elm disease. The prop-
erty owners—who were primarily respon-
sible for their trees—could not take care
of them. Many of them did not recognize
Excellent
32%
Good
40%
Source American Forestry Association,1 990
Figure 5-4.
Percentage of trees in good condition Almost three quarters of the nation's trees
are in excellent to good condition This record could be continued with proper
maintenance from urban forestry programs (AFA National Street Tree Survey)
Small Trees
3-12'
45%
Medium
12-24'
25%
Source American Forestry Association, 1990
Figure 5-5.
Tree size distribution. Today's urban forest contains many young or small-sized
trees it is important to plant more mature trees and trees that will grow large
enough to provide adequate shading Larger trees tend to be hardier and require
less maintenance (AFA National Street Tree Survey)
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the severity of the problem and simply assumed the trees would regain their vigor.
Others could not afford either remedies or removal. Consequently, property owners
neither treated nor removed their trees quickly enough to prevent contagion. Faced
with the depletion of its urban forest, the Fort Collins government had to step in and-
take over all maintenance.
Of course, waiting for a crisis to develop is not a particularly effective strategy
for forcing a city to sort out its priorities and take charge. Without adequate main-
tenance, our urban forests become run-down, and then move gradually from being
a nuisance to being a threat to safety. Unfortunately, once the public has a negative
association with the urban forest, it is hard to build a more positive image.
In general, the foresters we surveyed agreed that the urban forest receives the
best maintenance and is healthiest when it is managed as a whole, from planting
through removal, by a professional staff. The problem for cities is that the money
is not usually available for the street tree program to go first-class.
ideal Components of an
Urban Forest Management System
City Forester
City or government agency with
planting, management, and mainte-
nance responsibility and funding
Ordinances
Citizen tree commission or board
Citizen and youth involvement
Private contributions
General Public education
Neighborhood-level outreach
Tree Inventory
Tree or Forest Master Plan
Local Government
can be responsible for:
Ordinances
Maintenance
Specifications
Master planning
Tree inventory
Coordination of efforts
Private citizens
can take care of:
Fundraising
Community organizing
Small tree care
Either or Both
can promote:
Youth involvement
Public Education
Training
Planting
Tree Care Activity
Public celebrations
Citizen tree commission
Neighborhood planning
Andy and Katie Lipkis
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Other maintenance strategies developed by private groups include the New
York Street Tree Consortium's citizen pruning corps which consists of over 1500
citizens who are certified by Parks and Recreation. Residents who need help the
city cannot provide can call someone from the Consortium's directory of citizen
pruners. The organization also holds periodic Tree Care Days, on which groups
of pruners gather to tend trees in a particular neighborhood. In Houston, some
citizens commit to caring for the trees with the help of periodic maintenance
workshops provided by Trees for Houston. Some neighborhoods have organized
to do yearly tree assessments and purchase professional maintenance. At the same
time, the program is developing a volunteer maintenance corps. Trees Atlanta includes
three years of professional maintenance in the $2000 per tree charge. After three
years, the city assumes responsibility.
Other cities use a combination of strategies. Friends of the Urban Forest, for
example, has given maintenance workshops with neighborhoods a year after their
plantings. That organization is also forming a corps of citizen pruners similar to
the New York corps. There has been some experimentation with collecting a fee
at planting to contract out for professional maintenance for at least the first year.
The truth is, however, that private planting groups, in general, have inadequate
plans for maintenance. They admit this. If they waited to plant until they had lifetime
maintenance for each tree assured, they say they would never plant. Even in cities
where government crews are slated to take over maintenance after citizens have
planted and established trees, there is concern that the money to actually do this
won't be there as the trees come on line.
In the final analysis, of course, it may be the courts that determine who is ul-
timately responsible for trees planted on public property. Cases that question whether
or not cities can legally assign responsibility and liability to adjacent property owners
are beginning to work their way through the judicial system even now.
About Community Forest Planning
First Steps
Whether you are part of a private or a governmental program, you must first
pick viable species for your area, and then plant them in appropriate sites. All
of the planting programs we looked at have developed approved species lists for
their areas. These lists emphasize natives where possible, but because they must
consider urban growing conditions as well, they often include well-adapted, ro-
bust exotics. Lists usually include species approved for small, medium, and large
planting sites.
Citizens generally want to have some voice in deciding what kind of tree will
be planted in front of their property—even if they don't have to care for it. Most
citizens are quite happy to choose from a short, approved list, and are generally
receptive to tree program advice about design elements. Still, it is important to fully
explain why there is a list of approved species, so residents understand why their
choices are limited.
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Citizen Foresters
One example of citizen involvement is TreePeople's Citizen For-
ester™ Program . We developed it when our grassroots operation began
taking on the dimensions and problems of a centralized organization.
Two things happened. As the demand for tree planting increased,
neither TreePeople's budget nor human resources (staff or volunteers)
could meet the need. Of even greater concern, neighborhoods were
planting trees, but then neglecting them.
As funds were tight, we were no longer able to do fundraising and
get permits, nor were we able to do planning, organizing, or plant-
ing for community groups. Instead, we began to guide them through
the process. And as they struggled to obtain planting permits and money,
they galvanized extraordinary community commitment.
Even in very poor neighborhoods, families began realizing what
they could contribute. On planting day, people would turn out to plant
"their" trees. Even more important, they seriously adopted their role
as tree guardians. One group built its own water wagon, by strapping
two 55-gallon oil drums to a trailer pulled by various neighborhood
cars. In one area, as we helped restake trees after a windstorm, con-
fused neighbors drove by shouting, "Don't hurt our trees!"
The Citizen Forester training currently includes more than 30 hours
of classroom time, plus practical field experience planting and teach-
ing others. Citizen Foresters also learn tree care, fundraising, community
organizing, how to work with government agencies, and more. Partici-
pants actually go through the government permit process and "graduate"
with the planting permit in hand and their project well on the way to
fruition. TreePeople is always there as back-up: It can provide logisti-
cal support, tools, trucks, pooled wholesale purchasing of trees and sup-
plies, and hordes of "roving" volunteers to ensure a planting's success.
Regardless of the form your urban forestry project will take, you
should ascertain whether or not you are duplicating the work of an
existing or planned program. Time and energy have been devoted to
such projects, and lessons may already have been learned. Moreover,
community efforts require, above all else, cooperation, trust, and good
will. Avoid unintentional offence by announcing a project that apparently
ignores what already exists.
— Andy and Katie Lipkis, TreePeople
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Basic components of an urban forestry program;
A truly successful urban forestry program includes a dynamic com-
bination of roles for the community and government agencies. Main-
tenance costs today are far beyond that which most cities can afford;
the cost of public education and training is beyond that which most believe
is necessary. Even with sufficient funds, it's simply no longer possible
to establish trees in most large cities without an extraordinary level of
public involvement.
People who can get involved in tree-planting programs fall into a number
of different categories:
• Individual Citizens
• Youth
• Politicians
• Organizations (churches, clubs, homeowner groups, etc.)
• Government Agencies, including:
-City Forester
-Public Works Department
-Road or Highway Department
-Parks Department
-Fire Department
-Other Forestry agencies (county, state, and federal)
-Environmental Quality Board or Department
-Planning, Building and Safety, Engineering Departments
-Agriculture Commissioner
• Citizen Commissions (Trees, Public Works, Parks)
• Urban Forestry Professionals
-Arborists
-Landscape architects
-Landscape maintenance firms
• Telephone and Electric Utilities (line clearance)
• Businesses
• Environmental organizations
Many or all of these players are already involved with trees in your
community. Historically, they have acted independently, but with the rise
of Urban Forestry as a profession, cities are increasingly making an effort
to coordinate them.
— Andy and Katie Lipkis, TreePeople
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Master Planning
The majority of the programs surveyed do little master planning. Urban foresters
who had good communication with planning and public works departments did not
feel a need for more formal master planning.
Even in these cases, however, an approved master plan would bring increased
consistency and continuity to plantings throughout the city, which would provide
an opportunity for creating some broad planting themes. In cities previously lacking
inter-departmental communication, master planning can initiate contact between
departments by bringing plant experts, planners, and planters together. A master plan
certainly is advantageous in bureaucracies hindered by continual personnel changes.
In the absence of a master plan, a number of cities have established standards
and specifications for tree planting by ordinance (See Chapter 7). This can also give
cities some control over the shape of an emerging urban forest.
Not all master plans are created equal, however. Santa Maria, for instance, ran
into problems when it adopted a master plan that was too specific about street tree
species. Where the city was seeking elegance and uniformity, it ended up with trees
being planted in inappropriate sites. Some trees had to be removed; others just never
thrived. Today, the master plan has been more or less abandoned, and replaced by
a program which matches trees from a selected palette to specific site situations after
it had become obvious how certain sections of town would be developed. Property
owners in the area are given a choice of 10 different trees that will perform within
site constraints and have similar maintenance requirements.
It's important for a private organization to keep in step with a city's street tree
strategy, whatever its state of organization. One good way to initiate cooperation
is to have the city forester, a city planner, or perhaps a council person on the board
of directors for the tree group. This provides an opportunity for developing at least
informal guidelines for street tree planting.
Relationships With City Government
For a private planting organization, the group's relationship to the city, which
usually issues the permits to plant trees on public property, is extremely important.
On a day-to-day level, too, maintaining a good working relationship pays off in the
long run.
The people surveyed indicated that while the mechanics of getting tree plantings
planned and approved by the city may seem labyrinthine at the start, the process quickly
becomes familiar. Planting coordinators usually work with the same city employees
on project after project. It is important that these employees perceive the planting
coordinators and the tree organization as professional and directed, because it makes
them feel they are contributing to a meaningful movement. This will make their input
more timely and professional.
In the highly charged political atmosphere of Chicago city government,
NeighborWoods' Edith Makra learned that nothing elicited cooperation like writing
to the supervisor of someone who has been particularly helpful. Makra was also quite
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politic about inviting bosses to the celebrations of high-profile plantings so they could
receive public acknowledgment. Complaining to authorities about less than cooperative
behavior, however, usually just makes things more difficult.
How Political Do You Have To Be To Survive?
Survey contacts, both in and out of government, felt strongly that street tree plant-
ing and maintenance was a highly political issue because of the funding allocations
necessary for a viable, managed urban forest.
Successful tree politics depends on constantly remembering the importance of
building a broad-based constituency that supports an integrated urban forestry program.
Contacts noted again and again that taking the time to educate the public about street
trees and the urban forest pays. Groups that work hard to attract media attention can
reach numerous and diverse audiences simultaneously.
No matter how popular the program, however, a change from a supportive to non-
supportive city government, whether or not the city funds the program, can mean
progress or closure regardless of the program. "You can always envision upheaval at
the top that could put you back in the Stone Age," said Cor Trowbridge of TreePeople.
Grassroots support from the community ultimately insulates a program from
political tinkering. When the public vocally supports a program, it gets funded. When
the public does not care, the program is propped up by a few people who have vision,
but are constantly seeking funding and friends in high places. The lack of an integrated
and broad-based support network can make a program extremely vulnerable in times
of financial stress or political change.
Contact With The Public
Education
Contact with the public is inevitable because people live in the urban forest and
see the day-to-day operations of street tree programs. Many people, however, can
walk by a tree every day without it being meaningful to them, so most of the surveyed
programs continually seek other opportunities to educate the public about tree and
environmental issues. In other words, once a tree program is established, the next
challenge is mounting a formal education component.
These education programs frequently target grade-school children to instill in
them an environmental awareness. In general, these education projects include both
classroom curriculum and a hands-on planting project at the school to give students
a more lasting connection with trees and the idea of an urban forest. TreePeople has
the largest such program, receiving 30,000 school children a year at its hilltop site,
where some trees are planted and others are distributed to take home. Other successful
educational programs include a city park/arboretum tour offered in Fort Collins and
the use of rope and saddle maintenance crews in Santa Maria. This old-fashioned
method of tree climbing—in which the climber shimmies up the trunk by wrapping
a rope around the trunk and using a small saddle as a brace—draws daily crowds and
provides crews with the chance for some impromptu public consciousness-raising.
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Making literature available to people who seek it can also be a useful part of an
integrated educational outreach program. Seeking exposure at appropriate community
events, such as flower shows or Arbor Day-type celebrations, can be another useful
way to reach large numbers of people.
Promotion
In addition to publicity resulting from day-to-day activities, many programs
specifically plan special events targeted to call attention to their activities. Such events
frequently fall on Arbor Day. Successful ones involve more than ceremonially planting
a tree at an isolated site. High exposure plantings should have a real impact on the
community in the days following Arbor Day, and should involve as many people as
possible. Ft. Collins, Albuquerque, Colorado Springs, and a number of other com-
munities around the country stage mass plantings with the cooperation of citizen
volunteers and city forestry departments.
Both private and governmental programs have good luck with memorial and other
dedicated plantings. One city has a grandparents' grove, where trees are planted for
grandchildren. In all these situations, the individual pays for the planting and a plaque
goes up with the tree or group of trees saying, for instance, "This tree planted in
memory of...," or "These three blocks planted by Twelfth National Bank."
Inspiration
TreePeople is the group that takes a very inspirational approach to the work of
street tree planting. Group leaders talk openly about involvement and empowerment,
about teaching people to use their personal power as a force for positive change. "We've
learned a lot about the power of inspiration," Trowbridge says, "about how far it can
take you, about the power you have alone, but also about personal limitations. I think
we show people what a force for change they can be when they work with other people
and think big."
Deeper Roots Into The Community
Environmental groups around the country have begun reaching out to minority
and working class groups, and street tree planting organizations are no exception.
There's a strong feeling in the cities that a tree-planting program is more successful
when a city's trees are truly for all citizens. There are, however, problems with follow-
up care, especially for the private programs.
San Francisco's Friends of the Urban Forest, as noted earlier, has had less than
sterling success with plantings in low-income areas because the program has had to
take too much of the initiative in getting the trees in the ground. Gradjansky feels
that the key to better success in such neighborhoods is to involve residents more.
This is sometimes easier said than done in areas where trees are not a top priority.
Within Philadelphia Green, which works exclusively with moderate to low income
neighborhoods in its city, no staff consensus has been reached over the organization's
14 years of existence as to whether community involvement is paying off and planting
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trees yields better results. The reality, according to Jonathan Frank, a program
coordinator, is that most of the organization's plantings disappear within a few years.
It would seem that city governments will have to take a leadership role in providing
street tree maintenance in these situations.
Plant the Future, Inc., in Griffin, GA, has reached out to the minority community
in an unusual way. It has entered into a partnership with a local program provid-
ing vocational training to retarded citizens. Tree seedlings, available free from the
state department of forestry, are raised by the training program participants to a size
useful to Plant the Future, which then buys them. The vocational program makes
money. The planting program saves money, and has received positive publicity about
the arrangements.
In Minneapolis/St. Paul, MN, the Twin Cities Tree Trust is based on the 1930s
Civilian Conservation Corps concept and uses trained crews of disadvantaged youths
and adults for municipal planting and construction projects. As in Griffin, this approach
involves minorities in the process without asking them to expend their possibly limited
resources on maintenance in the future.
Landscape Ordinances
All in all, landscape ordinances greatly help the cause of trees in the cities we
surveyed. There were a few complaints about what were viewed as excessively rigid
ordinances forbidding tree planting under various circumstances, especially at city
centers. Generally speaking, however, programs are anxious to work with the city, and
glad to have formal guidelines, rather than bureaucratic whim, shape their relationships.
Marcia Bansley of Trees Atlanta spoke compellingly about the good that had
been accomplished in her area through the passage of landscape ordinances to protect
existing trees and assure replanting when trees are removed. By being identified as
a force in the successful lobbying for such ordinances, Trees Atlanta has received
wonderful publicity in instances where there have been dramatic preservation of huge
old trees. "We've saved more trees through these ordinances than we could ever have
planted," Bansley said.
As already indicated, landscape ordinances requiring tree plantings with new
construction are the basis in many cities of a partnership with developers that helps
the city grow the way residents want it to. These ordinances acknowledge that trees
are as valued as street lights and other infrastructure that are also required. Certainly
from a planning point of view, making way for trees from the beginning makes more
sense than retrofitting a street with trees years later. (See Chapter 7 for more infor-
mation about developing effective ordinances).
Keeping The Program Alive
Many of the contacts surveyed told tales of tree programs that had died. Most
often, the reason was simply, "They just got tired."
How to keep from getting tired? In Los Angeles, TreePeople fights burn-out with
new campaigns. Organizations need to change to reflect the changing needs of the
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Synopsis of Fulton County (Rev. 11/88)
Tree Preservation Ordinance and Administrative Guidelines
ADOPTED: January 30th, 1985 by the Board of Commissioners
INTENT: To provide standards for the preservation and replacement of trees as part of the land
development and building construction process in unincorporated Fulton County. Benefits derived from
the protection and replacement of trees include: 1) Improved control of soil erosion; 2) Moderation
of storm water runoff and improved water quality; 3) Improved air quality; 4) Reduction of noise and
glare; 5) Climate moderation; 6) Improvement of urban wildlife habitat; 7) Increased property value;
and 8) Aesthetics, scenic amenity.
OVERALL OBJECTIVE: To maintain a functional volume of trees to ameliorate stresses associated
with the urbanization process.
ACCOMPLISHMENTS: To date over 60,000 trees will be or already have been planted as a result
of this program, and over 2000 acres of trees have been actively protected—approximately an 11 percent
reforestation of land developed in Fulton County since 1985. On the average, developers have exceeded
our requirements by 50 percent.
Provisions of the Ordinance apply to all activity which requires the issuance of a land disturbance
permit within unincorporated portions of the County. The Ordinance required the creation of admin-
istrative standards for the identification, preservation, and protection of specimen trees and trees outside
the buildable areas of lots (within setbacks), as wel! as landscaping standards for properties with no
trees and situations where tree protection is not feasible.
The Administrative Guidelines were written subsequent to filling the County Arborist position. A
phased in implementation of the tree preservation program began with the approval of the Board of
Commissioners. These guidelines became the substance of the program.
Tree protection during land development is difficult in the Piedmont region due to hilly topography
associated with heavy soils, often resulting in necessary grading through shallow root systems.
Given these complexities of land development juxtaposed with the specific biological needs of trees,
it became evident that an approach towards education and flexibility was necessary in the administration
of the program.
Applicants for land disturbance permits are required to submit tree protection/landscape drawings
as part of the total development package. These drawings indicate limits of site disturbance, tree pro-
tection area, specimen trees, areas of landscaping and revegetation, methods of tree protection, and
utilities, site design factors, and construction activity layout. The guidelines provide general information
to assist the design professional in tree protection plan preparation, Every site is walked by the County
Arborist, project engineers, and landscape architects to discuss planning considerations, and encroach-
ment techniques, in terms of the existing on-site resources. Further support for the tree program is
provided through conditional zoning (landscape strips, buffers, parking islands, etc.).
An innovative approach was taken in the prescription of replacement trees on developing properties. •
To ensure an environmentally functional urban forest for the future, a minimum density of trees is re-
quired per acre developed. This density (based upon tree size), can be satisfied with existing (protected)
trees on the site, replacement trees, or a combination of both. This formula is effective because it
recognizes variability in the extent of land disturbance between types of development projects, and
thus affords the developer some flexibility. The formula does allow clearing where necessary for site
preparation, but also provides a cost savings incentive to keep existing vegetation wherever possible.
Requests for information on this formula have come from jurisdictions nationwide, and from abroad.
—Edward A. Macie, USDA Forest Service
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people who run them, notes founder Andy Lipkis. His program recently switched
from a campaign to plant one million trees for the Olympics to its current campaign
to promote energy-efficient plantings. Other cities are often finding that variety is
the spice of successful programs. In San Francisco, for instance, Friends of the Urban
Forest is planning to become involved in more massive plantings outside the city
to fulfill staff and contributor desires to make a greater environmental impact. In
Atlanta, the fight for and passage of landscape ordinances in the suburbs has heightened
feelings of empowerment and accomplishment. In the Twin Cities, Tree Trust crews
moved from simple maintenance jobs into substantial building projects. In New York,
the Street Tree Consortium will begin offering consulting services.
The programs surveyed have all evolved over the years as they have embraced
new issues and new ways of getting the job done. Allowing a program to evolve while
meeting the needs of the people and the city seems key to running a successful program.
A Checklist To Consider When Initiating Or Evaluating Programs
1. To develop your program's niche, investigate what other planting programs in
your area are and are not doing with tree planting on private and public property.
Begin working where genuine need exists and where there is a legitimate chance
of success. Concentrate on doing one or two things well to start. You can take
on additional campaigns once you are established.
2. Put together a board of directors with an eye toward building coalitions. Here is
a chance to begin forging important partnerships with local businessmen, community
leaders, politicians, planners, forestry, horticultural, and design experts, service
organizations, and individual volunteers. All these sectors should be represented
in planning programs. When it comes to implementation, be specific about the tasks
the board will undertake (fundraising, promotion, education, special events) and
for how long. From the beginning, plan toward hiring at least a paid executive director.
3. Always have a clear picture of how the talents and enthusiasm of volunteers can
best be put to use. At first, volunteers will probably be doing everything. Later,
the most successful tree programs continue to depend on volunteers as cornerstones
of their efforts. These people serve as one-on-one ambassadors of the program
in the community.
4. Pay people to do the routine work. Have volunteers do the inspirational work,
such as planting, educating, organizing neighborhood committees, and special
project planning.
5. The best way to guarantee money for programs is to mix sources. Successful pro-
grams mix funds obtained from memberships, corporate and business donations
and grants, foundation grants, and governmental funds and grants.
6. Successful programs don't necessarily do everything. They provide timely as-
sistance to citizens who have their own motivations for implementing improvement
projects. Experience suggests that the long-term tree planting success is related
to the extent of the involvement of those who directly benefit from the trees.
Develop a planting strategy with this in mind.
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7. To be a success over the long term, programs need plans for monitoring tree health
and providing regular maintenance. A fruitful partnership grows when street trees
are planted and initially monitored and maintained by adjacent property owners.
As trees become more of both an asset and a potential liability, the municipality
assumes more of these duties.
8. Lists of recommended trees for different types of planting sites are extremely
valuable, as are training and literature on the proper way to plant and maintain
young trees. This much planning is absolutely essential.
9. Successful tree planting programs are usually involved in lobbying for the passage
of landscape ordinances in their communities, especially street tree, tree pres-
ervation and new construction planting ordinances. This gives trees legal status.
10. Successful programs are continuously fundraising, educating, promoting, recruiting,
politicking, organizing, and inspiring the public. They are pragmatic, but in-
novative; stable, but dynamic. They evolve with time. Most importantly, they
are visionary.
Some Individual Examples
Throughout this chapter, we have used a number of different tree planting programs
to illustrate successful (and not so successful) strategies. Here are some fuller de-
scriptions of some programs and their histories.
Chicago, IL: Neighborhoods
Population: 8,130,000
Program type: Private, apparently to be absorbed by government.
NeighborWoods was launched in 1987 as an auxiliary program of Open Lands
Project, a non-profit open space preservation group operating in the Chicago met-
ropolitan area. At that time, the city's Bureau of Forestry faced budget cuts that seemed
destined to accelerate tree losses running three to one over replacement.
NeighborWoods focused on working with community groups that wanted to
undertake planting projects. Each group was asked to submit a project proposal.
Community members were required to pick up at least 25 percent of the cost of the
trees and to participate in the actual planting of them. Planting projects included resi-
dential and commercial district street trees, park and school-yard plantings and planting
buffers in railroad right-of-ways. They were targeted to include different socio-eco-
nomic and geographic areas of the city, but they also were chosen to bring visibility
to the program through their impact on the neighborhood. As the program matured
and corporate sponsors became interested in backing high-profile plantings, city gov-
ernment began to take more and more notice, in many cases offering behind-the-scenes
help with projects. Nearly 1,000 trees were planted in a two-year period.
As NeighborWoods developed, it took on a more and more important advocacy
role, working to raise the public's awareness of the need for healthy, well-maintained
plantings in the city. All the while, it continued planting trees, considering this
advocacy by example and hands-on education. The organization was increasingly
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able to lend important support to attempts by the Bureau of Forestry to stabilize its
budget and improve its service, many times by mobilizing community groups to attend
budget hearings.
The organization was funded by a combination of government and private foun-
dation grants and corporate donations. Fundraising was handled by Open Lands.
When Richard Daley became mayor, he lured NeighborWoods' creator and its
single staff person, Edith Makra, to his office to run the new GreenStreets program.
As of this writing, it remains to be seen what role NeighborWoods will fashion for
itself, with GreenStreets committed to planting 450,000 trees, saving 50,000 trees
in imminent danger of destruction, and providing funding to upgrade maintenance
of trees. NeighborWoods has not hired a replacement for Makra, but has indicated
a commitment to continue community education through planting trees.
Colorado Springs, CO
Population: 393,000
Program type: Governmental Forestry Program, within Natural Resources Division,
of the Parks and Recreation Department
Colorado Springs' commitment to urban forestry was codified into ordinance as
early as 1910, and older parts of town are forested with large, old trees. An ordinance
specifically mandating that developers plant street trees during new construction,
with the city picking up a portion of the cost, has been on the books since 1976.
As it developed, the New Homes Tree Fund, created by the ordinance, has become
a boon to the city. In the early years of its existence, the fund—a repository for de-
veloper portions of new home tree fees—was allowed to build up without being spent
because builders preferred to plant their own trees, rather than involving the city.
By the time the city disallowed this practice, enough money was on deposit that today
the fund generates sufficient interest to cover the city's portion of all new home tree
planting costs.
Colorado Springs also has a variety of other planting programs. In 1977, the city
forester initiated a program called Decade of Trees conceived to help reforest parts
of town where losses to Dutch elm disease were heavy. Today, this program is used
wherever fill-in street tree planting is requested by citizens whether a removal has
taken place recently or not. The city pays up to $50 for trees planted under this program,
with adjacent property owners also contributing. The city's portion of this program
comes from funds generated by the Damaged Tree Fund, the repository for assessments
and fines leveled against people who have damaged city trees.
The city finances an arterial street tree planting program and a park planting
program, always emphasizing the right tree in the right place. It also automatically
replaces any trees it removes of 8-inch caliper or more where room allows. The city
requires adjacent property owners to fertilize and water street trees. City crews provide
disease control, pruning, and removal until trees reach an 8-inch caliper. Care for
large trees is contracted out at a cost of approximately $200,000 per year.
The city's inventory of over 70,000 street trees is computerized, with scheduled
maintenance at least every eight years. Maintenance is also provided upon request.
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A community forest master plan is in the works and is considered a major priority.
The Forestry Program has 13 full-time employees. Its work is funded through the
city's general fund.
Several private groups interested in civic beautification and tree planting are
expected to have a significant impact on tree planting in the city. One, Trees for the
Future, aims to become a funding source for both city and privately sponsored tree
planting projects. Another, Greensprings, plans a major volunteer planting project
once a year with the help of the Forestry Division. Hundreds of volunteers are involved
in the projects, which have included placing seedlings at freeway interchanges.
Los Angeles, CA: TreePeopIe
Population: 13,770,000
Program Type: Private
TreePeopIe began in 1973, when founder Andy Lipkis began to dream of saving
the smog-damaged San Bernadino National Forest. His idea was to plant millions
of smog tolerant seedlings in the mountains surrounding the Los Angeles metropolitan
area. Today, the organization's primary concern is for the urban forest in the Los
Angeles Basin. But the organization is planting fewer trees itself, and diverting more
energy toward training what it calls "Citizen Foresters," who are community organizing
specialists capable of organizing whatever sort of planting program (or presumably
any other sort of program) a neighborhood wants.
The current goal is to create a body of 500 to 1000 Citizen Foresters and to provide
them with a variety of expert support services. Because of its longevity, the organization
has a stable corps of trained volunteers that it can mobilize for worthwhile projects.
Historically, a great many of the Citizen Foresters and neighborhood groups that have
taken on projects through TreePeopIe have been interested in planting street trees
because the permitting procedure is quite straight forward and planting is done ac-
cording to the city's street tree master plan. The organization asks trained Citizen
Foresters to take on at least one new project per year. To date, it has had mixed results
with people keeping to this commitment.
"We've learned you don't have to plant every tree yourself," says Cor Trowbridge,
director of the Citizen Forester program. "We're really becoming known as envi-
ronmental problem solvers. We want to offer tools and expertise and show people
their personal power as a force for positive change."
The organization, which currently boasts a staff of 23 full-time and 10 part-time
employees, is divided into many different units and is administering a broad range
of programs. It recently entered into an agreement with the city of Los Angeles to
direct a campaign highlighting energy savings through the planting of shade trees.
Its first shared project with the city was to help develop a city-wide recycling program.
TreePeopIe's continued role in the recycling program has been incorporated into its
educational endeavors. Every year, 60,000 grade school children visit the TreePeopIe
site (a retired 1920s mountain fire station on 12 acres of wooded land along a mountain
ridge in Beverly Hills, donated by the city, and dubbed Coldwater Canyon Park) for
a tour and lessons about trees and recycling. Each child plants a seedling while there
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and is given a seedling (grown by the TreePeople nursery program) to take home.
The purpose is to inspire environmental leadership in young people.
TreePeople's move away from staff-initiated planting projects and toward com-
munity group projects was based primarily on concerns over maintenance. The group's
well-published campaign to plant one million trees in L.A. for the 1984 Olympic Games
ended in fairly heavy losses in some areas because there was not enough follow-up
maintenance. Although public support engendered in part by TreePeople's activities
seems to be helping the funding situation for the L.A. Division of Street Trees, trees
are visited only about once every six years. Without neighborhood groups committed
to caring for trees during establishment years, TreePeople found many tree plantings
were unsuccessful.
TreePeople is funded through its memberships (7,000 members), individual and
corporate donations, foundation grants and a major grant, now in its second year,
from the City of Los Angeles. The grant from the city has spurred a considerable
staff expansion. TreePeople charges for its Citizen Forester training programs and
for other training programs, such as the one to educate plant supervisors, who will
be able to assist homeowners in the plantings for energy conservation, among other
things. There is a $90 charge per tree to property owners for all neighborhood plantings.
The organization's board of directors makes important financial decisions and
acts essentially in the capacity of a steering committee, as it makes decisions about
what sorts of outside groups and activities TreePeople will get involved with. Because
the TreePeople concept has been exported as far away as Australia as a model for
environmental action through planting trees, the organization is increasingly ap-
proached to enter into partnerships for action of one kind or another.
Philadelphia, PA: Philadelphia Green
Population: 5,963,000
Program Type: Private
Philadelphia Green was established in 1976, as a special undertaking of the
Horticultural Society to provide education and practical development in moderate-
to low-income communities within the city. The intention is that community orga-
nization point the way toward stabilizing and revitalizing neighborhoods that are
frequently in blighted areas. The organization emphasizes both street tree plantings
and "lot-scapes," or gardens created where buildings have been razed, frequently as
a consequence of fire. There are some 17,000 vacant lots in the city.
The organization is well-established and frequently publicized, and has no lack
of requests for help. Typically, once Philadelphia Green begins working with a neigh-
borhood, the process is to identify important community leaders and create a program
plan in accordance with what the community seems to want and need. Lot-scapes
can be strictly ornamental or they can include vegetable gardening and play areas.
Philadelphia Green (financed by the Horticultural Society, foundation grants and cor-
porate funders) pays for plantings. It has fluctuated back and forth over the years
between requesting that community volunteers help plant projects and simply requiring
that communities attend an educational workshop before qualifying for a planting.
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There is still no staff consensus as to which is most appropriate, considering the lack
of resources apparent in many project communities.
The tree planting arm of the program will expand in the near future, under the
auspices of a local foundation, as the organization joins forces with the city to co-
ordinate the planting of 4,000 trees in four years in neighborhoods where redevelopment
projects have been completed.
The city's parks department, called Fairmont Park, after the city's largest park,
usually regulates the tree planting activities of Philadelphia Green. The department,
to the extent of its limited budget, plants street trees throughout the city and does
what it can to maintain them. Philadelphia Green, for its part, tries to maintain trees
during establishment years with a summer program of inner city youth trained as prun-
ers. Then, it educates communities through workshops and printed material about
the need to care for trees in the absence of regular city maintenance.
"The life expectancy of street trees in this sort of urban setting is seven to ten
years," said Jonathan Frank. "It may be that maintenance over the long term is not
the issue we tend to think it is. These may become disposable trees."
The organization includes a paid staff of 35. Hundreds of volunteers have been
involved over the years in planting and caring for trees and gardens. The staff mounts
a Junior Flower Show program in schools throughout the city each year. It also or-
ganizes a Harvest Show each fall to show off produce and flowers grown in its own
community gardens.
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Susan Davis
Phil Martien
Neil Sampson
Planting and Light-Colored Surfacing
for Energy Conservation
People have been using trees and light-colored surfaces to cool their houses and
communities for hundreds of years. That doesn't mean we all know how to do it,
however. In the industrialized world, especially, we have come to rely more and more
on mechanical cooling systems—including fans and air-conditioners—to counter high
temperatures. Traditional methods have been forgotten, and others simply are not applied.
This chapter is designed as an introductory guide to the basic steps of planning
strategies for landscaping and light-colored surfacing for homes, neighborhoods, or
communities. It includes discussions of both street trees for communities and neigh-
borhoods, and single trees for residences. Again, the dearth of practical experience
with light-colored surfacing strategies means that the emphasis in this chapter is, by
necessity, on trees.
Figure 6-1.
City streets: Planting
more trees on the streets
could supplement our
mechanical cooling sys-
tems.
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Landscaping For Energy Conservation
With proper planning and knowledge, planting trees to reduce energy needs can
be a fairly smooth operation. But the emphasis needs to be on "planning" and "knowl-
edge." Creating an efficient urban forest takes more than digging holes in the ground
and plopping in young trees. Trees are living things. As such, proper planting requires
detailed species selection, careful site selection and preparation, and continuous
maintenance. Each of these, in turn, requires time, effort, attention, and, of course,
funding.
This is especially true for trees in the city. Trees in the wilderness grow fairly
easily, impeded mostly by disease, pests, and dramatic climatic events. Urban trees,
by contrast, suffer from a number of human-caused stresses. Air pollution, water pol-
lution, soil compaction, and space confinement all make it difficult for a city tree
to grow as well or as long as its country cousin.
Regardless of
species, size, or
age, all trees
depend on soil,
water, and space
for survival.
Proper planting
requires detailed
species selec-
tion, careful site
selection and
preparation, and
continuous
maintenance.
Figure 6-2.
Sample guidelines for
planning tree planting.
The American Forestry
Association proposes
new tree planting tech-
niques that allow roots
to expand beneath pave-
ment and water to drain
properly.
What Trees Need
Regardless of species, size, or age, all trees depend on certain elements for survival.
They need soil for mechanical support, nutrients, and moisture. They need the heat and
light provided by sunlight. They need sufficient amounts of air, which supplies oxygen
and carbon dioxide. They need space above-ground, so their trunks and crowns can grow.
And they need space below-ground, so their roots can grow to find air and water.
Gravel under pavement improves
air and water movement.
Surface mulch or pavers
set in sand -
no tree grates!
Compacted rootball
support pad.
Trunk-wrap species
with thin bark.
Stake and guy only
trees in very windy
locations.
Remove wires after
4-6 months.
Set rootball higher than
adjacent pavement.
Where possible, extend
rooting space under
pavement.
Drainage and inspection tube.
Source Moll and Ebenreck, 1989
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These needs seem basic. But in an urban environment, each can come in short
or faulty supply. Soil is often compacted, contaminated, or has poor drainage. Sunlight
can be blocked by tall buildings. Air supplies can be so polluted that the trees, while
they do us the favor of absorbing paniculate matter, begin to wither and die. Above-
ground space can be reduced by buildings and utility lines, and below-ground space
can be reduced by underground wires, building foundations, compacted soil, and
retaining walls. In addition, damage caused by vandalism or accidents can hurt a
trees' chances for survival.
Cities are cities regardless of our good intentions. It is impossible to mitigate
these basic urban conditions. But with proper species selections, and with proper
site selection and preparation, you can make a match that is more viable than planting
a fragile tropical tree in Chicago's busiest downtown intersection, and then hoping
it will survive unattended.
In addition to design considerations (including crown shape, blossom and foliage
color, scent, and cluster density), we need to consider soil conditions, water quality,
and space availability during plans for planting. Throughout the process, we must
also consider the needs of the ultimate mature tree, rather than those of a seedling
or sapling. A mature tree has different needs than its youthful predecessor.
Soils
Soils need to be clean from toxic
substances, and fairly uncompacted. In
many instances, you may have to mix in
soil that is looser than what exists on site.
The ideal soil is deep enough and drains
well enough to prevent rapid changes in
temperature, oxygen, and water content.
It is also stable enough to support your
tree. In addition, it may help to erect bar-
riers around the tree to prevent pedestri-
ans from walking or sitting on the soil.
Any barrier, however, must be placed so
that it damages neither the roots nor the
trunk of the tree.
Water
Water needs are a serious consider-
ation in any tree-planting program. Many
cities have serious water shortages for
much of the year. Most cities have prob-
lems with drought in a tree's microcli-
mate, for compacted soil, sidewalk, and
pavements all resist water absorption,
thereby depriving a trees' roots of much-
source Adapted from Southern
California Edison Company, 1990
Figure 6-3.
Avoid planting trees right
next to drainage pipes.
Figure 6-4.
Trees need to be placed a
good distance away from
concrete sidewalks
Source Adapted from Southern
California Edison Company, 1990
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too little
space for
roots
Source Moll and Ebenreck, 1989
Figure 6-5.
Improper tree planting. The planting procedure used in most cities today entombs
tree roots and contributes to the tree's early death
200
150-
50-
Downtown
City Average
Best City Site
Rural Site
Source American Forestry Association, 1989
Figure 6-6.
Comparison of tree longevity relative to location. In general, urban trees have not
lived as long nor grown as tall as their rural cousins Careful planting and
maintenance, however, can help our urban trees flourish
needed moisture. Using loose soils, in-
stead of compacted ones, and using brick,
instead of cement, can help alleviate this
problem. So too can using any one of a
number of "injector" irrigation technolo-
gies, which get the water right down into
the roots of a tree. (See Chapter 4 for a
more thorough discussion of balancing
water needs with energy conservation.)
Space
Space considerations reign pre-emi-
nent among the obstacles faced by urban
foresters. Trees have to compete with
buildings and utilities above ground, and
with utility lines, building foundations,
and sidewalks below-ground. Planting
trees with the proper crown shape can help
with above-ground concerns. Planting
trees in containers can help with below-
ground difficulties, but trees can become
root-bound that way, and in colder cli-
mates, they lose the thermal heat of the
earth. This can be crucial to their survival
in winter months. Again, it is best to
confer with a horticulturist on these
matters. He or she will know what is best
for your city trees in general, and for
selected sites in particular.
General Planting Guidelines
Finding A Site
Generally speaking, three kinds of
trees are available for planting: rural trees,
street/park trees, and shade trees. Rural
trees sequester carbon dioxide, a green-
house gas said to contribute to ozone
depletion. Street and park trees help cool
communities through evapotranspiration.
Shade trees, in addition to evapotranspi-
ration, can reduce air-conditioning needs
for an individual building by shading
roofs, walls, windows, and air condition-
ers. Both shade trees and street/park trees
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also help reduce the amount of carbon di-
oxide in the atmosphere by lowering elec-
tricity demand.
The following guidelines were com-
piled from work by John Parker of Florida
International University, E. Gregory
McPherson of the U.S. Forest Service,
Gordon Heisler of the U.S. Forest Service,
and researchers at Lawrence Berkeley Labo-
ratory. These can be included in city ordi-
nances, or distributed as public information.
Shading The Air Conditioner
1) Air conditioning is the primary com-
ponent of electrical peak demand. The
single most cost-effective way to re-
duce your cooling needs is to shade the
building's air conditioner and the
immediate area around it. Air condi-
tioners become less efficient as tem-
peratures get higher. Preliminary mea-
surements show that planting trees or
erecting a trellis covered with vines
around an air conditioner can reduce
air temperatures around it by 6 or 7°F.
This can increase the efficiency of the
air conditioner by about 10 percent
during peak periods (Parker, 1983).
2) To cool your air conditioner, plant
several trees, so that after a five-
year growth their canopies will com-
pletely shade the air conditioner and
the adjacent area during mornings
and afternoons throughout the entire
cooling season.
Shading The Building And The
Adjacent Ground
1) Because heat transfer through walls
(particularly concrete and brick walls)
causes a delayed impact on air condi-
tioners, plant trees so they will shade
the east- and south-facing walls to reduce
peak period consumption. Plant other
Source Missouri Natural Resources Department {Koon, 1989)
Figure 6-7.
Shading the air conditioner with a vine-covered trellis or trees
can provide enough shade to make a noticeable difference in
temperature.
Source Adapted from Moffat and Schiler, 1989
Figure 6-8.
Vines provide shade and evapotranspiration benefits Use
them while young trees and shrubs mature.
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A few tips on space:
1) Increasing the size of the initial hole dug for a tree benefits its health
throughout its entire lifetime. No studies have determined the ideal
size. But a number of studies have shown that holes of less than
100 cubic feet cannot sustain long-term growth for mature trees 10-
15 feet tall.
2) In general, the branches of trees need to be ten feet higher than side-
walks and fourteen feet higher than streets to maintain space for
passersby.
3) Studies have shown that trees planted in open lawn areas which are
near to paved areas, rather than in them, fare better than trees planted
in constrained tree pits.
4) Similarly, trees protected by tree grates and tree guards tend to be
less healthy than those standing free. Not using these protectors saves
considerable amounts of money—and the lives of a considerable num-
ber of trees.
trees along the west wall to reduce air-conditioning needs during the late afternoon
and evening after the period of electrical peak load. Air-conditioning energy use
can be reduced 40 or 50 percent, or even more, by shading windows and walls.
2) The ideal pattern for shading walls is to plant trees so that, near maturity, the limbs
reach within five feet of west or east walls and overhangs, and three feet of south
walls or overhangs. Carefully placed trees provide optimal shading patterns and
create cool microclimates directly adjacent to the house. Beware of planting trees
too close to the building. Roots can damage the foundation, and large limbs can
cause severe damage if they fall.
3) Similarly, place tall shrubs within four feet of west, east, and south walls, so
that the inside edge of the hedge will reach within one foot of the walls within
four years. While your trees and shrubs are still young, consider planting vines
along the walls for direct shading. While less effective than trees or shrubs, they
are a worthwhile substitute while those are coming of age.
4) To further optimize cooling, plant an understory of shrubs and groundcovers,
especially if the trees are already surrounded by concrete and asphalt. Similarly,
planting trees in clusters helps them keep each other cool.
5) If you have a solar collector on your house, try not to shade it during the day,
even by deciduous trees.
Influencing Wind Movement
You also can plant trees to influence wind movement around and through a residence.
The idea here isn't so much to reduce winds, as they can help cool your home, as to influence
the wind's circulation patterns.
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Air
Conditioner
Source Parker, 1982
Winter
Winds
Coniferous
windbreaks protect
house from cold
winter winds. Trees close
to house on
east and west protect
against summer sun.
Trees on south side should
be deciduous to permit
winter sun while shielding
the summer sun.
TTI
Summer
Winds
Avoid dense trees in the
direction of summer
winds that block
desired cooling breezes.
Figure 6-9.
Sample residential land-
scape: Large trees are
planted on the west and
south sides to cast the
maximum shadows and
on theeastside toshade
the air conditioner.
Shrubs planted on all
sides of the house help
to reduce wall and so/I
temperatures.
Figure 6-10.
Strategic planting dia-
gram: Trees in temper-
ate climates must be
chosen and planted to
shield a house from
both the hot summer
sun and the cold winter
winds.
Source Huang, 1990
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Plastic overlays
for the diagrams are
available to indicate
amounts of radia-
tion from the sun
at different points
in the sky for clear
days. Data from the
diagrams can also
be used to find the
length and direction
of tree shadows on
the ground.
Scale models of
buildings and trees
with a small sun-
dial and a map to
represent the sun
also can be useful
in shade planning.
—Gordon Heisler
Planning Shade
A simple tool for shade planning that arborists might use is the "solar path diagram."
These are available for each four degrees of latitude. The diagrams provide a general sense
of how to manage trees for shading and the times when a tree will shade a particular point
of a house.
Shade on win-
dows is especially
important. Deter-
mining how a win-
dow is shaded by
an existing tree
throughout the year
can be done by
standing at a point
near the middle of
the window and
sketching in the tree
outline on a copy
of the solar diagram.
Angles can be esti-
mated or measured
with a compass and
clinometer.
SUMMER
Dusk
WINTER
South
Horizon Line
\J Dusk
West
Source Missouri Natural Resources Department (Koon, 1989}
Figure 6-11.
Solar path diagram: Shade diagrams such as this one can help homeowners plan the
optimal energy-saving landscape.
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1)
2)
Adapted from Moffat arid Schiler, 1981
If you use minimal air conditioning in your home, you can position trees and shrubs
so they funnel breezes into the windows, thereby maximizing natural cooling. First,
determine the prevailing wind directions. Then prune back the low branches of sur-
rounding trees to allow prevailing summer breezes to pass through the house.
If you use a lot of air conditioning, however, creating winds with tree position
can actually increase air conditioning use, because warm breezes increase warm
air infiltration and heat the interior. (This is generally only a problem in the South-
west). You can avoid this by placing shrubs and trees so winds are channelled
into the dwelling when the windows are open, but away from it when the windows
are closed.
In south Florida, for example, where Parker conducted his study, the prevailing
summer winds are from the southeast. Consequently, air infiltration through the
windows can be reduced by locating tall shrubs close to and on the north sides of
east-facing windows and the west sides of south-facing windows. When the windows
are opened during mild periods, these same shrubs will facilitate natural ventilation
through the windows.
Figure 6-12.
Trees channel breezes
Homeowners with a
good deal of land can
plant trees so they will
channel naturally cooling
breezes
Choosing Species
The species you choose have to be appropriate both for the general climate of
the city and for the microclimate of the exact site you select. Both of these factors
are far too variable for this guidebook to tell you exactly which species to choose.
A number of groups and software programs exist to help you match your criterion
with what is available. Your local nursery, extension service, or university forestry
department also can help you decide which species are most appropriate for your needs.
The following, however, can give you a rough idea of what criterion to consider.
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1) Hardiness: Be sure to choose a plant that can survive the extremes of hot and
cold in your city. The U.S. Department of Agriculture has a number of maps which
delineate plant hardiness zones for the entire country. Be sure also to choose
trees which resist disease and insect pests and which are fairly drought-tolerant.
2) Tree shape has a direct bearing on how well a tree grows in a selected site. Oval
or columnar trees fit well in narrow spaces, often close to buildings, because
they generally grow upward, rather than outward. They are not, however, a good
choice for spaces near utility lines. Round trees with descending branches demand
considerable amounts of space, but are beautiful to look at and play in. Round
trees with ascending or lateral branches work well in spaces where trucks, pe-
destrians, and other traffic needs to pass beneath the tree. Vase-shaped trees,
like elm and zelkova, are particularly well-suited to city streets because they
grow up and out, while forming a shady canopy over streets, walls, and sidewalks.
3) Tree shape also directly affects how well a tree will shade a building. Generally,
a canopy that is moderately thick is ideal. A very thick canopy blocks sunshine
effectively, but it may make the interior of your building too dark.
4) If you are planting trees on the east and west sides of the building, plant trees
that will grow tall if you are planting at a distance, as they will create a nice
long shade in the early morning and late afternoon. If you are planting up close
to the building, plant broad-canopied trees.
The species you
choose have to
be appropriate
both for the
general climate
of the city and
for the microcli-
mate of the exact
site you select.
Figure 6-13.
Plant lines and plant
forms: This figure illus-
trates vertical, weeping,
and horizontal plant lines
(above); and pyramidal,
spherical, vertical ellipse,
and horizontal ellipse plant
forms (below). It is help-
ful to consider the lines
and forms of trees in land-
scape design. Some
plants may change as
they mature Crowns may
spread or open, and limbs
may be lost
Source McPherson and Sacamano, 1989
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5) If you are planting along the northwest or northeast corners of the buildings, also
use tall-growing species. In the late afternoon and morning, these trees will cast
a long shadow along the north face of the building, thereby helping to cool it.
6) For trees on the south, southeast, and southwest corners of the building, plant
deciduous species trees. In the winter season, these species will allow more sunlight
to reach windows and walls than will evergreens. Be sure not to create a shade
across south-facing windows as well, as this will block desired sunlight. In some
northern areas, you may want to avoid planting trees on the south side altogether.
That way, you will have access to as much winter sunlight as possible.
7) If you are planting in a parking lot, broad canopies are most effective as their
shade covers the larger areas. It is also important to choose species with leaves,
berries and blossoms that do not drip and stain. When you are planning the planting
design, try to create islands of trees, rather than planting individual trees across
the area. Trees clumped together share soil, help keep each other cool, and create
a broader shade shape than do isolated trees. Such islands need to be curbed to
protect the trees from bumper damage, soil compaction, and oil runoff.
8) Try to find out how much maintenance different trees require. The American
Forestry Association has estimated that, on average, maintenance takes 40 percent
of a tree program budget, 80 percent of which goes for trimming. Choosing trees
that are vulnerable to disease and pests, or that require frequent pruning, can make
your maintenance costs soar needlessly. Again, your local nursery or horticulturist
can help you with this.
Tree on west
12pm
2pm
January July
Tree on south
Sam
10am
12pm
January July
Taller, pruned tree on south
8am
10am
12pm
January July
Figure 6-14.
These figures give a
rough estimate of the
ways in which shade pat-
terns change on both a
daily and seasonal basis.
Be sure to correlate these
with local conditions.
Source Heisler, 1989
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It's important to
encourage
community
leaders and
developers to
save existing
trees and in-
clude landscap-
ing in any
development
plan.
Cooling A Neighborhood Or City
To help lower an entire city's temperatures through evapotranspiration, you need
to plant as many street trees as possible in public as well as private spaces. Parking
lots, plazas, street meridians, sidewalks, residential yards, corporate lawns, parks,
shopping plazas, and many other niches are currently full of empty tree spaces.
New developments—which spring up constantly in many communities—are an
excellent place to begin planting for heat-island reduction. Too often, however, these
developments are just bulldozed in as quickly as possible, rather than being envi-
ronmentally landscaped. Existing trees often are plowed under in this process, leaving
a landscape bereft of their cooling and aesthetic benefits.
The difference between the two approaches reflects the attitude of city leaders,
planners, and citizens toward the relationship between cities and nature. It's important
to encourage leaders and developers to keep existing trees in developments, to plant
replacement trees whenever the existing ones are destroyed, and to include landscaping
as part of any development plan.
Unfortunately, many of our older cities were built with the latter attitude. But
if new communities and developments learn from the mistakes of older cities, we
can utilize the opportunities of the natural environment right from the outset. The
result will be a better urban environment, at a lower long-term cost to the citizenry.
The best time to make a city fit into the natural environment, of course, is during
the planning and development phase. For instance, new subdivisions in treeless areas
can be required to plant large-growing trees as part of their development plan. Even
very large trees can be transplanted into new urban development sites through skillful
planning and execution. Proper placement of trees in new construction is as logical
a part of development as locating streets and sewers and isn't overly expensive. In
Milwaukee, WI, studies have shown that trees cost only about 2.2 cents of each con-
struction dollar.
Obviously, that time is long past in many urban places. The best strategy, then,
is to improve planting and management programs so as to mimic the natural world
as closely as possible.
Significantly improving the ecology of the urban community calls for large trees,
not small ones. The cooling of the urban heat island, the reduction of air and water pol-
lution, the provision of wildlife habitat, and the visual impact breaking up the urban
scene requires trees that can grow large and live long lifetimes. Rather than designing
trees to fit inadequate urban spaces, we must design urban spaces to fit trees.
The single most
effective way to
reduce your
cooling needs is
to shade the
building's air
conditioner.
Parking Lot Tips
Parking lots can be shaded with little or no reduction in parking capacity.
Extra planning to coordinate tree locations with lighting facilities, however,
is needed. Adequate night-time lighting can be provided with 14-16 foot
high light poles that are located at least 16-18 feet from trees. Tree planting
space at least 5 feet wide can be borrowed from paved areas between rows
of cars by allowing car bumpers to overhang planter space.
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Source Adapted from Parker. 1982
Figure 6-15.
(above) Parking lots without vegetation for shading are
extremely vulnerable to the penetrating solar heat.
Figure 6-16.
(Below) Trees planted throughout a parking lot are far more
effective "coolers " than those planted around the edges only
Source Adapted from Parker 1982
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Rather than
designing trees
to fit inadequate
urban spaces,
we must design
urban spaces to
fit trees.
Figure 6-17
On Pennsylvania Avenue
in downtown Washing-
ton, D.C., pedestrians
enjoy a changing land-
scape featuring boule-
vards lined with trees.
Designs of streets should change to allow more greening. Modern engineers could
use techniques like boulevards, that create a green path down the middle of the street
and double the potential planting space for trees. Each street boulevard mile can
handle about 400 trees rather than the 200 average of a normal street because the
linear curb area is doubled. Unlike the business side of the street, which presents
restrictions for trees ranging from sidewalks to power lines, the boulevard can
concentrate on landscaping.
One example is the Pennsylvania Avenue Redevelopment effort in downtown
Washington, D.C. Here, in the midst of an intensively developed urban area, the
"nation's main street" has been landscaped with a variety of large street trees, in
addition to landscaped parks and plazas in the middle of the boulevard. The devel-
opment has converted a blighted urban street into a beautiful, tree-shaded boulevard.
This accomplishment is no accident. Specific tree spaces were created both above-
and below-ground. Sidewalks and plazas were covered with blocks and bricks to allow
water and air to enter the soil below. Aeration was provided by a tile system. An
underground irrigation system was built to provide water when needed, and soil
moisture monitoring to tell when the water should be turned on. The underground
was opened up to allow tree roots to grow, rather than being tightly compacted.
Communities, in other words, have options. They are not without costs, but sound
investments that result in long-lived, healthy forests are nearly always more cost-
effective than their alternatives.
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Resources
There are many resources that can help to guide you through an urban tree-planting
program. The American Forestry Association's Global Releaf program provides
guidance on site selection and species selection to groups wanting to up the arboreal
ante in their community. Los Angeles' TreePeople has a plethora of resources to help
citizens start their own programs. Two California utilities, Pacific Gas and Electric
and Southern California Edison, have developed planting guidelines (Appendix F
includes an excerpt of a pamphlet by SCE on tree planting). There are also a number
of governmental and private tree-planting programs that can help you get started.
Refer to Chapter Five for a listing and analysis of tree-planting programs all across
the country.
In addition, there are several computer inventories available. These all-in-one
services analyze your street tree needs, develop preliminary plans for your city, and
create planting and maintenance programs. Some services also provide planting and
maintenance services.
Extending tree
lifetimes five to
ten years can
more than
double the value
they bring to the
community.
Plant New Trees, But Keep The Old
Planting young trees in your community can be an inspiring task. But
preserving old ones is an equally inspiring—and more lucrative—strategy.
Although tree care funds are most effective when spent on young and
middle-aged trees, in actual practice, removing and repairing dying or
damaged trees often soaks up most of the city budget. Indeed, one re-
searcher estimates that of the average $10.62 forestry programs spend
per tree per year, trimming amounts to about 30 percent of the budget,
tree removal about 28 percent, and planting about 14 percent.
The economic value from an urban tree rests largely in its shading,
cooling, and pollution-reducing effects. That means an urban tree continues
to gain in value so long as its crown continues to grow and spread. New
trees cannot develop these beneficial environmental effects for decades.
This means that cities that can extend life spans of urban trees through
improved care programs may find that urban forestry budgets are more
effectively used and that total values from the forest are magnified. Indeed,
extending tree lifetimes five to ten years can more than double the value
they bring to the community.
Successful preservation will depend, in part, on local legislation gov-
erning development and re-development activities. For instance, in forested
areas, developers can be required to preserve trees, and to protect them
from harm during development due to machine damage, soil compaction,
root cutting, or over-filling soils that smother tree roots. But legislation
doesn't cure all ills. Citizens have to take an active part in ensuring the
survival of their city's older trees.
—Neil Sampson
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Finally, while we cannot tell you how to plant trees in this manual (it's a subject
on which volumes have been written), we have included a short article from the
American Forestry Association at the back of this manual to act as a primer (See
Appendix E.)
Choosing Places For Light-Colored Surfacing
At present, there is little public awareness of the benefits of albedo modification.
Although most people are aware that dark colors absorb more solar heat, there is little
understanding about what constitutes high-albedo surfaces, and virtually no awareness
that massive albedo changes can affect the temperatures of entire cities or neighbor-
hoods. Similarly, few people realize that simple changes in albedo levels can reduce
home energy use by 10 to 50 percent (see Chapter Three). The lack of public awareness
of the benefits of increased urban albedo is reflected in the absence of research into
the long-term characteristics of high-albedo materials, or the development of alternative
building materials with higher albedo. Nevertheless, we can begin to identify surfaces,
methods, and potential problems with some degree of accuracy.
Walls
Some surfaces are easier to modify than others. Building walls are the simplest
and cheapest surfaces for albedo modifications. Since many buildings are routinely
painted every 10 years or so, changing the albedo of walls is simply a matter of
substituting a high-albedo paint for a darker one during repainting. Moreover, some
paint companies are now beginning to list reflectivity on their product labels.
Changing the albedo of roofs and paved areas can be more costly because it may
require the use of more expensive materials. In addition, the energy benefits may
not continue over time due to product degradation or dirt accumulation. These questions
are addressed in Chapter Four.
Roofs
For the purposes of this section, we divide roofs into those with steep or gentle
pitches. The most common materials used for steep roofs are shingles made of asphalt,
wood shakes, or concrete tile, and usually left unpainted and dark. The albedo of a
shingle roof can be changed by either painting, which is uncommon but certainly
possible, or replacing it with lighter-colored tiles during re-roofing.
Some of these options incur no additional costs. For example, installing a light-
colored shingle roof is no more expensive than installing a dark-colored one. Some
options, however, do cost more. A concrete tile made of white cement, for instance,
is considerably more expensive than a tile made of normal cement, because the white
tile is a specialty material.
Other options are expensive because they require otherwise unnecessary modi-
fications. For example, painting a roof only to improve its albedo would cost at least
an additional 20 to 30 cents per square foot. This obviously wouldn't be as cost-ef-
fective as changing color in the course of normal re-roofing.
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Gentle-pitched roofs (with slopes of less than 4 inches per foot) are generally
made of tar, bitumen, or asphalt. The costs for increasing the albedo for such roofs
are about the same as those for dark roofs. Since it is common practice to protect
the roof membrane with a protective coating, it is possible to increase the albedo
by simply using lighter-colored roofing gravel or reflective paint. If this is done during
re-roofing, increasing the roof's albedo would incur no additional costs.
Changing the albedo of a roof gives other benefits besides reducing cooling energy
consumption. First, high-albedo roofs can protect an asphalt roof from the damaging
effects of ultraviolet (UV) radiation. Second, because the high-albedo surface keeps
the underlying roofing materials cooler, the roofs will tend to slide less.
Roads And Pavements
Paved surfaces like roads, playgrounds, and school yards can be lightened either
by resurfacing or repaving. Resurfacing uses an asphalt mixed with aggregate, and
typically adds only an inch or so to the existing surface. Many cities are resurfaced
periodically to extend the life of a street or parking area. If the added aggregate is
light, a thin layer of asphalt or a chip seal is a good way to increase the albedo of
a paved surface.
Slurry seal, an aggregate of fine particles mixed with asphalt, is also often used
on paved surfaces. Slurry seal typically has low cost and low albedo, because of its
dark materials. Lighter-colored slurry seals are manufactured in Europe and have
been used on tennis courts, plazas, and road shoulders, but the costs of such seals
in the United States have not been investigated, nor have their albedos been measured.
If a paved surface is structurally damaged and must be replaced, or if a new surface
is being constructed, either asphalt or concrete can be used at equivalent costs. Re-
placing asphalt with concrete, called "whitetopping," results in a slight increase in
albedo. Rolling a light-colored aggregate onto the top few centimeters of an asphalt
cement is slightly more expensive, but produces a higher albedo, especially after
the surface has been slightly worn. The most expensive option for increasing albedo
is to use white cement for the top inch or so of a cement pour.
Summary
A variety of measures can be taken to increase the albedo of a city, including:
For Walls :
1. Use light-colored paint during routine painting.
For Roofs:
1. Replace dark-colored shingles with light-colored shingles.
2. Paint dark shingles with a lighter color.
3. Add light-colored rocks to gently-sloped roofs.
4. Add light-colored aggregate to the roofing material. This extends the life
of the roof by protecting it from UV radiation and preventing membranes
from slipping.
Changing the
albedo of a roof
gives other
benefits besides
reducing cooling
energy consump-
tion. First, high-
albedo roofs can
protect an as-
phalt roof from
the damaging
effects of UV
radiation. Sec-
ond, because the
high-albedo
surface keeps the
underlying
roofing materials
cooler, the roofs
will tend to slide
less.
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For Paved Surfaces:
1. Use a light-colored aggregate in the asphalt. After weathering and road wear,
the aggregate will be exposed.
2. Use a light-colored slurry or chip seal when resurfacing, if such materials
can be found for reasonable prices.
3. Use a concrete surface with a light-colored aggregate, instead of asphalt.
Conclusion
While vegetation and light-colored surfaces are cleaner, cheaper, and more at-
tractive than a mechanical cooling system, they do require more forethought before
being used. This chapter has given enough guidelines to begin preliminary planning.
If we are to successfully cool our communities, however, we need also commit our-
selves to communicating with other residents and business owners about vegetation
and light surfaces on a broader scale.
Further Reading
There are many resources available to help citizens plant both on their private
lands and in their communities. The American Forestry Association, the U.S. Forest
Service, state Cooperative Extension Services, and local nurseries, horticulturists,
and universities can all help you choose species and sites wisely. For specific in-
formation on landscaping to save energy and reduce heat islands, see the follow-
ing works by Heisler (1984 and 1986), Meier (1987), Moffat and Schiler (1981), and
Parker (1982). For general information on urban forestry, see AFA publications, Moll
(1989), and publications from TreePeople, Lipkis (1990), and other local groups.
In addition, the Proceedings from the Urban Forestry Conferences of the AFA are
excellent collections of writings on the physical, social, economic, and political aspects
of urban forestry.
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Ordinances
Ordinances
Fred Patterson
Why Ordinances
Once it has been determined that an urban community's temperatures are rising,
the next obvious question is "What can we do?" Heat islands are exacerbated,
however inadvertently, by the actions of thousands of homeowners, landlords, and
business owners. That means any remedy must be far-reaching to be effective.
However, because most actions that cause increased temperatures originate on
private property, policy makers need to consider issues of privacy and freedom
of choice. This can be a difficult balance to find.
In general, a strategy for lowering temperatures by planting trees and lightening
surfaces could be based on an overall plan which ensures public support and under-
standing. Education programs about the costs of increased temperatures and its possible
solutions can inspire people to participate. Education alone, however, does not guar-
antee action.
Ordinances can lend guidance and authority to broader surfacing and planting
programs. By providing a legal framework for action, setting consistent standards,
demonstrating community support (if it was put to vote), and enforcing compliance,
ordinances are effective in ways that even the best educational programs cannot be.
In addition, a well-written municipal ordinance applies to all parties equally—even
those like large, out-of-town developers with no incentive to cooperate—while taking
issues of private property and freedom of choice into consideration.
An ordinance is only useful when it complements a broader plan by providing
a legal framework for mitigation and by demonstrating community support. An
ordinance which is highly intrusive, difficult to comprehend, or difficult to follow
works against the overall program by provoking resentment and resistance. For this
reason, ordinances should mandate only those steps which the majority of citizens
consider acceptable. More intrusive or complex measures would be encouraged through
education. After citizens are familiar with the issues and stakes involved, ordinances
can be expanded to become more comprehensive.
Education alone
does not guaran-
tee action.
Ordinances can
lend guidance
and authority to
broaden heat-
island programs.
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Questions of
standards,
flexibility and
penalties are
the foundations
of any ordi-
nance, and must
be clearly
resolved before
putting the
ordinance
before the
public.
Using Existing Ordinances
Existing urban forestry ordinances provide both legal frameworks and ethical
precedents for regulating vegetation on private property. Ordinances regarding trees
have existed since the industrial revolution. Today, 70 percent of incorporated Californian
cities have some kind of tree ordinance. None are designed specifically for the mitigation
of urban heat islands, but many provisions in these ordinances apply exactly to heat-
island reduction—or could complement that reduction.
For example, many ordinances preserve existing trees and require that a minimum
number of trees be planted in each parking lot for aesthetic reasons. These trees undoubtedly
prevent some warming of the city, even though that is not the purpose of the ordi-
nance. Similarly, the Model Energy Conservation Landscaping Ordinance (shown
in Appendix D), developed by Dr. John Parker, at Florida International University,
and directed primarily towards energy conservation through landscaping, contains
all the provisions necessary for reducing the urban heat-island effect. Since any heat-
island mitigation strategy will involve trees, it is a good idea to place an ordinance
targeted at reducing heat islands within an overall municipal tree ordinance.
As of today, few, if any, albedo ordinances exist in the United States. Because
of this lack of precedent, the first mitigation step probably should not be a com-
prehensive ordinance. Albedo restrictions are an unusual reduction in the rights of
property owners. Whereas tree ordinances require property owners to take action
that beautifies and adds value to their property, albedo restrictions require homeowners
to take actions that might lessen the aesthetic value of their holdings. Such programs
engender opposition. On the other hand, an educational program encouraging al-
bedo modification can alert property owners to the monetary and health benefits
of reducing individual energy use and mitigating heat islands.
Elements Of A Heat-Island Ordinance
An ordinance designed to lower urban temperatures would do the following.
It would set explicit standards for buildings and landscaping and provide for
penalties to property owners and developers who violate these standards. It would
designate or establish an agency which will be responsible for interpreting and
enforcing the ordinance. It would provide explicit definitions of what is and is
not acceptable for use by the executing agency. It would also state the motivations
and guidelines for such standards for interpretation by courts, affected parties,
and the executing agency in cases where the standards cannot be applied literally.
The ordinance may also designate or establish a citizen group to oversee the design
of the plan which the executing agency will implement, and it may explicitly es-
tablish a city-wide heat-island mitigation program.
General Issues
Several general issues should be kept in mind during the development of this
type of ordinance. Questions of standards, flexibility, and penalties are the foundations
of any ordinance, and must be clearly resolved before putting the ordinance before
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Sample Revised Existing Ordinance
Oak Lawn Special Purpose Zoning District—Excerpts
City of Dallas, Texas (1985)
Purpose:
To permit the establishment of development standards specifically tailored to meet the
needs of this unique urban environment—an area recognized as having cultural and archi-
tectural importance and significance to citizens—standards designed to achieve buildings
more urban in form, with an attractive street level pedestrian environment, with continuous
street frontage activities in retail districts, with hidden parking, and with scale and adjacency
standards appropriate to character of adjoining neighborhood development; to restrict future
use of property from some less compatible uses; to use the existing zoning density as a
base from which to plan development and to provide for increased density as a bonus for
the inclusion of residential in mixed-use projects in commercial zones; to discourage variances
or zoning changes which would erode the quantity or quality of the single family neighbor-
hoods, or would fail to adhere to the standards for multifamily neighborhoods and commercial
areas or would fail to contribute to the overall objectives of the plan; and to require more
extensive landscape/streetscape with new construction.
Sample provisions in the revised standards:
For Multifamily—1 Standards:
Provision requiring parkway/streetscape improvements: trees planted, minimum 3-1/
2 inch caliper, 25 feet on center within first 5 feet back of curb; with 20 percent of areas,
curb to property line, designated parkway planting area and available for growth of veg-
etation; and with a minimum 4 feet width sidewalk between tree plantings and lot line.
(Parkway Landscape Permit required from the Director of Public Works)
For Multifamily—2 and 3 Standards:
Provisions requiring front yard and total site landscaping, parkway/streetscape improve-
ments, parking screens, and landscape plan submission same as Multifamily—1 Standards.
For Office—1 and 2 Standards, General Retail and Light Commercial Standards, and Heavy
Commercial and Industrial—2 Standards:
Provisions requiring parkway/streetscape improvements: minimum 3-1/2 inch caliper
trees planted 25 feet on center within first 5 feet back of curb and with a minimum 6
feet width walk requirement. (Parkway Landscape Permit required from the Director
of Public Works)
—City of Dallas, Department of Planning and Development
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the public. The manner in which these issues are resolved will largely determine
the effectiveness and intrusiveness of the ordinance. Therefore, the following issues
must be resolved, while providing local citizens with as much flexibility and privacy
as they require.
Figure 7-1.
Ordinances set standards
for a minimum level of
performance In parking
lots, for example, an ordi-
nance could establish
guidelines for the num-
ber of trees to be planted
relative to the number of
parking spaces
Performance Standards Versus Prescriptive Standards
Ordinances generally set standards for minimal performance using one of two
methods. Performance standards specify what level of performance (e.g., shading)
is required to satisfy the ordinance. One ordinance in Sacramento, California, for
example, requires tree planting that will shade 50 percent of a parking lot within
15 years. Prescriptive standards require a simple method to achieve a minimum level
of performance to satisfy an ordinance. One Los Angeles, CA, ordinance requires
that one tree be planted for every four parking spaces in a parking lot.
An ordinance need not rely exclusively on one method. Developing standards
that can be satisfied by following either a prescriptive or a performance track allow
flexibility to home owners and builders. By allowing mitigation by various strategies,
affected people can choose the method most appropriate to their circumstances.
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Ordinances
Required methods would also give benefits other than heat-island reduction. A
regulation requiring certain numbers of trees in every parking lot, for example, keeps
cars generally cooler. This reduces energy use, hydrocarbon emissions from heated
gasoline tanks, chlorofluorocarbon emissions (by alleviating the need for air con-
ditioning within the car), and occupant discomfort.
Private Rights Versus Public Responsibility
City governments have the authority to set standards designed to protect and
enhance public health, safety, morals, convenience and welfare, and they have police
powers to enforce these standards. With the exception of restrictions on noxious plants
and those constituting a fire danger, little precedent exists for intrusive regulation
of vegetation on private property. Furthermore, except for some beautification
ordinances, there is little precedent for the regulation of building color. Nevertheless,
because much of the problem of rising urban temperatures originates on private lands,
some intrusion may be necessary if a mitigation program is to be successful.
If a proposed ordinance is perceived as an unwarranted interference with a citizen's
privacy and property, it will generate intense opposition. Designing an ordinance
to fit the local temperament and to include measures which are easily followed helps
reduce that resistance. It also may help convince residents that the city has their best
interests in mind.
A good strategy in drafting provisions is to carefully select desirable measures,
and then divide them into groups, depending on how intrusive the measures are. Very
intrusive measures need not be mandated at all. Instead, they can be part of an
educational program and offered as suggestions to the public. Municipal agencies
could implement the most intrusive measures of the ordinance, such as extensive
planting requirements, or prohibitions of dark-colored roofs and parking lots. Current
residents should be subject to the least intrusive measures, such as limited planting
requirements on resale, prohibition of tree removal without a permit, and albedo re-
strictions on flat, non-visible roofs. Planned developments and existing businesses
fall somewhere in between on the spectrum and could be subject to extensive planting
requirements and some restrictions on visible roofs. Such a division will encourage
maximum reduction in the heat island, while minimizing the negative effects on un-
willing citizens, thus minimizing opposition.
Flexibility Versus Effectiveness
An ideal ordinance gives citizens a choice of strategies, while remaining effective.
Programs with a sophisticated array of options offer great flexibility, but they are
sometimes hard to understand and implement. Programs that are easy to understand,
however, may be too loose and therefore ineffective.
For instance, one way of ensuring flexibility is to use a point system. In both
California's energy conservation building code and Parker's Model Energy Con-
servation Landscaping Ordinance, any action taken to save energy earns a certain
number of points, based on the effectiveness of that strategy. The ordinance requires
a minimum number of points before a building is given an occupancy permit. This
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The Guidebook on Tree Planting and Light-Colored Surfacing
Figure 7-2.
Flexibility may be one of
the most appealing fea-
tures of a good ordinance.
When citizens can exer-
cise choice about the
types of trees or colors of
paint, they are more likely
to be enthusiastic about
meeting the require-
ments of the ordinance.
is a good system for new buildings. But the sophistication and complexity of the
point system makes it difficult to understand, which does not help the overall program.
On the other hand, if homeowners are required to plant a given number of trees
(based on house size), but not told where to put them, the trees may end up only
shading other trees and empty lots, instead of roofs, walls and air-conditioners.
One alternative to this dilemma is to require a given number of trees or shrubs
on the east, south, or west sides of a house. Property owners can pick species and
locations—within stated limits. An ordinance requiring, for example, that three trees,
chosen from a list of appropriate species, be planted anywhere within ten feet of the
east, west, or south sides of the house would be fairly simple to implement. Giving
residents the opportunity to substitute several shrubs for one tree increases the number
of choices available to residents. In general, this system allows maximum flexibility
and ease of interpretation and compliance. Any reduction in effectiveness could be
mitigated by simply requiring that more trees be planted at each household.
The costs of such a program would be minimal when compared with the total
cost of constructing a new building. However, if such plantings were required at
existing structures, the financial impact could be substantial on low-income home
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Ordinances
owners. The expense of planting several trees may total more than a month's income
for the elderly or others on fixed incomes. This is another indication that ordinance
writers must be cautious when regulating the landscaping of existing houses. If such
landscaping is required, a process for community-supported plantings or special ex-
emptions for low-income property owners must be developed. One criteria listed in
the ordinance for the granting of variances must be extreme financial hardship to the
property owner.
Citizens feel less threatened by an ordinance with more latitude, because they
retain the right to choose the manner in which they will live. Generally speaking,
if community support is less than complete, it is better to design an ordinance that
is flexible. Policymakers may find they have no choice in this matter, as people will
accept nothing less. Effectiveness will be less than complete, but it is better to have
a weak ordinance that has community support — and is part of an overall mitigation
program designed to build public awareness — than a stringent ordinance that is un-
likely to be followed—if it even gets passed.
The most effec-
tive ordinances
will reduce heat
islands by
encouraging
right actions,
not by punishing
wrong ones.
Positive Versus Punitive Ordinances
An overly punitive ordinance also is
not effective. Cities may need ordinances
to enforce heat-island reduction plans, but
the most effective ordinances can reduce
heat islands by encouraging right actions,
not by punishing wrong ones. For ex-
ample, an ordinance should emphasize
tree planting, and not financial penalties
for something like a dark roof. Similarly,
the emphasis of heat island reduction pro-
grams and ordinances need not be en-
forcement. Instead, it could be the estab-
lishment and maintenance of a program
that reduces the heat island with the en-
thusiastic cooperation of the public, not
its coerced participation.
Key Items For An Ordinance
If you have never developed an ordi-
nance before, the next section provides
a good basic guide. But you should seek
other guidance as well—either from more
experienced people in your city govern-
ment, or from various planning services
currently available.
If you already have experience with
ordinance development, this section gives
Figure 7-3.
The effectiveness of
ordinances may be
assisted by generat-
ing enthusiasm to
co-participate.
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you some ideas on viable—and sometimes necessary—provisions. Parker's ordinance
developed for southern Florida (Appendix D), also provides excellent examples of
possible provisions for a temperature reduction ordinance. Since every city has different
climatic conditions, statutory limitations and traditions, however, all examples should
be liberally interpreted and adapted to local conditions.
1. Long and short title.
"The Tree Planting and Light-Colored Surfacing Ordinance of the City of
Anytown," or "Tree and Surface Ordinance."
2. Purpose.
States the intent of the ordinance for interpretation by the voters and the courts.
For example, "To improve the health and welfare of the citizens of Anytown by
reducing the summer heat island."
3. Findings of fact (optional).
For example: "The importance of energy conservation, the effect of the heat island
on health and energy use, the possibility of energy shortages and the certainty of energy
price increases, and the effect of light-colored surfaces and trees on the heat island."
4. Definitions.
Any and all terms used, including albedo (how it's measured and what standard
is used); size of protected trees; condition of trees; protected, encouraged, and
prohibited trees, etc. When defining a parking lot, include access roads and turnarounds
and any other area of asphalt that is exposed to sunlight. If a point system is used,
terms like "cooling trees" and "cooling bushes" (that is, those that are accepted as
cooling a structure) should be clearly defined, based on minimum height and proximity
to the surface to be shaded.
5. Establishment of authority.
Establishes or designates the authority(s) that will design and/or implement the
city's program to reduce the summer heat island. Alternatively, the ordinance could
merely designate several agencies, each responsible for implementing part of the program.
For example, the department responsible for building inspections may be designated
as responsible for inspecting shading and roof albedo, while the Parks and Recreation
Department is given the task of planting and maintaining trees on city property.
If the ordinance establishes a new authority, such as a Shade Tree Board or a City
Forester, the ordinance could set qualifications for membership (e.g., "one botanist
or horticulturist, one lawyer, one architect, one builder, one forester with five years
experience, and two citizens of the community") and provide for their selection and
replacement. It would set their compensation (usually none or car fare), and also set
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the pay and qualifications of any position established—or delegate these decisions
to the shade tree authority or other authority.
The ordinance should discuss the authority of the executing agency (whether it
is a Shade Tree Board and a City Forester, or any other city agency) to issue permits
for planting and stop-work orders, withhold occupancy permits, and to enter private
property to determine compliance with the ordinance and to remove hazardous trees.
If a master plan for heat-island reduction is not explicitly included in the ordinance,
then authority to develop one can be delegated. In this case, the ordinance would
include specific guidelines for such development, including acceptable and unac-
ceptable measures for mitigation and stating what levels of intrusion onto private
property are acceptable; criteria deemed sufficient to justify variances such as extreme
economic hardship or unusually shaped property; and a discussion of to whom the
ordinance will apply.
6. Definition of responsibility.
The ordinance must define the responsibilities of the agency(s) and property
owners who participate in the mitigation program or who are otherwise subject to
the ordinance. These responsibilities may include, for instance, the planting, main-
tenance, pruning, and removal of trees on municipal, public agency, and private lands.
Similar issues must be covered for albedo, if it is addressed in the ordinance, including
the installation and cleaning of light-colored surfaces.
In general, a municipal tree ordinance should establish title to and responsibil-
ity for all trees on public lands and for trees planted on private land to satisfy mu-
nicipal requirements. An ordinance designed solely to reduce heat islands will have
a similar scope.
Liability for damage due to tree planting, including vehicles hitting trees, pe-
destrians tripping on cracked sidewalks, injury to body or property from fallen limbs
or trees, fires, and damage to sewers or utility lines is a very important issue. If it
has not been addressed by an existing municipal tree ordinance, it must be addressed
by the heat island ordinance.
7. Minimum standards.
The ordinance should set minimum requirements and specify when they must
be met. The basic purpose of the ordinance is to facilitate management of city trees
to minimize a heat island. But the ordinance need not be so restrictive that it makes
Note: Establishing a new agency is rarely easy. Legal, procedural, and
political problems can be daunting, especially for those who are inexpe-
rienced. The experience of those who have worked in tree-planting programs
or who have set up other agencies will be vital to the creation of a shade
tree or other type of tree-planting authority.
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compliance difficult and thus lowers public support and participation. Nor should
the ordinance be used to micro-manage the actions of the agencies' responsible for
implementing it.
Instead, it can set broad policy aims and give an outline of acceptable methods
of mitigation. Day-to-day management must be done according to the professional
opinion of the person given the responsibility of carrying out the program mandated,
who should be guided by the ordinance, and by any other authorized agency such
as a Tree Board. Standards specific to trees can include:
a. Species restrictions/requirements/suggestions.
A general municipal tree ordinance may include restrictions on noxious species,
species vulnerable to disease, or tall species beneath utility lines. A heat-island
ordinance may further restrict species by requiring that trees used to meet its require-
ments grow to a minimum height—if the only requirement is that a given number
of trees be planted. It also should list protected species if they are given special
consideration in the ordinance.
If any of the provisions of the ordinance are based on shading, then the ordinance
should list, or designate a resource that lists, the crown diameters of desirable species
so that citizens can plan their landscaping. The ordinance lists recommended species
along with characteristics.
b. Planting requirements.
The ordinance can specify which types of property are subject to particular
provisions and where plantings must be made on each property. The ordinance also
can specify whether existing structures are subject to its provisions, or only new
construction and remodeling. In most cities, new construction will contribute only
a small part of the problem, and so, unless existing structures are targeted, little will
be done to alleviate the problem.
As discussed above, measures such as shading air conditioners that have the largest
benefits at the least cost, should be applied to existing structures. More restrictive
measures should be applied to businesses and new construction. If a system similar to
the Model Energy Conservation Landscaping Ordinance is used, then this section should
state the minimum number of cooling trees and bushes, or the minimum number of points,
that are required for a building or a piece of property of a given size and type.
c. Prohibitions on planting.
The ordinance should prohibit planting where it blocks view of signs or natural
scenery, and where it restricts access to solar radiation, including sunlight falling
on solar collectors, on another property. Restricting solar access should be defined
explicitly as shading a given percentage of a solar collector at a given time on a
given day.
d. Protection of trees.
This area is generally a function of standard municipal tree ordinances, as are
prohibitions on planting. However, the protection of existing trees is a valuable
tool in the prevention of further urban warming. Existing trees are often large and
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Ordinances
effective shade trees, even if they are not ideally placed, historically significant,
or locally endangered.
Provisions of an ordinance that prevent significant tree clearing during devel-
opment and tree damage during construction are especially valuable. Such provisions
include a prohibition of grading beneath the canopies of desirable trees, and a re-
quirement that no trees be removed, topped, or severely pruned without a permit.
Nurseries, silviculture, nuisance trees, emergencies, and utility work should be dis-
cussed and granted limited exemptions.
Since utility workers have no incentive to preserve existing trees, an explicit
standard of tree pruning (no topping, for example, and no cutting of branches over
2 inches in diameter) should be part of the exemption.
Los Angeles county has adopted a weak prohibition against clearing historic
trees. When developers clear oak trees, which the county is trying to preserve, they
are required to make a contribution to a fund that supports the planting of oak trees
elsewhere in the county. Although mature oak ecosystems are lost, the ordinance
attempts to preserve the overall amount of trees. The heat-island ordinance should
include criteria to be used in the evaluation of exceptions to such restrictions.
No Net Loss of Forest
The "no net loss of forest" idea has been suggested in con-
nection with urban and community forests, where it is entirely
possible to think about protecting, replacing or improving for-
ests as a part of normal community growth and development.
Clearly, some forest will be lost in the process. That is to be
expected. But when development takes place on formerly open
land, there is also the opportunity to convert such land into a
community forest with a 50 percent or higher canopy cover. The
result would be a net gain of forest cover for the region. So the
question is logical: Can development ordinances in a growing
region attempt to achieve a "no net loss" goal?
One region grappling with such a question is the Chesapeake
Bay Region, where it has become widely recognized that many
of the water quality problems afflicting the Bay are really land-
based problems. The watershed, previously forested, now har-
bors millions of people, and the growth rate continues to climb.
Can the Bay Region, with better growth management controls,
support this growth without completely wrecking the Bay's aquatic
ecosystem? That question is high on the priority list of regional
leaders, and the "no net loss of forest cover" idea may be one
aspect that gets a thorough testing in the process.
—Neil Sampson
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e. Minimal standards for plantings.
The ordinance can contain a provision stating that all trees must be planted
according to specific standards of size and grade if they are to be used to satisfy the
ordinance's planting requirements. One example of such standards is the International
Society of Arboriculture's Standard Municipal Tree Ordinance. But many local or-
dinances have more explicit and restrictive standards.
Responsibility for watering and other maintenance can be assigned in Section
5 of the ordinance. This section should set minimal standards for this care.
The ordinance can also define the minimal acceptable size of the planting area for
one tree. That is, building and landscaping codes may need to be modified so that each
tree has enough root space to survive. Constricted root spaces are a common cause of
illness and death in urban trees. Standards specific to albedo modification include:
a. Surfaces to be modified.
As discussed above, if albedo modifications are required by ordinance, then they
should be limited in scope because of their unusual nature and the potential for
opposition. If you decide to include albedo measures in the ordinance, two areas that
should be considered are asphalt coverings for flat roofs, and parking lots.
Flat roofs are not very visible, so little aesthetic harm can result from an ordinance
that requires a final coating of light-colored sand. Light-colored materials are
commonly used as the final layer on roofs because they save energy and because the
roofing materials last longer when more light is reflected away from them. An
ordinance would simply require that this practice be universal. It would affect a rela-
tively small number of builders and business owners, since few single family homes
have flat roofs.
Similarly, a surfacing requirement for parking lots would impact relatively few
property owners, while providing a benefit for many. Parking lots should be an early
target of an energy conservation program, because they make up a large area of many
city centers.
Developing albedo ordinances is slightly more complicated than developing tree
ordinances. Tree planting requirements for parking lots are quite common. Surfacing
requirements designed to reduce heat buildup are not. Modified surfaces will be more
obvious—and less aesthetically pleasing—to the general public than increased tree cover.
Businesses may oppose such a provision if they think people will not like it (due to
increased brightness or increased visibility of dirt, oil and trash), or if they anticipate
increased maintenance costs on new or modified city-owned parking lots. This way,
problems can be solved, and fears allayed, before the provision is forced on businesses.
b. Initial albedo required.
The ordinance can specify a range of acceptable values on a specified scale and
the method used to determine compliance.
c. Minimal maintenance.
Since light-colored surfaces inevitably get darker as they weather and get dirty,
the ordinance may specify what level of maintenance (such as cleaning) is required
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or the required level of albedo which must be maintained. Note that policing continued
compliance adds a great deal to the cost of implementing the program.
d. Material restrictions.
Alternatively, the ordinance can restrict the materials and techniques that can
be used to satisfy the ordinance. For example, if albedo is never checked after initial
installation and no maintenance is required (which reduces the cost to the administering
agency as well as to the business complying with the ordinance), the ordinance should
prevent businesses from using materials with a short life-time.
8. Procedure and criteria for variances.
As previously discussed, the ordinance can set up a process in which variances
can be granted by the administering agency and list the criteria to be used in granting
them. This process will help to ensure that the aim of the ordinance is accomplished
while preventing avoidable harm.
For example, variances could be granted for landscaping that approximates a
natural ecosystem, regardless of the number of trees, since such ecosystems have
value beyond their potential to reduce the heat island. In many areas, for example,
native vegetation is locally endangered.
9. Process for appeals.
The ordinance can specify a procedure whereby anyone unhappy with the analysis
done by the administering agency can appeal the decision. If a shade tree board or
other citizens group is established, it can serve as a reviewing body.
10. Penalties for violations.
Penalties will vary depending on which provision is violated.
If planting is required during construction, then an occupancy permit can be denied
until the administering agency is satisfied.
If existing trees are illegally removed, then replacement should be required, along
with a fine sufficient to prevent illegal tree removal from becoming routine. A man-
dated replacement policy can stipulate that several trees replace each one illegally
removed, for example by requiring that the cumulative circumference of the replace-
ment trees be equal to the circumference of the tree removed.
A system that is easier to administer, especially if the diameter of the original
tree is unknown, is to require that a given number of trees of a minimum size be planted
for each one removed. Fines for illegal removal also encourage compliance.
If the ordinance requires a re-inspection to determine tree health, a daily fine
can be levied when required plantings are removed, dead, or dying.
Any provisions concerning the albedo of construction materials can be imple-
mented in the same way. For example, occupancy permits can be denied if required
steps are not taken, and fines levied and replacement mandated if light surfaces
are removed or darkened.
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A reduction in
urban tempera-
tures is depen-
dent on the
public perform-
ing a variety of
unaccustomed
actions.
11. Provision for feedback and modification of regulations.
A shade tree plan, or other regulations derived from the ordinance, should be
modified periodically, as experience is gained, and as the public becomes more
educated about the issue. This allows adaptation to change in the community, and
permits the regulations to be updated as needed. The ordinance should specify a
procedure, and possibly a timetable, for such changes.
Public input is vital at this stage. Public hearings should be held by the admin-
istering agency or, preferably, by the group established to guide implementation of
the ordinance such as the Shade Tree Board.
12. Effective date.
Many actions required by an ordinance for tree planting and light-colored surfacing
require considerable advance warning (for example, planting trees in parking lots),
since they must be included in construction plans from the beginning. Other actions,
such as using light-colored surfaces on roofs, can be done with little advance notice.
If a single implementation date is specified, it must be far enough in the future that
projects that already have detailed construction plans are not affected.
Alternatively, the effective date could be set earlier, with exemptions provided
to any project that has submitted detailed architectural or landscape plans for approval,
or that submits them within a given time limit such as one month.
13. Severability.
The ordinance should state that each section is independent and if any section
is found by the courts to be invalid, other sections are not affected.
Ideally, the
administering
agency should
design a work-
book that is
made available
to the public,
and which
contains the
criteria and
standards which
the agency
inspectors will
use to determine
compliance.
Other Implementation Issues
1. Published information on albedo and plantings.
A reduction in urban temperatures depends on the public performing a variety
of unaccustomed actions. This means the public needs access to information which
enables them to perform these actions: including the expected height, crown diameter,
growth characteristics, water needs, and other facts about trees. Without this infor-
mation, residents cannot choose the correct species for their needs.
In addition, those home and business owners who wish to comply with a heat
island ordinance must have a way of determining whether specific measures will be
satisfactory.
The ordinance or the administering agency can designate a resource which
discusses all the issues involved in activities for reducing urban temperatures. That
resource must be complete enough to serve as the sole information source for residents
planning their compliance.
Ideally, the administering agency could design a workbook for the public that contains
the criteria and standards which the agency inspectors will use to determine compliance.
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For instance, when the city of Davis,
California, implemented its energy con-
servation building code, it published a
workbook with numerous examples, com-
pleted forms, lists of materials and their
color value or insulative properties, and
other information to help builders comply
with the code.
Software designed to aid the selection
of appropriate vegetation can also be made
available in city offices or public libraries.
Another method of assisting compliance
is the labeling of building materials and
paint according to albedo, and the label-
ling of nursery trees according to their ex-
pected height, crown shape, and other
characteristics. This enables members of
the public who do not have a workbook
(for example, because they are not re-
quired to comply with any ordinance) to
consider the issue and make an informed
decision.
Common Problems with Ordinances
1. No maintenance required. Figure 7-4.
After trees are planted, they require The public needs access to informatlon that clear'y exPlains oomplance cntena
and standards
systematic follow-up care and water-
ing—often for several decades. Without such care, a tree may not live to maturity
or may only be a nuisance by interfering with utility lines, dropping limbs, or crack-
ing sidewalks. No trees should planted as a part of a program to mitigate a heat
island until the person responsible for follow-up care is designated. Often, this
designation should be done through the ordinance.
2. Trees too small at maturity.
If inappropriate trees are planted, they will be too small at maturity to provide much
shade, although they benefit the utility by not interfering with its lines. In addition,
trees that are too small at the time of planting may not be able to survive the rigors of
the urban environment. An ordinance should always specify the minimum size (at ma-
turity) of acceptable trees, either by specifying species or crown diameter and height.
3. Trees too small at planting.
The ordinance also can set a minimum acceptable size at planting. If trees are
too small, they will not provide continuous benefits. A related problem is that the
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The Guidebook on Tree Planting and Light-Colored Surfacing
Figure 7-5.
Trees require systematic
care and watering in or-
derto reach maturity The
individuals responsible
for follow-up can be des-
ignated in the ordinance.
minimum size of trees protected by ordi-
nance is greater than the minimum size of
tree required to be planted. An ordinance
that requires new trees be planted to re-
place mature trees removed during con-
struction may not actually protect those
new trees. In other words, a developer can
remove these new trees during later con-
struction, since they are too small to be
protected by the ordinance. This has re-
portedly occurred in southern California.
4. Landscaping is required,
but not shading.
Landscaping must be designed to pro-
vide shade if it is to prevent a significant
amount of warming. Many ordinances
require plantings of various kinds, but
even when ordinances require that trees
be planted, they don't require that they be
positioned in any particular way and they
seldom require that enough be planted to
make much of a difference.
5. Single-family homes are exempted.
It may be tempting to exempt single-family homes from a heat-island ordinance
to garner public support. This is not a particularly effective strategy, however. Single-
family homes consume a significant proportion of the electricity used for air conditioning.
They also make up a large fraction of a city's area. If an ordinance is so unpopular that
it will not be passed unless most citizens are exempted, then it is poorly written.
6. Community support is not achieved.
Community support is critical to the passage and acceptance of any new, unusual,
and far-reaching ordinance.
Community input is required at the planning stage so that potential problems are
discovered, and provisions inappropriate for the particular location are removed or
modified. All affected parties should be consulted, and the more participation a group
has in the process, the less likely it is to object to the results. If certain people are affected
by the ordinance but have not been consulted about it and do not understand its specific
provisions, they will, quite reasonably, feel threatened by it and oppose it.
Finally, community support is required after approval so that compliance and co-
operation is achieved. The wide-spread adoption of non-mandated measures, such as
those promoted by an educational campaign, are wholly dependent on community support.
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The administering agency has a great
deal of impact over how the ordinance is
viewed by the community. Consistent en-
forcement, sincere attempts to explain or-
dinance requirements to the affected par-
ties, and a reasonable delay period before
implementation all will encourage support,
or at least reduce opposition.
7. No review by legal council.
A legal review can trouble-shoot prob-
lems of legality specific to a particular
city, such as separation of powers and
improper delegation of funding decisions.
8. No long-range plans.
Urban temperatures have risen over
decades as the result of thousands of in-
dividual actions. A single ordinance will
not correct this problem overnight.
The mitigation of heat islands will
require a community-supported program
which includes an ordinance or two and an educational program. Such a program takes
time to set up and more time before it shows success. Many strategies for mitigation
are based on vegetation that takes years to mature and requires years of care. For these
reasons, a program of tree planting and light-colored surfacing requires that plans be
made further in advance than is typical in most city governments.
Community
Input Night:
TREES
Figure 7-6.
Community input at
the planning stages of
ordinances is invalu-
able to both the com-
munity and the admin-
istering agency.
Further Reading
Parker and Panzer's MECLO (shown in Appendix D) is very useful as an example
of one method of implementing the points discussed above. While it is targeted at energy
conservation, its provisions are equally useful in reducing a summer urban heat island.
Again, like any model ordinance, it must be extensively modified to meet the needs
of any particular location.
Since this ordinance does not discuss albedo, it may be used as part of a com-
prehensive heat island ordinance, or it may stand alone if albedo modification is
encouraged through education, but not mandated in an ordinance. MECLO is not
a standard municipal tree ordinance, and some concerns, such as explicit standards
for tree planting, are not discussed.
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For an example of a concise, standard municipal tree ordinance that addresses
many urban forest issues, including issues of tree survival, but does not address heat
islands or energy conservation, see Neely's work for the International Society for
Arboriculture's model.
Vine's report on Davis discusses the implementation of a number of ordinances
dealing specifically with energy conservation. For descriptions of ordinance imple-
mentation in general, see Parker, Weber, and Beatty.
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8
Conclusions
And Recommendations
Trees And Light-Colored Surfaces Can Reduce The Impact Of The Heat-Island Effect
Actions by citizens to strategically plant trees and lighten building and pavement
surface colors have the potential to reduce energy use for cooling and lower
electrical bills. This may also help lower summer temperatures in our communities,
thereby reducing the production of tropospheric ozone and improving the quality
of our environment. By reducing the generation of electrical power, these actions
also decrease the emission of carbon dioxide (CO2), the most important greenhouse
gas, and may help lower the risk of global climate change.
The Economic And Environmental Benefits
Of These Strategies May Be Significant
We are confident of the ability of trees to provide cooling benefits, but know
less about the potential value of light-colored surfaces. Likewise, we know little
about the savings produced by the two in combination, but it seems that they may
offer significant benefits at low cost or with net gains. The relative cost effectiveness
of these strategies will differ by type, region, building stock, and current conditions.
For example, planting trees for energy conservation will probably have the highest
return when applied to older homes in the Sunbelt. The single most effective im-
provement that can be made is shading air conditioners.
If implemented, these activities may have large impacts on energy savings and
pollution abatement at the national scale. A study by the National Academy of Sciences
(NAS, 1991) indicates that planting trees and lightening the color of our urban surfaces
may be able to save 50 billion kilowatt hours, or 25 percent, of the 200 billion kilowatt
hours spent annually in the United States for air conditioning. Energy conservation
at that scale would prevent the emission of 16-18 million tons of carbon (in the form
of carbon dioxide) to the atmosphere. Lastly, successful implementation may also
slow the rise in temperatures of our urban areas, which have been experiencing a
steady rise over the last few decades.
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Future Urban Scenarios
From One Scientist's Point of View
We can speculate briefly on how
much we could cool a city if we really
became concerned about the multiple
and cumulative threats of local heat is-
lands, global warming, smog, and ex-
pensive air conditioning derived from
fossil fuel. Let's look at three possible
scenarios for the Los Angeles metro-
politan area over the next fifty years:
Status Quo
We continue development as
usual, replacing orchards and fields
with blacktopped roads and parking
lots, building homes with dark colored
roof tiles, and increase our fossil fuel
use by 1 to 2 percent per year. By the
year 2050, the local heat island will
further intensify by 6°C, while global
warming will have added another 1-4°C
(Line A on graph). This will make the
city warmer than any tropical city on
the continent today.
Frozen Heat Island
In this scenario, the current inven-
tory of trees and dark surfaces is held
steady. No net loss of vegetation is
permitted. All new roofs and roadways
are tight-colored. This halts the in-
crease in the local heat island, but re-
gional warming due to the greenhouse
effect causes Los Angeles summers
to grow increasing hot and smoggy
(Line B in graph).
Heat Island Reduced to 1940 Levels
2000 2020 2040 20SO
Figure 8-1.
Three scenarios of future Los Angeles temperatures, added
to a forecast of global warming trend.
By 2050, under the business-as-usual "Los Angeles Temp
Trend" (1° per decade growth in the heat island), down-
townL.A. will be 18° hotter than it was in 1940(A). Withthe
L.A. heat island "Frozen" at its 1990 level, the city will still
be 12° hotter (B). With a vigorous program of heat-island
mitigation ("Eliminate Heat Island by 2050"), it's possible
to entirely compensate for the effects of global warming in
L.A. until somewhere around 2050 (C). Note: the global
warming trend shown assumes an exponential green-
house gas growth of 1.5 percent per year.
In this scenario, a concerted effort
is made to reduce the local heat island
fast enough to compensate for global warming (Line C on graph). This will require large-scale planting
of trees and vines, and not permitting the use of dark materials on either new construction or during
resurfacing of roofs and roadways. The local heat island is reduced, but summer temperatures in Los
Angeles stay constant because of global warming.
—Arthur Rosenfeld
Lawrence Berkeley Laboratory
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Conclusions and Recommendations
Further Research Is Required To Quantify Benefits
Although preliminary measurements and computer simulations indicate significant
potential for achieving many of the benefits we have described, more research is needed
to confirm this. The Environmental Protection Agency, the Department of Energy, Lawrence
Berkeley Laboratory, the Forest Service, the Department of Defense, and the American
Forestry Association, together with other researchers and institutions, are beginning to
measure these benefits, some of which have been difficult to quantify. As more results
become available, it seems more evident that heat-island mitigation strategies such as
trees and light-colored surfaces will significantly lower building cooling loads.
Even as this document goes to print, new data are becoming available that begin
to quantify the effects that light-colored surfaces may have on energy use. Although
a study by the Lawrence Berkeley Laboratory is preliminary and cannot be used to
generalize about other types of buildings in other climatic situations, data show that
one house in Sacramento, California realized a significant reduction in energy use for
air conditioning when its dark roof was painted white. More work must be done before
the results of this study are complete, and can be used to draw final conclusions about
the value of light-colored surfaces.
As we have discussed throughout this guidebook, a number of aspects of energy
use in communities and temperatures have yet to be explored. Following is a list of
suggestions for in-depth research:
1) Direct Effects
Field measurements are needed on the direct effects of tree cover and light-colored
surfacing in different climatic regions of the country, and on different types of buildings.
These investigations should consider different types of trees and vegetation, and changes
in the color and composition of roofs and walls. The primary focus of the measurements
should be to document the direct energy savings, both for cooling and heating.
2) Indirect Effects
Field studies are needed to verify the indirect effects on air temperature at the
neighborhood level of wide-spread planting and surface-color enhancement. A number
of computer simulations have suggested that evapotranspiration from trees and the
lowered temperatures on light-colored surfaces will produce lower ambient air tem-
peratures, which will in turn result in lowered building cooling loads. Field studies would
greatly assist in confirming these phenomena and quantifying the magnitude of the savings
possible. Additionally, research is needed to determine the extent of changes in tree
cover and surface colors that would be needed to lower temperatures in a given area
by a given amount.
3) Potential Negative Effects
Research is needed on the possible detrimental effects of increased albedo, increased
water vapor from evapotranspiration, and reduced natural ventilation potential caused
by lowered wind speed. These evaluations must be carried out specifically for each
weather type and for local conditions. The effects of increased emissions of volatile
organic compounds (VOC's) from trees, such as monoterpenes and isoprenes, should
be investigated.
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
4) Conflicting effects
Further research on the trade-off between heating costs rising'as trees (both
evergreen and bare deciduous trees) block winter sun, and cooling costs falling from
increased summer shade would be helpful. Likewise, a determination should be made
of where it is best, climatologically, to plant trees for wind-shielding to reduce heating-
energy requirements. The balance between these effects will differ among different
parts of the country. Finally, similar investigation is needed on the trade-off between
light-surfacing for cooling benefits and retaining dark surfaces in areas where energy
use is dominated by heating requirements.
5) Economic Analyses
Research is needed on the benefits and costs of tree planting and light-colored
surfacing. Does landscaping and retaining mature trees increase the sales value of
existing properties and new developments? Data are needed on the amount and type
of vegetation required to influence values, and on the magnitude of value changes
possible. We should investigate more precisely the magnitude of savings possible
from tree planting and changing surface colors in different parts of the country. This
should include quantification of the contributions of both direct and indirect effects
towards reducing energy consumption. The goal should be to assemble national
estimates, on a region by region basis, of the savings in energy, costs, and pollutants
(and the attendant savings in health and welfare costs) of instituting these changes.
Specific information is needed on the cost of different types of planting stock,
planting services, maintenance, and disposal in different parts of the country. Likewise,
data are needed on the availability and cost of high-reflectivity paints, roofing
materials, and paving materials. What is the trade-off between the initial cost, useful
life, and maintenance cost of asphalt and cement surfacing for roads and other
pavements. Are there similar trade-offs for dark and light-colored roofing materials
and paints.
6) Long Term Concerns
Perhaps the single most important factor in the success of a community tree-
planting strategy is whether or not the trees survive. Trees suffer the stresses of urban
pollution, root compaction and insufficient root space, water stress, inadequate
maintenance and care, and vandalism. Work is needed to develop ways to ensure tree
health and survival. Strategies need to be developed to successfully implement the
solutions, and to reduce stresses that contribute to or cause early mortality. Long-
term concerns about light surfaces are whether they last longer than dark surfaces,
whether the light surfaces degrade and get dirty, and what impact degradation has
on reflectivity, and ultimately, on the reliability of this strategy.
7) Evaluation of Resources
In order to more precisely calculate energy savings and financial benefits, what
mitigation strategies cost, and where they need to be done, data are needed on the
current state of infrastructure, buildings, and landscaping in the United States. National
inventories are needed of the condition of building stocks, roadways and pavements,
and community trees, conducted on a community or regional basis.
132
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Conclusions and Recommendations
8) Implementation
We need to know how best to motivate homeowners, businesses, utilities, and
local and federal governments to establish implementation programs. What incentives
are needed under varying demographic and regional conditions?
Citizens Can Affect Change If They Understand The Issues
And Know That Opportunities Exist
Research on the effects of urban heat islands is coming at a time of great public concern
about local and global environmental conditions. Air pollution, water pollution, and the
possibility of global climate change all mandate that we decrease our energy use.
At the same time, our city sizes are growing at unprecedented rates. By the year 2000,
50 percent of the world's population will live in cities, where only 14 percent lived 100
years ago. Correlating population size to heat-island intensity is still inexact. It is clear,
though, that heat islands intensify as urban areas grow. Already, urban temperatures in
this country can be 8°F hotter than those in surrounding areas, and urban temperatures
in tropical and sub-tropical countries are as much as 15°F higher than their surroundings.
Furthermore, if global temperatures continue to rise as predicted by many scientists, the
net increase in summer temperatures could be even greater.
A first step is to demonstrate the principles we have discussed here and prepare
community infrastructures. We need to learn how best to develop light-colored
roadways, to formulate and label high-reflectivity paints and roofing materials, and
to organize massive tree-planting campaigns that stress tree health and survival through
proper maintenance. Finally, the information has to be transferred to both private
citizens and public officials who serve them.
Implementing These Strategies On a Large Scale
Will Take Concerted Efforts By Many People
We can probably design programs to encourage implementation of these strategies
in the places where they will accomplish the most at the least cost. Two approaches
stand out as having particular promise.
1.) Incorporate strategic tree planting and light-colored surfacing in new devel-
opments. Design space for trees into all new construction, and design buildings
and pavements with light-colored materials.
2.) Plant trees strategically and use light-colored materials in retrofits and main-
tenance. Building and home owners can probably use light-colored roofing and
paints in the normal maintenance cycle with little or no additional cost, while
street and highway departments can use light-colored paving materials when
repaying roads. Similarly, property owners intending to plant trees can adjust
their choice of planting stock and placement to optimize the energy benefits.
Ultimately, municipalities and their residents make the decisions and take actions
to make these changes in their local environments. It is up to state and local gov-
ernments to lead on finding the best ways to integrate energy saving techniques into
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
land use, infrastructure investment, and zoning activities. Much work has already
been done by professional foresters, tree-planting groups, and local governments.
We have used the experiences of several of these tree-planting groups to show how
other interested groups might undertake similar efforts. Municipalities, businesses,
homeowners, developers, and state and local governments can all contribute to those
efforts.
A Number of Activities Can Expedite the Adoption of These Strategies
Specifically, the following tasks could be undertaken to reduce urban temperatures
and the attendant levels of energy use and smog production:
1) Undertake and expand community-wide programs for shade-tree planting and
add albedo modification. These programs can consist of volunteer programs
in conjunction with community tree planting and development groups, and public
education. Information could be made available to the public on how to or-
ganize them.
2) Promote energy conserving activities by providing information on albedo of
building products, suggestions for landscaping designs, and the energy sav-
ings possible—through retailers of building materials and trees, through for-
estry extension agents, city foresters, and contractors, and through utilities
and municipalities.
3) Provide incentives for developers to build well-arbored, light-colored, energy
efficient buildings and communities.
4) Encourage Public Utility Commissions to provide utilities with incentives to
support tree planting and surface color enhancements. Also provide infrastructure
and incentives for utility companies to promote heat-island mitigation strate-
gies through the concept of shared savings.
5) Utilities can support these activities as a way to reduce demand for peak power
and perhaps eliminate the need to build new power facilities.
6) Corporations can encourage energy conservation by sponsoring tree planting
and light-colored surfacing programs among their employees and in the com-
munities in which they and their employees reside.
7) Professional groups can create professional education materials so that their
members are conversant with new techniques for community planning, tree
planting, and other modifications to current practices.
8) Municipalities can pass tree ordinances, specify the use of light-colored pav-
ing materials in roads, buildings and renovations, provide financial incentives,
or zone for light-colored building materials in commercial areas, strengthen the
ability of roads and parks departments to plant new trees and maintain exist-
ing ones, and foster community efforts in these areas.
9) Professional schools and other educational programs could incorporate these
principles in the training of builders, engineers, architects, city and urban planners
and designers, arborculturists, foresters, and landscape architects.
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Conclusions and Recommendations
Community Design: A Long-term Perspective
Making Space for Urban and Community Trees
Planting trees is one of the easiest and most effective ways to humanize
our environment. Often, trees are quickly removed when they interfere with
signs, billboards, and lights. Communities could seek other solutions first.
The addition of trees not only makes an area more attractive, it also tends
to raise property values. Perhaps the greatest hindrance to urban tree planting
is inadequate planting space. One way to correct this problem is to "think
trees* while planning projects and determine how they might best fit. Trees
actually can be a welcome asset in housing developments, shopping cen-
ters, roads, downtown malls, parking lots, and parks. Tree planting is a cost-
effective way of creating strong community identity and visual quality.
The densities of land devel-
opment affect the amount of
space available for urban and
suburban trees. Densities over
about three units per acre (net)
may offer little space for effec-
tive tree planting. Clustered
housing concepts are prefer-
able, because exterior space is
consolidated in amounts large
enough to allow intensive tree
planting to take place. Large
lots, with two or less units per
acre, are rare these days. How-
ever, where homes must be
built in wooded or hilly areas,
this density can preserve ex-
isting trees, terrain, and top-
soil. Existing low-density resi-
dential development could be
a good place to emphasize
mass tree planting for carbon
dioxide sequestering and aes-
thetic purposes.
Here are some general
comments on considering trees
in development projects:
• Undeveloped suburban open space provides an excellent site for sig-
nificant tree planting. Ideally, open space should be preserved in direct
proportion to the density of development. Open space is not necessarily
synonymous with urban/suburban parkland.
• Parkland is frequently needed for recreational and sports purposes and
requires a high degree of landscaped development and maintenance.
Parkland is not necessarily a good place for trees or wildlife. Parkland
and open space can exist side by side with careful planning.
Figure 8-2.
Planning room for trees:
Including trees in the plan-
ning stages of develop-
ment projects where
trees are appropriate,
could add to the immedi-
ate and long-term value
of the projects. Most
people enjoy trees and
appreciate landscapes
that feature trees.
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Cooling Our Communities
A Guidebook on Tree Planting and Light-Colored Surfacing
Sewage treat-
ment plants
could be consid-
ered as poten-
tial sources of
water for major
tree planting
projects.
Figure 8-3.
The value of incentives
People who do find cre-
ative, cost-effective ways
to lighten surfaces and
plant trees for shade
could be rewarded for
their efforts with conser-
vation credits, for ex-
ample, rebates, lower
rates, and tax credits
• The present pattern of suburban development could leave more room for
ecologically useful open space. Creeks, drainage areas, rugged terrain, and
land poorly suited for building could be set aside during development as natu-
ral tree areas and managed as such after development. Such areas allow
natural growth, death, decomposition, and regeneration of trees and enhance
the restoration of natural plant and animal interrelationships. Linear open
spaces are important as cover for migrating wildlife. Without it, animals cross
streets and yards, and risk death by vehicles and domestic pets.
• Sewage treatment plants could be considered as potential sources of water for
major tree planting projects. Although there are frequently problems associated
with transporting and discharging effluent water, they are not insurmountable.
Designs to capture street run-off and use for trees are also available.
Beginning To Implement Strategies for Cooling Our Communities
Early actions might include a review of all existing means, both public and
private, to encourage planning and design that reduces fuel consumption, saves
trees, provides adequate and suitable space to plant new shade trees, and
encourages heat-reflecting surfaces. This review could cover public policies
such as taxation and subsidies policies, development regulations, public works
programs and education/research activities. Much could be learned from the
private sector, including representatives of large development firms, their
engineers, architects and landscape architects, developers of telecommunication
systems, the transportation industry, environmental groups, and non-profit
foundations and volunteer organizations.
Incentives
Following are ideas for providing incentives for individuals to participate
in the community development efforts discussed in this guidebook:
• Whenever they are applied, energy
conservation credits could be pro-
vided to homeowners who plant ur-
ban shade trees and use light-col-
ored surfaces.
• Credit could be given for homes
that incorporate wide overhanging
eaves and other passive design ap-
proaches which save energy.
• Incentives could be provided for
new and retrofit work that incorpo-
rates these energy conserving
strategies.
• Developers who create energy-ef-
ficient homes and workplaces
could be allowed additional incen-
tives for their effort.
• Power companies could provide
credits, lower rates, or rebates for
customers who incorporate these
design strategies into their homes
and businesses.
136
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Conclusions and Recommendations
Development Standards
Modifications to laws governing highways, local roads, and private devel-
opment could encourage more efficient land-use and transportation strategies.
The revised standards would encourage pedestrian-oriented neighborhoods,
allowing well-planned mixes of commercial, office, and residential uses and
narrower streets. Higher densities of development would be placed around
transit stations.
Revisions to public and private development standards also could encourage
maximum space for planting new trees and preserving existing trees. Local
government and federal lenders could require shade trees along streets and
in parking areas for all new development within their control. Other recom-
mendations include:
• Tree planting for new public roads and highways.
• Preservation of existing trees, forests, and wetlands.
• Light-colored pavement surfaces for new public roads.
• Light-colored overlays for road-resurfacing projects.
• Tree maintenance and replacement resources.
—Ralph Carhart
California Department of Transportation
Citizens Can Take Individual Actions to Improve Their Environments
As this century of rapid development
draws to a close, people have become
more and more concerned about the qual-
ity of their environment. Individuals in
communities across the United States are
planting trees and greening their homes
and work places. Planting a tree or paint-
ing a building white is a powerful first
step toward transforming our communities
into a livable, enduring inheritance for our
children. The activities we have suggested
here are simple. They give people living
in communities the opportunity to take in-
dividual actions to improve their environ-
ments in ways they will be able to see. We
hope this guidebook will spur efforts by
manufacturers and retailers of building
materials, developers, city planners, urban
and landscape designers, foresters, state
and local officials, and the private sector
to join with citizens in working toward
that goal.
U S Department of Agriculture
Figure 8-4.
Thinking aboutthe future.
Planting a single tree to-
day seems simple, but it
is a powerful first step
toward transforming
tomorrow's cities into a
livable, enduring inherit-
ance for our children
137
image:
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Appendix A
Haider Taha
Further Data on Heat Islands
Chapter 1 presented data on rising urban
temperatures and energy use in a num-
ber of cities in the U.S. and abroad. This ap-
pendix presents similar data on five other
cities. Their citations are found in the Ref-
erences section that follows Chapter 8.
Rising Urban Temperatures
Just as Los Angeles and San Francisco
average temperatures are rising, so too are
average temperatures in other California
cities rising. Oakland, for instance, though
only a few miles away from San Francisco
but sheltered from cool ocean breezes, is
warming at a rate of 0.4°F per decade. San
Jose is warming at a rate of 0.3°F, San Di-
ego by 0.8°F, and Sacramento, an inland
city, by about 0.4°F per decade. Similarly,
Baltimore is warming at a rate of 0.4°F per
decade. Figures A-l to A-5 illustrate the
temperature increases in these cities.
Oakland CA 0.42 °F/decade
70
66
I
en
< 62
0)
01
S
•* 60
58
1860 1880 1900 1920 1940 1960 1980 2000
Year
Source Based on data from Goodndge, 1989
Figure A-1.
In Oakland, California, sheltered from ocean breezes, tempera-
tures have increased 0 42°F per decade
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A Guidebook on Tree Planting and Light-Colored Surfacing
62
San Jose CA 0.3 °F/decade
i ' r
1860 1880 1900 1920 1940 1960 1980 2000
Year
Source Based on data from Goodrldge, 1989
Figure A-2.
San Jose, California is warming at a rate of 0.4? f per decade
72
70
68
San Jose CA 0.3 "F/decade
66
64
62l . 1 . r
1860 1880 1900 1920 1940 1960 1980 2000
Year
Source Based on data from Goodrldge, 19
Figure A-3.
In San Diego, California, temperatures have been rising at a rate
of Off1 F per decade.
Sacramento CA 0.36 °F/decade
60
1800
2000
Source Based on data from Goodndge, 1989
Figure A-4.
Sacramento, California, and inland city, is warming at a rate of
0.3ff"F per decade
Baltimore MO 0.37 °F/decade
82
80
I 78
2
76
74
72
70
1860 1880 1900 1920 1940 1960 1980 2000
Year
Source Based on data
Figure A-5.
Temperatures in Baltimore, Maryland have been increasing at a
rate of 037°F per decade
152
image:
Appendix B
Ronald Ritschard
The Costs of Conserved Energy
Policy makers interested in using urban trees and light-colored surfaces to mitigate
urban heat islands and their detrimental effects will also be interested in the
potential costs of that mitigation. Researchers have developed several formulas for
calculating and comparing the costs of implementing necessary measures to save
energy, to save carbon, or to save and sequester carbon. In general, they have found
that using heat-island mitigation strategies such as planting trees is competitive with
using energy efficient appliances. This appendix briefly reviews those formulas.
Saving Energy
The potential savings from investments in energy conservation are called the
costs of conserved energy, or CCE. The formula for CCE was developed to express
the economics of energy conservation and new energy supplies on a similar basis
(Meier et al., 1983). To establish the unit of cost of conserved energy (dollars per
kWh), the annualized cost of the conservation measure is divided by the annual energy
savings. The formulation is:.
CCE ($/kWh) = Capital Cost x Capital Recovery Factor
Energy Savings/year
where: capital recovery factor (CRF) is used to annualize the capital cost
of the conservation measure.
CRF is equal to d/1 - (1 + d)"
d is the discount rate and n is the lifetime of the investment
Calculating the cost of conserved energy therefore involves four variables:
1. capital cost (investment cost) of the conservation measure;
2. annual energy savings expected from the measure;
3. amortized period of investment; and
4. discount rate of the investor.
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A Guidebook on Tree Planting and Light-Colored Surfacing
Cost of Conserved Carbon
Akbari et al. (1988) modified the concept of cost of conserved energy and applied
it to the carbon savings from efficiency improvements. This new relationship, cost
of conserved carbon (CCC), is calculated by annualizing the total cost of the con-
servation investment, and dividing it by the amount of carbon saved annually.
CCC ($/Tons-Carbon, $/T-C) = (Net CCE) (1.000.000)
Carbon Burden
where: carbon burden (CB) is the amount of carbon saved in grams C/kWh
and 1,000,000 is the number of grams per metric ton.
The value of this approach is that comparisons of quite disparate conservation
strategies can be made using the CCE and CCC formulations. Planting trees, changing
surface colors, using energy-efficient appliances and lighting fixtures, and insulating
a building can be compared for cost, energy and carbon conservation efficiency. The
estimates of CCE and CCC are only as good as the data used to make them. For
example, there are many uncertainties in the costs of saved carbon and in the costs
assumptions for urban trees in general. Some of these factors will be discussed later
in this appendix.
Costs of Saved and Sequestered Carbon
The combined effects of direct carbon sequestering and the indirect fossil carbon
savings from trees were recently calculated using a further modification of the methods
described above (Krause and Koomey, 1989). The new formulation allows the
comparison of trees which save energy and trees that only sequester carbon. If it is
assumed that a properly placed urban tree can both save carbon through reduction
in electrical energy requirements as well as by direct sequestration during tree growth,
then a new formulation (cost of saved/sequestered carbon, CSSC) is possible. It is
defined as:
rwr t*rr r\ - Net (CCE) (1,000,000)
CSSC($/T-Q- SR/ER + CB
where: SR = carbon sequestration rate (g/tree-year)
ER = annual energy savings per tree (kWh/tree-year)
CB = carbon burden (gC/kWh)
The formulation of CSSC includes the net costs of conserved energy (i.e., dif-
ference between the costs of conserved energy and avoided energy costs), carbon
sequestration rate (SR), energy savings (ER), and carbon burden for those savings
(CB). For a tree which does not contribute to energy savings, the formulation is some-
what different because the main net benefit is through the sequestering of carbon
for plant growth. The cost of sequestered carbon (CSC) is thus given as:
\ - Capital Cost x (CRF)
J —
C sequestered/year
where: CRF = capital recovery factor, as given above.
154
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Appendix B: The Costs of Conserved Energy
Factors Affecting Unit Cost of Saved Carbon
There are many factors that influence the cost of sequestered carbon from tree
planting. They include seedling price, planting cost, maintenance cost (watering,
fertilizing, and protection), survival rate, soil quality and climate (which determines
the range of available species and growth rates). Trees in communities generate costs
for leaf and branch disposal, pruning, and eventually, removal and disposal. Other
important variables are the type of species planted, location (urban vs. rural), labor
costs and overhead, land cost, economic benefits other than carbon saving, i.e., soil
conservation, and energy conservation, etc., and the discount rate used in calculating
the unit costs.
For trees which contribute to energy savings, the factors affecting the cost
of sequestering carbon are the same as for trees that do not. However, since the
former both sequester carbon as part of their growth and development and save
carbon indirectly through reductions in energy use, the relevant cost factors also
include other parameters affecting energy savings, such as site suitability and space
conditioning efficiency.
Conclusions and Recommendation
In this appendix, we discuss the possible net benefits of trees for reducing energy,
and saving and sequestering carbon. These benefits are described both from the overall
perspective of the effects of trees on microclimate and mesoscale climate, as well
as from the idea of reducing the release of carbon from trees and fossil fuel power
plants. In both situations, a case can be made that trees offer many opportunities for
cooling buildings, cooling cities, saving carbon that would ordinarily be released
to the atmosphere as carbon dioxide, and maintaining the general well being of human
inhabitants.
The appendix provides analytical methods that can be used to compare trees from
the perspectives of conserving energy, conserving carbon, and saving and sequestering
carbon. The difficulty in making specific estimates resides in the lack of credible
data on the costs of planting and maintaining trees, tree survival rates, and the rate
of carbon sequestering over the lifetime of the tree. Also, keep in mind that at this
time we are unable to estimate a cost benefit of reducing stormwater or preventing
soil erosion or other such benefits. Those wishing to use these equations should
investigate the costs and biological factors applicable to their areas and use them
in the calculations.
Future research on this topic seems highly warranted. Several research topics
are recommended. First, there is a need for more precise information about the
establishment costs of tree planting programs (e.g., planting and maintenance costs,
soil quality, etc.). Second, the various limitations to massive tree planting programs
need to be identified and evaluated. As examples, the spatial and water requirements
and pollution sensitivities of different tree planting scenarios will require thorough
and well documented assessments. Also, it has recently been reported by Chameides
et al. (1988) that some tree species may affect urban air pollution in a more important
way than previously thought by their emissions of reactive hydrocarbons. This finding
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needs to be included in any long-term assessment of tree planting programs. Third,
case studies of tree planting programs need to be established that can lead to critical
evaluations, including field based measurements, of the various different parameters
described earlier. Finally, future work is needed to extend this methodology to consider
the costs and benefits of urban trees to all sectors of the economy.
References
Akbari, H., J. Huang, P. Martien, L. Rainer, A. Rosenfeld, and H. Taha, 1988. "The
impact of summer heat islands on cooling energy consumption and global
CO concentration." Lawrence Berkeley Laboratory Report No. (LBL-25179),
Berkeley, CA.
Akbari, H., J. Huang, P. Martien, L. Rainer, A.Rosenfeld, and H. Taha, 1988. "Saving
energy and reducing atmospheric pollution by controlling summer heat is-
lands." Proceedings of the Workshop on Saving Energy and Reducing Atmo-
spheric Pollution by Controlling Summer Heat Islands (LBL-27872), February
23-24, 1989, Berkeley, CA. pp. 31-44.
Energy Information Agency (EIA), 1984. Residential Energy Consumption Survey:
Consumption and Expenditures, April 1984 through March 1985, Part 2: Re-
gional Data (DOE/EIA-0321). U.S. Department of Energy, Washington, D.C.
Krause, F. and J. Koomey, 1989. "Unit costs of carbon savings from urban trees, rural
trees, and electricity conservation: a utility cost perspective." Proceedings of
the Workshop on Saving Energy and Reducing Atmospheric Pollution by Con-
trolling Summer Heat Islands (LBL-27311), February 23-24, 1989, Berkeley,
CA. pp. 92-121.
Meier, A., J. Wright, and A.H. Rosenfeld, 1983. Supplying Energy Through Greater
Efficiency. University of California Press, Berkeley, CA.
156
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Appendix C
Karina Garbesi
Estimating Water Use by
Various Landscape Scenarios
This appendix describes a plant water use system originally developed for agri-
cultural crops, but now being used for urban landscape plants. This system was
described briefly in Chapter Four. The appendix will also discuss the water-usage
implications of changing the relative coverage of lawns, trees, and shrubs.
The Crop Coefficient System for Characterizing Water Use
by Landscape Plants
Studies of the irrigation requirements of agricultural crops have provided a useful
system for describing relative water use by plants, and for estimating their evapo-
transpiration (ET) in different environments. 1 In this system, a reference evapotrans-
piration (ET0) is defined as the ET (in, for example, mm per day) of a 4 to 7 inch
tall, cool-season grass that is not water-stressed, and that is in a large field, rendering
boundary effects negligible. (UC Cooperative Extension, Leaflet 21426).
ET0 data for California are available through the Department of Water Resources
(DWR) in a number of forms: 1) monthly historic data are averaged and presented
as ET0 isolines superimposed on the state map; 2) tables of historic data are available
for many regions; and 3) ET is calculated daily based on meteorological data collected
at 90 weather stations throughout the state. This information, gathered and managed
by the California Irrigation Management Information System (CIMIS), is accessible
by computer modem and is used by some agricultural irrigators and large-turf managers
to calculate deficit irrigation requirements (i.e., watering one week makes up for
the water deficit due to evapotranspiration of the week prior, minus any contribution
from precipitation).
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Evapotranspiration for a particular crop (ETC) is determined by multiplying a
crop coefficient (Kc) by the reference ET:
(1) ETC = Kc ET0 -
In this way, crop coefficients give the relative water use of different crops.
A volumetric evapotranspiration rate (VET) can be determined by multiplying
crop ET by crop area.
(2) VET = ETC Ac = KCET0AC .
For a single tree, the volumetric rate of water use is obtained by multiplying the
crown area by ETtree, representing the total water transpired and evaporated in the
area covered by the tree.
From the perspective of an irrigator, the interesting quantity is the amount of
water that needs to be applied to meet the ET demand of the crop. Losses due to runoff
and percolation out of the plant root zone are incorporated by an irrigation efficiency
term, T| , indicating the fraction of applied water which remains in the plant root zone
available for use. The irrigation requirement, Ir, for a homogeneous crop under constant
environmental conditions is:
(3) Ir T! = Kc ET0 - P .
Where Ir is the irrigation water (mm/day) required to make up for ET losses from
the previous period which were not replaced by precipitation (P).2
Changes in the irrigation requirement due to changes in vegetation type and cover
can be calculated by taking the difference of the summed ET requirements of all crops:
(4) AIr = ( XKC, final! ffinali - 2-rKc, initial! finitiali) ETO/T1
where ffinali and finitiali denote the final and initial fractions, respectively, of the to-
tal urban area covered by the ith crop. The precipitation term, assumed unchanged, drops
out. Similarly, Kc, finali and Kc, initial! denote the final and initial crop coefficients of
the ith "crop", allowing for changes in water use due to selection of either high- of low-
water-use plants. And there are n total "crops", or plant classifications.
The summed terms can be thought of as a net crop coefficient for the region
of interest:
(5) Kn = Kci fi ,
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Appendix C: Estimating Water Use by Various Landscape Scenarios
for either the initial or final distribution. Finally, the percent change in water use
may be determined by:
\v f(v\ Kn, final - Kn, initial X 100 .
(6) AJVn(, to) -
Kn, initial
Irrigation efficiencies (h) have been measured for large turf areas. An efficiency
of 65 percent is considered to be about the best attainable. Typically, irrigation ef-
ficiencies of large-turf areas are considerably lower, around 45 to 50 percent , the
difference being lost to excessive runoff or percolation due to poor irrigation uniformity
or overly rapid or lengthy irrigation.3 Irrigation efficiency of small lawn areas such
as on median strips or bordering streets can be considerably lower if sprinklers are
not adjusted properly to limit spray area to the turf. Increasing irrigation efficiency
from 45 to 65 percent corresponds with a water savings of 20 percent without any
decrease in ET.
It appears that no studies have been made of irrigation efficiencies of urban
vegetation types other than turf. Better figures are available for agriculture. In
California about 60 percent of applied water leaves as EJ4 to groundwater; and most
of the remainder is runoff (Cooperative Extension, Leaflet 21379). Note that a relatively
small fraction of the water taken up by a plant is actually incorporated into plant matter.
In the case of a tree, for example, more than 95 percent of water taken up is lost through
transpiration (Kramer and Kozlowski, 1960).
Recent studies of the water requirements of landscape plants, which were motivated
by water scarcity in the western United States have focused on minimum rather than
optimal water requirements, while maintaining acceptable plant appearance. An
adjusted crop coefficient (AKC) was therefore developed for landscape plants, in-
corporating an allowable level of water stress. AKC is used by the California Depart-
ment of Water Resources for calculating turf irrigation requirements. In practice,
this parameter is taken as:
(7) AKC = 0.8 * Kc (Walker and Kay, 1989).
If low-water use management practices are adhered to and plants are watered
according to an adjusted crop coefficient, then evapotranspiration rates and irrigation
requirements would be calculated by equations 1 through 5 replacing Kc with AKC.
While a huge lore on plant water use exists, little of it explores urban settings.
Most studies of plant water-use are for agricultural crops, for which loss in yield
due to water stress is not tolerated. Except for some studies of turf grass, researchers
have only begun to investigate the water use of trees, shrubs, and ground covers in
urban settings.
In addition to the scarcity of reliable data, our ability to quantify the water demand
of urban landscapes is complicated by the large number of urban factors that can alter
water use. These include:
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1) The variety of plant species in urban areas (including large numbers of im-
ported and exotic plants) makes calculations of total landscape water-use
starting at the species level intractable.
2) Similarly, transpiration rates for an individual plant also vary with time of
day, season, and the life cycle of the plant. Some cease transpiring in dark-
ness, while others also stop in intense sunlight.
3) Variations in environmental and meteorological conditions strongly affect
plant evapotranspiration. Changes in light intensity, temperature, humidity,
wind, and water availability can drive plant transpiration rates from near
zero to maximum levels that can exceed even pan evaporation rates. Urban
soils are also often compacted by traffic or covered with pavement, which
can affect transpiration rates by limiting the flow of water, oxygen, and nu-
trients to plant roots.
4) Variations in landscape maintenance practices can mean large variations in water
availability, even when all other environmental factors are seemingly equal.
The sources of uncertainties outlined above make it clear that it is difficult to
attempt to precisely quantify urban water usage. However, it is possible to estimate
landscape water usage rates averaged over longer time periods—such as month—
for broad plant categories. Such an approach is adopted here, following a system used
by the California Department of Water Resources.
Data on Water Use by Landscape Plants
Table C.I presents crop coefficients for April to October (the likely irrigation
months) for some landscape plants for which measurements have been made. The
data appear to indicate a trend that grass uses more water than trees and trees use
more water than groundcovers.
Two studies currently underway will provide more data on water requirements
of non-turf landscape plants. One project is investigating minimum water requirements
of six mature shrubs and groundcovers common in urban Southern California: Hedera
helix (English ivy), Baccharis pilularis (coyote bush), Potentilla tabernaemontana
(cinquefoil), Vinca major (periwinkle), Gazania rigens (trailing gazania), and
Drosanthemum hispidum (pink ice plant).5 Preliminary results, based on the one year
of data on mature plants collected thus far, indicate that minimum water require-
ments of at least two species are consistent with the low-end Kc's given for ground-
covers in Table C.I, but that ice plant, at least, can tolerate a very wide range of
applied water.6
Another project investigating the minimum water requirements of landscape trees7,
is studying eight tree species: Liquidambar styraciflua (sweet gum), Quercus ilex
(holly oak), Ficus microcarpus (Indian laurel fig) Cupaniopsis anacardioldes (carrot
wood), Pinus radiata (Monterey pine), and one species of Phoenix and two of
Washingtonia palm. The trees under study are not yet mature, but preliminary results
are consistent with the data given above. Data from these studies should become
available in the next few years and will be a significant contribution to our quantitative
knowledge of water use by landscape plants.
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Appendix C: Estimating Water Use by Various Landscape Scenarios
Table C. 1 Monthly and Averaged Crop Coefficients for Selected Plants.3
Month Turfgrass Avocado Citrus Deciduous Liquidatnbar Groundcover
Warm Cool Warm Cool
April
May
June
July
August
September
October
Average Kc
Average AKc
,72
.79
.68
.71
.71
.62
.54
.68
.55
1.04
.95
.88
.94
.86
.74
.75
.88"
.70
.45
.50
.55
.55
.50
.45
.45
.49
.39
.52
.53
.53
.53
.53
.52
.51
.52
.42
.47
.66
.72
.72
.62
.40
.22
.54
.44
.45
.50
.55
.60
.60
.60
.55
.55
.44
.25 -
.25 -
.25 -
.25 -
.25 -
.20 -
.50
.50
.50
.50
.50
.40
Source JL Meyer and R Strohman, 1989
a Data are presented only for months during which irrigation is likely.
b. Kc for a cool season grass is defined as 1 0 by the definition of ET0 given above, this is not to be
confused with a cool season turf grass, given here Turf grass has different water requirements
because it is cut shorter, 1 to 2 inches rather than 4 to 7 inches as for the reference crop
Based on currently available data and on discussions with horticultural researchers,
we will take the following values as typical crop coefficients:
Table C.2 Average Summertime Crop Coefficients for Landscape Veg-
etation Classes. (Estimates are subject to change as new
data become available.)
Vegetation Type
AKr
grassa
trees
shrubs and groundcovers
0.8
0.5
0.4
0.6
0.4
0.3
a. Kc for grass was estimated as an average value available for cold and warm season turf grasses.
Although data on crop coefficients of landscape plants are limited, numerous ob-
servations by landscapers support the finding that grasses, in general, use more water
than trees and shrubs.8 In fact, the first principle of Xeriscape (low-water use land-
scaping) is to minimize turf area and replace it with low-water-use trees, shrubs, or
groundcovers. Not only do grasses in general want more water than trees, but it appears
that watering trees at the same level as grasses can be harmful to many trees. A report
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by the Municipal Water District of Orange County and the Department of Landscape
Architecture at California Polytechnical University lists 44 tree species, their typical
lifetimes in Southern California, and their estimated lifetimes if planted in lawns. On
average, the lifetime of trees in lawn was 42 percent of their typical lifetimes. For
one drought adapted species of eucalyptus (red-iron bark), the estimated lifetime in
lawn was only lOpercent of the typical lifetime (MWDOC, no date available).
The values in Table C.2 are useful for making first order estimates of water use
in areas for which the study plants are representative. However, in areas with primarily
high or primarily low-water-use plants, these data may be misleading. It is therefore
important to account for the actual local distribution of plants.
Another drawback of using highly aggregated crop coefficients, such as those
in Table C.2, is that they can obscure potentially important transpiration characteristics
of individual plants. For example, some drought tolerant species like ceanothus and
manzanita are dormant during the summer, during which time transpiration is mini-
mized and over watering can actually be lethal. This characteristic could be useful
for areas trying to reduce peak summertime water use.
Ideally, we would like to have crop coefficients for a wide range of species to
determine, for example, the effect of switching from high to low-water-use plants.
We would also like ET data for any given plant in various climates, so that problems
of variable adaptations to new environments could be eliminated. Unfortunately, these
data do not exist for many plants.
Until better data become available, the relative water needs of different species
can be estimated from data on precipitation received in their native habitats. MWDOC
(no date available) lists precipitation in their native habitat of 150 landscape plants
present in Orange County. These data are reproduced in Table C.3, and crop coefficients
are estimated using the crop coefficient of Liquidambar styraciflua (from Table C.I)
as a reference point. The calculation assumes that runoff and percolation from the
root zone are in the same proportion to precipitation in all habitats—so that if plant
A lives in an area which receives twice as much precipitation as plant B, it is assumed
that the water received and used in the plant root zone is twice as high.
At the end of Table C.3, the estimated crop coefficients are aggregated into average
coefficients for groundcovers, shrubs, trees and palms, and vines. These estimates
concur with the finding that trees use more water than shrubs and groundcovers. The
range of estimated crop coefficients, 1.3 - 0.04, clearly illustrates the potential for
altering landscape water needs through species choice. Note, however, that the ag-
gregated crop coefficients given in Table C.3 are somewhat lower than those given
in Table C.2. In fact the values are more similar to the adjusted crop coefficients of
the latter. This result is to be expected, since the species listed in Table C.3 are all
plants present in arid Orange County, California. It is likely, therefore, that many
were chosen because they are low-water users indigenous to water stressed environ-
ments. In addition, the vegetation in Table C.2 cannot be as neatly classified as in
Table C.I. Many of the listed species can occur as both trees and shrubs (trees/shrubs).
But no distinction is made in the data. This tends to smear distinction among classes.
Note that the average crop coefficient for shrubs plus trees/shrubs is somewhat higher
than if shrubs only are included. Similarly, the value for trees, palms and trees/shrubs
162
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Appendix C: Estimating Water Use by Various Landscape Scenarios
Table C.3. Estimated Crop Coefficients of 150 Landscape Plants
Based on Annual Precipitation in their Native Habitats.
(source of rainfall data: MWDOC, no date available)
relative estimated
water** Kc***
0.61 0.34
0.31 ,0.17
0.49 0.27
0.49 0.27
0.19 0.10
0.36 0.20
0.83 0.46
0.30 0.17
0.57 0.32
0.76 0.42
0.76 0.42
0.76 0.42
0.27 0.15
0.28 0.15
0.18 0.10
0.24 0.13
0.49 0.27
0.32 0.17
0.32 0.17
1.16 0.64
0.46 0.25
0.41 0.23
0.82 0.45
0.24 0.13
0.27 0.15
0.52 0.28
0.83 0,46
0.18 0.10
1.37 075
1.02 0.56
0.71 0.39
0.38 0.21
0.86 0.47
0.71 0.39
1.02 0.56
0.27 0.15
0.30 0.16
0.30 0.16
0.45 0.25
0.86 0.47
0 17 0.09
1.59 0.88
0.44 0.24
1.06 0.59
0.44 0.24
0.75 0.41
0.89 0.49
0.82 0.45
1.34 0.74
0.45 0.25
0.50 0.28
0.44 0.24
Veg.*
Class
6C
GC
GC
GC
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
T
T
T
T
T
T
T
T
T
T
Tree species and genus
Delosperma "Alba"
Hedera canariensis
Hedera helix
Vinca major
Acacia cyclops
Acacia ongerup
Albeiia gradiflora
Arctostaphylos densiflora
Arctostaphylos hookeri
Baccharis pilularis 'Twin Peaks"
Baccharis pilularis "Pigeon Point"
Carissa gradiflora
Ceanothus "Concha"
Ceanothus "Joyce Coulter"
Ceanothus cyaneus
Ceanothus griseus horizontalis
Cistus crispus
Cistus ladanifer
Cistus pupureus
Coprosma baueris (C. repens)
Dodonaea viscosa
Echium fastuosum
Elaegnus pungens
Encelia californica
Escallonia rubra
Grevillia lanigera
Heteromeles arbutifolia
Jasminum humile
Lantana camara
Lantana montevidensis
Leptospermum scoparium
Myrtus communis
Pittosporum tobira
Plumbago auriculata
Psidium littorale
Rhamnus californica "Eve Case"
Rhus integrifolia
Ribes viburnifolium
Rosmarinus officinalis
Syzygium paniculatum
Tecomaria capensis
Viburmum japonicum
Acacia baileyana
Acacia melanoxylon
Acacia pendula
Agonis flexuosa
Albizia julibrissin
Alnus rhombifolia
Araucaria bidwillii
Arbutus unedo
Brachychition acerifolius
Brachychition populneum
annual precip.
(inches)
31.8
15.9
25.7
25.7
9.9
18.7
43.1
15.8
29.8
39.6
39.6
39.7
14.2
14.3
9.5
12.3
25.4
16.5
16.5
60.5
24.0
21.5
42.5
12.3
14.1
26.8
43.3
9.1
71.3
53.1
36.9
20.0
44.7
36.8
53.1
14.2
15.6
15.6
23.2
44.7
8.9
82.8
23.0
55.3
23.0
38.9
46.4
42.6
69.8
23.3
26.1
23.0
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Veg.*
Class
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
T
Tree species and genus
Carpobrotus chilensis
Carpobrotus edulis
Casuarina cumminghamiana
Casuarina equisetifolia
Casuarina stricta
Cedrus deodora
Ceratonia siliqua
Chorisa specios
Cinnamomum camphora
Cupaniopsis anacardiopsis
Eriobotrya deflexa
Erythrina caffra
Eucalyptus camaldulensis
Eucalyptus' citriodora
Eucalyptus cladocalyx
Eucalyptus ficifolia
Eucalyptus globulus
Eucalyptus grandis
Eucalyptus lahmannii
Eucalyptus leucoxylon
Eucalyptus maculata
Eucalyptus nicholii
Eucalyptus polyanthemos
Eucalyptus robusta
Eucalyptus rudis
Eucalyptus sideroxylon
Eucalyptus viminalis
Ficus benjamma
Ficus macrophylla
Ficus rubiginosa
Fraxinus uhdei
Fraxinus velutina
Geijera parviflora
Ginkgo biloba
Gleditsia triacanthos
Grevillea robusta
Jacaranda mimosifolia
Koelreuteria bipinnata (elegans)
Koelreuteria paniculata
Lagunaria patersonii
Leptosperman laevigatum
Ligustrum japonicum
Liquidambar styracif lua
Magnolia grandiflora
Melaleuca linariifolia
Melaleuca quinquenervia
Olea europaea
Photinia serrulata
Pinus canariensis
Pinus halepensis
Pinus Pinea
Pittosporum phillyraeoides
Pittosporum viridiflorum
Platanus acerifolia
Platanus racemosa
Podocarpus gracilior
Podocarpus macrophyllus
annual precip.
(inches!
10.2
20,0
23.0
41.0
23.0
9.7
25.7
65.8
52.6
44.7
84.8
8.9
21.1
39.6
9.4
39.7
24.0
44.7
22.4
17.7
37.2
36.5
23.0
59.3
10.1
21.8
26.4
63.0
40.0
21.8
39.5
21.9
19.2
44.7
49.1
46.5
20.4
19.3
43.1
52.4
46.5
46.3
52.0
50.8
46.5
44.7
23.3
43.1
3.9
25.4
35.6
9.7
30.9
19.2
14.1
38.2
124.8
relative
water**
0.20
0.38
0.44
0.79
0.44
0.19
0.49
1.27
1.01
0.86
1.63
0.17
0.41
0.76
0.18
0.76
0.46
0.86
0.43
0.34
0.72
0.70
0.44
1.14
0.19
0.42
0.51
1.21
0.77
0.42
0.76
0.42
0.37
0.86
0.94
0.89
0.39
0.37
0.83
1.01
0.89
0.89
1.00
0.98
0.89
0.86
0.45
0.83
0.08
0.49
0.68
0.19
0.59
0.37
0.27
0.73
2.40
estimated
Kc***
0.11
0.21
0.24
0.43
0.24
0.10
0.27
0.70
0.56
0.47 -
0.90
0.09
0.22
0.42
0.10
0.42
0.25
0.47
0.24
0.19
0.39
0.39
0.24
0.63
0.11
0.23
0.28
0.67
0.42
0.23
0.42
0.23
0.20
0.47
0.52
0.49
0.22
0.20
0.46
0.55
0.49
0.49
0.55
0.54
0.49
0.47
0.25
0.46
0.04
0.27
0.38
0.10
0.33
0.20
0.15
0.40
1.32
164
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Appendix C: Estimating Water Use by Various Landscape Scenarios
Ve§.*
Class
T
T
T
T
T
T
T
T
TfP)
TfP)
TIP)
T(P)
TfP)
TIP)
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T.S
T?
T?
V
V
V
V
V
V
Tree species and genus
Pyrus calleryana
Quercus agrifolia
Quercus ilex
Quercus suber
Schinus molle
Tristania conferta
Ulmus parvifolia
Viburnum tinus
Archontophoenix curtninghamiana
Butia capitata
Chamaerops humiiis
Phoenix reclinata
Washingtonia filifera
Washingtonia robusta
Callistemon citrinus
Callistemon viminalis
Feijoa sellowiana
Hakea suaveolens
Laurus nobilis
Melaleuca armillaris
Melaleuca nesophylla
Metrosideros excelsus
Myoporum laetum
Nerium oleander
Pittosporum crassifolium
Pittosporum undulatum
Prunus caroliniana
Prunus ilicifolia
Prunus lusitanica
Prunus lyonii
Psidium guajava
Schinus terebinthifolius
Xylosma congestum
Acacia "Pecoffverde"
Acacia rosmarinifolia
Bougainvillea glabra
Bougainvillea spectabilis
Cissus antartica
Lonicera japonica "Halliana"
Parthenocissus tricuspidata
Wisteria sinensis
Average of all plants
Max
Min
St. Dev.
Average of GC's
Average of S's and T.S's
Average of T's, T(P's) and T.S's
Average of V's
annual precip.
(inches)
36.8
12.3
25.4
23.2
28.2
41.0
15.9
25.4
66.5
40.1
15.4
35.1
3.3
8.4
44.7
41.0
65.8
11.4
16.5
29.5
26.4
49.1
35.1
23.2
35.1
46.5
52.0
14.2
32.3
31.2
53.1
54.5
42.2
10.2
9.1
53.1
53.1
46.5
43.1
52.6
27.3
32.96
124.80
3.34
18.50
24.775
31.99
33.82
45.95
"Vegetation Classes: GC = groundcover, S = shrub, T =
""Water use is relative to that of
***kVe are ralmlatorf raiatiuo tn Kr
relative
water**
0.71
0.24
0.49
0.45
0.54
0.79
0.31
0.49
1.28
0.77
0.30
0.68
0.06
0.16
0.86
0.79
1.27
0.22
0.32
0.57
0.51
0.94
0.68
0.45
0.68
0.89
1.00
0.27
0.62
0.60
1.02
1.05
0.81
0.20
0.18
1.02
1.02
0.89
0.83
1.01
0.53
0.36
Tree, T(P) =
estimated
Kc***
0.39
0.13
0.27
0.25
0.30
0.43
0.17
0.27
0.70
0.42
0.16
0.37
0.04
0.09
0.47
0.43
0.70
0.12
0.17
0.31
0.28
0.52
0.37
0.25
0.37
0.49
0.55
0.15
0.34
0.33
0.56
0.58
0.45
0.11
0.10
0.56
0.56
0.49
0.46
0.56
0.29
0.35
1.32
0.04
0.20
0.26
0.34
0.49
Palm, V = vine
Liquidambar Styraciflua.
nf 1 imiirtamhar Sturariflna 1 = rplativp water IISR fl RR1
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A Guidebook on Tree Planting and Light-Colored Surfacing
is somewhat lower than if trees alone are included. In other words, if only species
known to belong to a given class are included, the values in Table C.3 diverge toward
the values of the adjusted crop coefficients given in Table C.2.
ET in a Multi-layered Canopy
One final issue is worth examining—the potentially important contribution to
water-use by grass growing beneath trees. In other words, real urban canopies are
multi-layered. The assumption of a single-layered canopy implicit in the fore-going
calculations might under-estimate net landscape water use. This section examines
the effect on lawn water use of shading by trees.
We will assume that the environment seen by the tree is essentially unchanged
and calculate the additional ET of the shaded lawn. A simple empirical model of
potential ET (ETp) of crops is used to estimate the change in grass ET.9 The model,
developed by Jensen and Haise (1963), is given as a function of dry-bulb temperature
(T) and net short wave radiation (Rn) at the grass surface.
(8) ETp = (0.0252 T - 0.078) Rn
where ETp is in cm of water per day, T is in degrees Celsius, and Rn is expressed
in equivalent cm of evaporated water per day. Rewriting Rn in terms of the incident
solar radiation I as 1(1-a), where a is the albedo of the grass, and using an average
value of a = 0.2 (Oke 1987, pg. 12):
(9) ETp = 0.8 (0.0252 T - 0.078) I.
Taking the total differential of ETp and dividing by ETp gives:
(10) dETp/ETp = dl/I + (0.0252 dT)/(0.0252 T - 0.078) .
So, in order to estimate the effect of the tree on ETp^rass we need to estimate
the attenuation of net short wave radiation due to the presence of the canopy and the
change in air temperature under the canopy. Taha et al. (1988) measured daytime
temperature suppression in an orchard. Within 5 m of the edge of the canopy they
measured temperatures as much as 4.5°C lower than outside the orchard. Because
we are interested in the effect of an isolated tree, under which air exchange with the
surroundings should be considerably larger, we will use a smaller value of 1°C.
We will use a simple model of exponential attenuation of light as it filters down
through the canopy (Jones 1983, pg. 31):
(11) I/I0 = e-kL,
where I0 is the intensity of light at the top of the tree canopy, L is the leaf area index,10
and k is an attenuation factor, dependent on canopy structure and sun angle. Observed
values of k range from 0.3 to 1.5 (Jones 1983, pg. 33). Kittredge (1948) lists leaf area
indices of 10 trees ranging from 2.8 to 10.7. Using even a modest leaf area index of
166
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Appendix C: Estimating Water Use by Various Landscape Scenarios
5 and a k of 0.5, the fraction of incident radiation which makes it through the canopy
(I/I0) is only 0.08. In other words, the short wave radiation the lawn sees is 92 percent
lower in the shade of the tree (dl/I = -0.92). Using this value, dT = -1°C, and T = 32°C
in Equation 9, we get an estimated reduction in ET of grass of 95 percent !
We should interpret this result as an indication that suppression of lawn ET can
be large as a result of shading. Indeed, the results suggest that the total water use
of a fully shaded lawn covered by low-water-use trees might well be lower than water
use of the unshaded lawn alone. We should not, however, put a lot of faith in the
numerical result for a number of reasons. First, an isolated tree will not provide full
shade under the canopy at all times of day. Second, vegetation might be shaded at
certain times of day by buildings regardless of the presence of the tree. 11 Third, simple
linear models like Equations 9 and 10 are not likely to be robust against large changes
in the input parameters. This can be seen by using high K and L values which results
in a reduction in ET of greater than 100 percent .
In conclusion, while planting trees above lawn is certainly not as effective in reducing
landscape water-use as planting trees without lawn, lawn water needs can be reduced
enough by shading to make planting worthwhile. The best tactic, of course, would be
to either mulch beneath the tree or to plant low-water-use groundcover or shrubs.
Sample Calculations of Changes in Landscape Water Use
and ET based on Different Planting Scenarios
In theory, changes in landscape water requirements for a given urban area can
be estimated based on the surface areas covered by different plants species. However,
few urban areas have extensive plant inventories which distinguish numbers of plants
at the species level. Although most cities now have, or are in the process of creating,
tree inventories for street and park trees, few are likely to gather a complete inventory
of trees on other public and private lands.12 Furthermore, statistics on these trees
are not likely to be representative of the rest of the urban forest for two reasons. First,
trees on streetsides and in parks which are managed by the city are likely to be chosen
from a limited list of pre-approved tree species, whereas trees planted on private lands
are not similarly controlled. Second, park and street trees make up only a small fraction
of the total urban forest. 13
More detailed biomass data is available for some areas. Miller and Winer (1984)
used random sampling to quantify species composition and dominance in the Los
Angeles Basin. The study identifies 184 species, and the number of occurrences of
each, distributed among six structural classes: broadleaf trees, conifers, palms, shrubs,
grasses, and ground covers. For 56 prominent species, total ground area occupied
and total leafy crown volume are estimated (including the average area and volume
per specimen). Others, for example Richards et al. (1984) and Dorney et al. (1984),
have investigated the composition of vegetation of some subsection of a city in detail.
This lack of data on species present in urban areas parallels the lack of data on water
use by individual species. The combination means that estimates of landscape water
use for large urban areas must generally be based on estimates of occurrence and water
use of broad classes of plants—such as grasses, trees, shrubs, and groundcovers. Different
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landscape types can then be represented by changing the relative areas covered by each
plant class or modifying water use of a given class—which in practice corresponds with,
for example, selecting low-water -use species within a class. This approach is taken
below. Changes in water use due to changes in relative areas covered are calculated
using Equation 7. And changes in landscape water demand due to selection of primarily
low-water-use plants are estimated by modifying the crop coefficients.
The initial vegetation distribution (the base case) is assumed to be 13 percent
turf, 10 percent trees and palms, and 4 percent shrubs and groundcovers. This dis-
tribution is the same as that given by Brown and Winer (1986) for the Los Angeles
Basin and was chosen as representative of vegetation in an arid western city, not as
an attempt to describe landscape water use in that city in particular. The total vegetation
coverage 27 percent of the urban area) falls within the range found by Rowntree
(1984), 24-37 percent, in his study of four eastern United States cities.
In the first analysis, the three vegetation classes are assumed to have the typical
crop coefficients given in Table C.2. Table C.4 shows the estimated changes in land-
scape ET requirements due to changes in areal cover of the three vegetation classes.
In Cases 1-4 total vegetation cover was held constant. In Cases 5-7 total vegetation
cover was increased first to 33 percent, and later to 40 percent.
Table C.4. Calculated changes in plant ET requirements for different
landscape scenarios based on crop coefficients in Table
C.2. (Estimated changes are relative to the base case.)
% of urban area covered by vegetation type
Kc Base Case Case Case Case
Case 2345
grass
trees and palms
shrubs and GC's
% veg. cover
EKC (urban)3
EKc(vegetated)b
% change in ETC
0.8
0.5
0.4
13
10
4
27
0.17
0.63
0.00
8
15
4
27
0.16
0.57
-10
3
20
4
27
0.14
0.52
-18
4
15
8
27
0.14
0.51
-19
5
20
8
33
0.17
0.52
0
Case
6
3
30
7
40
0.20
0.51
18
Case
7
0
20
20
40
0.18
0.45
5
a. Effective crop coefficient of entire urban canopy, including non-transpiring areas. De-
fined as: EKC urban = Kc.gfu.B + Kc,fut + KCiSfu.s; where Kcg is the crop coefficient for grass,
fug is the fraction of urban area covered by grass, ana similarly for trees and shrubs.
b. Effective crop coefficient of vegetated area only. Defined as:
EKC. vegetated = KC./V.Q + Kc,tf,.t + Kc,sfv.s; where Kc,g is the crop coefficient for grass, fv 8 is the
fraction of vegetated are covered by grass, and similarly for trees and shrubs.
c. Estimated change in ET calculated using Equation 7, assuming the base case as the
initial distribution.
168
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Appendix C: Estimating Water Use by Various Landscape Scenarios
Cases 2 and 3 show the effect of increasing tree cover by 50 percent and 100
percent, respectively, while decreasing grass cover correspondingly and holding shrub
cover constant. The effect is a notable decrease in ET requirement of 18 percent .
Case 4 shows the effect of increasing tree and shrub cover by 50 percent and 100
percent, respectively, and holding total vegetation cover constant. ET is reduced 19
percent. Case 5 indicates that we can double tree and shrub cover, and increase total
vegetation cover to 33 percent with no change in ET if lawn cover is reduced to
approximately 40 percent of its base value.
Cases 6 and 7 show scenarios for a total vegetation cover of 40 percent. 14 Case
6 shows ET requirements increasing by 18 percent with tree cover tripled, shrub cover
nearly doubled, and grass reduced to 23 percent of the base case. In Case 7, taken
as an extreme, all grass is removed and vegetation cover is equally split between trees
and shrubs. This represents an increase in total vegetation cover of almost 50 percent,
with only a 5 percent increase in ET demand.
Next, landscape ET requirements are calculated assuming that low-water-use spe-
cies are purposefully selected. The results are shown in Table C.5. The change in
water needs are modeled by reducing the crop coefficients for trees and shrubs to
0.3 and 0.25, respectively. This appears feasible based on the estimated Kcs for trees
and shrubs in Table C.3 Lawn Kc is assumed to remain the same since widespread
use of water-conserving warm season grasses seems unlikely for landscaping purposes
since these grasses tend to be brown and dormant in the winter time.
Table C.5. Calculated changes in plant ET requirements for different
landscape scenarios based on crop coefficients for low-
water-use vegetation.8 (Estimated changes are relative to
the base case shown in Table C.3.)
% of urban area covered by vegetation type
Kc C2 C3 C4 C5 C6 C7
C8 C9 CIO
grass
trees and palms
shrubs and GC's
% veg. cover
Kc (urban)
Kc (vegetated)
% change in ET
relative savings (%
0.8 8
0.3 15
0.25 4
27
0.12
0.44
-31
)b 21
3
20
4
27
0.09
0.35
-45
27
4
15
8
27
0.10
0.36
-43
24
5
20
8
33
0.12
0.36
-30
30
3
30
7
40
0.13
0.33
-23
5
0
20
20
40
0.11
0.28
-36
31
7
30
10
47
0.17
0.36
0
—
13
10
4
27
0.14
0.53
-16
—
13
15
9
37
0.17
0.46
0
—
a. All column headings as in Table C.4, except where specified otherwise.
b. Water savings in Table C.5 relative to Table C.4:
|% change in ET from Table C.4.) - (% change in ET from Table C.5.)
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Cases 2 through 7 assume identical vegetation distributions in Tables C.4 and
C.5. The relative savings (Table C.5) show how much water is saved in each case
if low-water-use plants are used. These estimates indicate that water savings are large.
Even Case 6, which assumes a tripling of tree cover from the base case and an almost
50 percent increase in total vegetation cover, still results in a decrease of water re-
quirements of 23 percent, over the base case of Table C.4. The savings of low-water-
use plants in this case is 41 percent. Case 8 indicates that tree coverage could be tripled,
shrub coverage more than doubled, and total vegetation increased to 47 percent, while
still retaining more than half of the lawn area, with no increase in ET demand. Case
9 recalculates water requirements for the base case configuration using low-water-
use plants. The savings is estimated at 16 percent. Lastly, Case 10 indicates that with
lawn at the base case level, ET could remain constant, while increasing trees and shrubs
by 50 percent or more if low-water-use trees and shrubs are used.
A comparison of the estimated average tree Kc's in Tables C.2 and C.3 suggests
that the crop coefficients used in Table C.4 might be somewhat high for western cities
which have already preferentially incorporated low-water-use trees. If this is true,
then the relative savings of adopting low-water-use plants could be considerably lower
than those shown on the bottom line of Table C.5. That is, the crop coefficients might
already be closer to those used in Table C.5 than those in Table C.4, so that the relevant
changes in water use would result from changes in vegetation class distribution (trees
and shrubs vs. lawn) rather than by changes in species choice within a vegetation
class. Answers to these questions can be settled only at a regional level, with better
information on the actual species present, their numbers and water use.
Despite these uncertainties, it is reassuring to find that the estimated water savings
in Tables C.4 and C.5 are consistent with landscaper's estimates of the water conservation
potential of Xeriscape design. Savings from full implementation of all of the principles
of Xeriscape design are estimated at up to 70 percent (Swearengin 1987). This figure
includes a savings of 10 to 20 percent from irrigation efficiency, not considered here.
Savings from limited lawn areas and low-water-use plants, then, could be as high as
50 to 60 percent. A detailed study by Nelson (1987) of seven multi-family dwellings
with mature landscapes and a total of 548 dwelling units, reports an average water savings
of 54 percent by water conserving landscapes relative to traditional landscapes.
Because individual trees are likely to have their greatest impact on energy savings
by shading single family houses, we must consider typical conditions in which we
find trees next to houses. In many cases the tree canopy will overlie lawn area rather
than replace it, so we ought include the water used by the shaded lawn in our areal
estimate of net water use.
Endnotes
1 Although strictly speaking plants do not evapotranspire. However, following the convention for
agricultural crops, we use evapotranspiration of a plant to indicate the transpiration plus evaporation
which occurs on or under the plant canopy.
2 A more sophisticated model would include returns of water by condensation (dew) which might be
important in areas with high atmospheric moisture content and large diurnal temperature swings.
3 Interview with Gary Kah, President, AgTech Associates, Dec. 19, 1989. Agtech developed the landscape
water auditing program for the California Department of Water Resource's Office of Water Conservation.
For a summary of audit results, see DWR (1989).
170
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Appendix C: Estimating Water Use by Various Landscape Scenarios
4 This corresponds with an n of 0.6, assuming that water which is not lost to percolation or runoff is
left to meet the ET demand of the crop.
5 The Principal Investigator of this study is Dennis R. Pittenger, Botany and Plant Sciences Department,
UC Riverside. The project is being carried out by researchers at the University of California at Riverside
and the University of California Cooperative Extension Service
6 Interview with D. R. Pittenger, Nov. 29, 1989. (See proceeding note.)
7 Interview with Janet Harten, Irrigation and Soils Specialist, Department of Soil and Environmental
Sciences, University of California, Riverside, 11/27/89. Project by the University of California,
Cooperative Extension Service.
8 Althou-gh this is true in general, there are trees, especially riparian species adapted to growing with
their roots in groundwater, which use a lot of water. Also, in high winds, with tree crowns exposed
and grass areas sheltered, the ET of the exposed trees can be driven above that of the underlying lawn,
or even above that of ground-level pan evaporation.
9 Potential ET is the rate of ET of plants experiencing no water stress.
10 The leaf area index is the total leaf area divided by the horizontal projection of the tree canopy.
11 Preferential shading and sheltering of understory plants could result in the ratio of the water demand
of trees to low-growing vegetation being elevated in suburban areas where trees are likely to form a
windbreak, and understory vegetation receives combined shelter from both trees and buildings. When
better water use data from controlled experiments on individual landscape plants become available it
would be worthwhile correcting water consumption estimates of tall trees during windy conditions in
suburban areas.
12 Interview with Rowan Rowntree, head of Urban Forest Research, U.S. Forest Service, Jan. 19, 1990.
13 This is supported by data from Richards et al. (1984) from a study in Syracuse, New York. The authors
found that while parks and streetsides comprise about 9 and 7 percent of the total urban greenspace,
respectively, residential greenspace alone constitutes 48 percent of the total.
14 Earlier studies indicate that this amount of vegetation is achievable in a city. Similarly, Richards
et al. (1984) report total greenspace in Syracuse, New York, as 58 percent . Rowntree (1984) found
potential growing space for urban trees of 55 to 66 percent in four eastern US cities.
15 The per dwelling savings of the water conserving landscapes averaged $75 per dwelling unit per
year, with 38 percent of the savings from water alone. In addition, considerable savings on labor, fer-
tilizer, fuel, and herbicides (25, 61, 44, and 22 percent , respectively) were found.
References
Brown, D.E. and A.M. Winer (1986) "Estimating Urban Vegetation Cover in Los
Angeles," Photogrammetric Engineering and Remote Sensing, 52(1): 117-123.
Dorney, J.R., G.R. Guntenspergen, J.R. Keough, and R.Stearns (1984) "Composition
and Structure of an Urban Woody Plant Community," Urban Ecology, Special
Issue edited by R. Rowntree, 8(1/2): 69-90.
DWR (1989) Annual Report-July 1988 to October 1989 Landscape Water Management
Program, Office of Water Conservation, Department of Water Resources, State
of California, Sacramento, CA.
Jensen, M.E. and H.R. Haise (1963) "Estimating Evapotranspiration from Solar
Radiation," Journal of the Irrigation and Drainage Division, Proceedings
of the American Society of Civil Engineers, 89: 15-41.
Jones, H.G. (1983) Plants and Microclimate, Cambridge University Press, Cambridge,
England.
Kittredge, J. (1948) Forest Influences, Dover, New York, NY.
Kramer, P.J. and T.T. Kozlowski (1960) Physiology of Trees, McGraw-Hill Book
Co., New York, NY.
171
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A Guidebook on Tree Planting and Light-Colored Surfacing
McPherson, E.G. (1989) "Vegetation to Conserve Water and Mitigate Urban Heat
Islands," In: Controlling Summer Heat Islands: Proceedings of the Workshop
on Saving Energy and Reducing Atmospheric Pollution by Controlling Summer
Heat Islands; K. Garbesi, H. Akbari, and P. Martien (Eds.), Lawrence Berkeley
Laboratory, Berkeley, CA, Report No. LBL-27872, pp. 53-69.
Meyer, J.L. and R. Strohman (1989, August) Handbook for Irrigation Evaluation and
Scheduling, University of California Cooperative Extension, University of
California at Riverside.
Miller, P.R. and A.M. Winer (1984) "Composition and Dominance in Los Angeles
Basin Urban Vegetation," Urban Ecology, Special Issue edited by R. Rowntree,
8(1/2): 29-54.
MWDOC (no date) Landscape Water Conservation Guidelines for Orange County,
Prepared for the California Department of Water Resources, by the Municipal
Water District of Orange County, the Department of Landscape Architecture,
California Polytechnical University, Pomona, and EDAW, Inc.
Nelson, J.O. (1987) "Water Conserving Landscapes Show Impressive Savings,"
Xeriscape News, Jan./Feb. [National Xeriscape Council, Inc., 940 E. Fifty-
first St., Austin, Texas 78751-2241]
Oke, T.R. (1987) Boundary Layer Climates, Methuen, New York.
Richards, N.A., R.R. Mallette, R.J. Simpson, and E.A. Macie (1984) "Residential
Greenspace and Vegetation in a Mature City: Syracuse, New York," Urban
Ecology, Special Issue edited by R. Rowntree, 8(1/2): 99-125.
Rowntree, A.R. (1984d) "Forest Canopy Cove and Land Use in Four Eastern United States
Cities," Urban Ecology, Special Issue edited by R. Rowntree, 8(1/2): 55-67.
Swearengin, R. (1987) "Water Saving Flow with Efficient Irrigation, Good Practices,"
Xeriscape News, Nov./Dec. [National Xeriscape Council, Inc., 940 E. Fifty-
first St., Austin, Texas 78751-2241]
Taha, H., H. Akbari, and A. Rosenfeld (Submitted) "Heat Island Oasis Effects of
Vegetative Canopies: Micro-Meteorological Field-Measurements," Submitted
to Theoretical and Applied Climatology.
UC Cooperative Extension (no date) "California's Water Resource," Cooperative
Extension, University of California, Division of Agriculture and Natural Re-
sources, Leaflet 21379. (Can be obtained through ANR Publications, University
of California, 6701 San Pablo Ave., Oakland, CA 94608-1239. (415) 642-2431.)
UC Cooperative Extension (no date) "Determining Daily Reference Evapotranspiration
(ET0)," Cooperative Extension, University of California, Division of Ag-
riculture and Natural Resources, Leaflet 21426. (Can be obtained through
ANR Publications, University of California, 6701 San Pablo Ave., Oakland,
CA 94608-1239. (415) 642-2431.)
Walker, R.E. and G.F. Kay (1989, January) Landscape Water Management Handbook,
Version 4.1, Prepared for Office of Water Conservation, Department of Water
Resources, State of California.
172
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Appendix D
Sample Ordinance
Comprehensive Model Energy Conservation Landscaping Ordinance
The intent of the Comprehensive Model Energy Conservation Landscaping Or-
dinance is to apply energy conservation landscaping principles to conventional
landscaping ordinances. Minimum landscape standards are set forth for residential,
commercial, industrial and public areas, as well as for off-street parking and other
vehicular use areas.
The positive impact that landscaping can have upon space cooling requirements
of buildings has been documented in recent years. Air conditioning requirements
can be reduced by as much as 40 to 50 percent during the hottest parts of the cooling
season by using properly designed landscaping. The use of energy conservation
landscaping which yields minimum energy savings is penalized.
Preservation of desirable trees and shrubs to meet reforestation requirements
is also rewarded through the credit system. The preservation of such vegetation is
desirable for two reasons: 1) reduced costs for the purchase and installation of new
specimens, and 2) the retention of native canopy, especially of large, often irreplace-
able, trees.
Energy conservation is the intent of substantial shading requirements for off-
street parking and other vehicular use areas. The cooler ambient air temperatures
resulting from shading would lessen the need to air condition vehicles. Furthermore,
reduced heat collection by such paved surfaces should impact positively upon air-
conditioning requirements of nearby buildings.
A street tree program is outlined, reflecting the desirable consequences of shading
public rights-of-way, pedestrian paths and bike paths. Such shading provides a cool
microclimate, encouraging the use of these paved areas. Increased use of these areas
John H. Parker
Susan Panzer
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could result in reduced use of vehicular transportation. Furthermore, reduced heat
collection by these paved areas would reduce heat gain of nearby buildings.
Finally, standards designed to protect solar access are established. The use of
solar insolation to heat water and to passively heat buildings can significantly reduce
the use of nonrenewable sources traditionally used for these purposes. Measures must
be taken to assure access to this valuable energy source.
SECTION 1. TITLE
This ordinance shall be known and referred to as the "Comprehensive Model
Energy Conservation Landscape Ordinance."
SECTION 2. INTENT
The intent of this ordinance shall be to assure the preservation of and provision
for vegetation associated with the development or redevelopment of structures and
parking areas with (locality)., in accordance with the best principles of environmental
management, site planning and, most particularly, energy conservation, in order to
protect, maintain, and enhance the well being of the citizens of (locality). It is intended
by this ordinance that landscaping shall be used wherever possible to reduce the overall
level of energy consumption by structures and heat gain by parking areas through
modification of microclimatic temperatures. In addition, it is the intent that this
ordinance shall encourage the preservation of desirable native trees and shrubs, which
the community is in danger of losing, and which are best suited to the (local area)
environment, thereby requiring less energy input for maintenance.
SECTION 3. FINDINGS OF FACT
The (local agency) of (locality) finds that:
A. The installation and maintenance of landscaping areas is not only desirable but essential
to promote the health, safety, welfare and general well being of the community, and
the requirement of the same constitutes a proper use of police power.
B. Vegetation, if properly utilized, offers the possibility of greatly decreasing the
energy used in cooling buildings which are less than three stories in height by
shading walls and windows and by reducing ambient temperatures in and around
buildings via evapotranspiration. A single mature tree releases about 100 gallons
of water per day into the atmosphere, providing the cooling equivalent of nine
room air conditioners operating at 8000 Btus per hour for twelve hours per day.
C. Trees and other vegetation:
1. absorb large amounts of carbon dioxide and return oxygen to the air, a vital
ingredient for life;
2. precipitate dust and other paniculate pollutants from the air;
3. abate noise pollution;
4. add beauty to streets, roadways and developed areas;
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5. provide an invaluable psychological counterpoint to man-made urban settings;
6. become a valuable property asset that can affect the value and saleability
of the land;
7. provide habitats for wildlife;
8. increase the amount of unpaved surface area, allowing for more efficient aqui-
fer recharge.
D. Native vegetation is adapted to local diseases, pests, soil and climate, thereby
requiring the least amounts of pest control, fertilizer and water. Thus, native veg-
etation is generally the most energy and cost efficient vegetation to be used.
E. Exotic vegetation can crowd out native vegetation, increase the use of fertilizers
and water and degrade water quality.
F. Uncontrolled removal of vegetation before, during and after site alteration, as
well as lack of protection of vegetation during construction activities, may have
an adverse impact upon the ecological balance by:
1. radically changing the microclimatic temperatures of immediate areas, re-
sulting in increased ambient temperatures and, as a result, increased energy
consumption for space cooling;
2. accelerating the natural processes of erosion, sedimentation and runoff.
G. Replacement of vegetation at site alterations stabilizes the soil, reduces erosion,
and enhances the beauty, quality and viability of the environment;
H. The quality of the environment can be maintained and the level of energy consumed
can be minimized if proper techniques for preservation, protection, and restoration
of native and non-competing vegetation is carried out at development sites;
I. The shading of paved areas will reduce the maximum ambient temperatures of
such areas by approximately 10°F. By thus reducing heating loads within paved
areas such as parking lots, vegetation can minimize the need to air condition ve-
hicles. Such vegetation can also limit solar insulation absorbed by paved surfaces,
resulting in lower ambient temperatures in areas surrounding paved surfaces.
Such reduction in ambient temperatures may minimize the need to air conditioning
structures adjacent to said paved surfaces. The use of trees to shade public rights-
of-ways also creates a more pleasant environment, encouraging the use of pe-
destrian paths and bikeways.
J. The utilization of energy conservation landscapes yields large reductions (up
to 50 percent) in energy consumed for air conditioning buildings.
K. The climate modifying effects of vegetation is usually maximized during those
periods in which energy consumption for air conditioning is also at a maximum.
L. Landscaping of structures is particularly effective during hot summer afternoons
when electrical utility demand peaks, thus reducing kilowatt-hour usage, electric
bills, and the need for new power plants.
M. During the cooling season, attempts to reduce heat gain must focus on using trees
and shrubs to shade (in order of priority) 1) the west and 2) the east and south exposures.
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N. Based upon potential energy conservation impact on a building, a priority listing
of the areas for the provision of shade during the cooling season-are as follows
(from highest to lowest):
1. Windows
2. Air conditioners
3. Insulated roofs
4. Wall areas immediately adjacent to air conditioners
5. Other walls (in order of priority);
a. west
b. east and south
6. Horizontal surfaces adjacent to air conditioners
7. North walls
8. Solar absorbing surfaces within twenty feet (20') of the building.
9. Ground within five feet (5') of the building
10. Other adjacent ground area.
O. Energy conservation landscaping should focus on the shading of windows since
more heat is gained through windows than through any other structural component
of a building.
P. The use of landscaping to shade air conditioners can increase the operating
efficiency of said air conditioners by 4-10 percent during the warmest periods
of the cooling season.
Q. The hours of significant direct solar heat gain are:
1. West exposure - 2:30pm to 7:30pm
2. East exposure - 7:30am to 12:00pm
3. South exposure - 9:30am to 5:30pm
R. Trees to be used for energy conservation should be planted so that within ten (10)
years the canopy will be within a) five feet (5') of west or east walls or overhangs
or b) three feet (3') of south walls or overhangs. Shrubs to be used for energy
conservation should be planted within five feet (51) of west, east, or south walls
(and to a lesser extent, north walls.) so that after a period of four (4) years, the
shrub will extend within one foot (!') of the wall. If vegetation is placed at
distances greater than the above, a belt of sunlight can fall on the lower part of
the wall, increasing ambient air and wall temperatures.
S. Reductions in heat gain through walls and windows is maximized when trees,
shrubs and ground cover are combined in the landscape plan.
SECTION 4. OBJECTIVES
In order to protect, maintain and enhance both the immediate and long term health,
safety, economic stability and general welfare of the present and future citizens of
(locality), this ordinance has the following objectives:
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A. To promote energy conservation by encouraging the use of trees and shrubs for
cooling through the provision of shade and the channeling of breezes;
B. To require the landscaping of buildings, areas adjacent to buildings and parking
areas in order to facilitate energy conservation due to a cooler microclimate;
C. To promote and protect property values within the community by creating a more
aesthetically pleasing environment;
D. To promote the use of and protect, restore and maintain the native vegetation of
the community, if deemed desirable;
E. To aid in stabilizing the ecological balance in the community by contributing
to the processes of air movement, air purification, oxygen regeneration, ground
water recharge, and storm runoff retardation, while at the same time aiding in
the abatement of noise, glare, heat, air pollution and dust;
F. To prevent unreasonable destruction of the communities' existing tree canopy;
G. To prevent damage to and unnecessary removal of protected and/or desirable
vegetation during the construction process.
SECTION 5. DEFINITIONS
A. Microclimate temperature modifications: the alteration of ambient air temperatures
within a small geographical area by natural or artificial means.
B. Solar insolation: the amount of solar radiation that reaches a particular area of
the earth.
C. Ambient temperature: the temperature of the air within a given area.
D. Energy Conservation Landscaping: landscaping specifically positioned to minimize
energy used for a) space cooling, by providing shade, cooling via evapotrans-
piration or channeling of breezes during the cooling season, or b) heating, by
acting as "living insulation" and channeling breezes during the heating season.
E. Solar access: the ability of a structure or area to receive the full effects of solar insolation,
without interference by other structures, vegetation, or any other impediment.
F. Exotic Vegetation: any species of plant not native to (locality), or that areas' par-
ticular soil type, climate, geology. However, in this ordinance, the term "exotic
vegetation" shall be limited to vegetation which satisfies the above definition
but which, in particular, has been or may be harmful to the native vegetation or
ecological systems of (local area).
G. Native Vegetation: any species of plant considered to be indigenous to (local area).
H. Tree: any self-supporting woody plant which usually produces one main trunk
with many branches.
I. Shrub: a self-supporting woody perennial plant of low stature characterized by
persistent stems and branches springing from the base.
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J Hedge: groups of three or more shrubs whose branches intertwine and/or come
in very close contact with one another so that, for all intents and purposes, the
shrubs form a continuous mass.
K. Site alteration: any significant change in the use or appearance of any land
including, but not limited to, the clearing, removal or destructing of vegetation,
dredging, filling, draining, grading or any other disturbance of the natural to-
pography of the land.
L. Dripline: a somewhat circular line determined by the outside end of the branches
of a tree or shrub, projected vertically to the ground.
M. Landscaping: living plant and natural material purposely positioned and/or
maintained for functional and/or aesthetic reasons.
N. Right-of-way: public lands set aside for public traverse.
O. Pervious area: ground which allows water to percolate down through it.
P. Energy Conservation Tree: a tree qualifies as an energy conservation tree if it
complies with the following standards:
1. the tree is west, east or south of the building in question;
2. the tree dripline will extend within 1) five feet (5') of west or east walls or
overhangs or 2) three feet (3') of south walls or overhangs within 10 (10) years
of the issuance of occupancy or use permits.
Q. Energy Conservation Shrub: a shrub qualifies as an energy conservation shrub
if it complies with the following standards:
1. the shrub is placed within approximately five feet (5') of west, east or south
walls (as first priority) or north walls (as a second priority) so that the outer
edge of said shrub shall reach within approximately one foot (I1) of said wall
within four (4) years of the issuance of occupancy or use permits.
2. the shrub shall be of a species which can be projected to reach a minimum
height of four feet (4') within four years of the issuance of occupancy or
use permits.
R. Cooling Season: in Florida, between June 1 and September 30.
SECTION 6. ENFORCEMENT
This ordinance shall constitute a minimum standard and shall apply to (local area)
pursuant to Section 8. The (local area) shall be the administrating agency and rep-
resentatives of said agency shall inspect the landscaping of all development and
redevelopment and no Certificate of Occupancy or Use or similar authorization will
be issued unless the landscaping meets the requirements herein stipulated; the (local
agency) shall re-inspect said landscaping at the intervals stipulated below to assure
compliance with the intent of this ordinance.
a. Parking lots: One (1) year and three (3) years after the issuance of Certificate
of Use.
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b. Other Vehicular use areas: One (1) year after the issuance of Certificate of Use.
c. Building: One (1) year after the issuance of Certificate of Occupancy or Use.
If said landscaping is not in compliance with the requirements stipulated in this
ordinance, the owner shall be given a period of time, not to exceed thirty (30) days,
within which to comply with appropriate requirements. After a period of not more
than thirty (30) days the site shall be re-inspected. If the landscaping still fails to
meet the applicable requirements, fines shall be leveed against the owner(s) of said
property in the amount of $ . per day of non-compliance.
If any tree for which credit was given pursuant to Section 18 of this ordinance
is not alive and healthy one year after occupancy and use permits have been issued,
it shall be removed and replaced with the tree or trees which originally would have
been required.
SECTION 7. LANDSCAPING PLAN
A. It is the responsibility of an applicant to include in the Landscape Plan sufficient
information for the (local agency) to evaluate the environmental characteristics
of the affected areas. The Landscape Plan shall contain maps, charts, graphs,
tables, photographs, narrative descriptions and explanations, and citation to sup-
porting references, as may be appropriate to communicate the information required
by this section.
B. The proposed Landscape Plan shall be submitted to (local agency) for approval,
and shall include at a minimum:
1. The name and address of the owner of the land for which the development
or site alteration is planned;
2. A description of how vegetation to be preserved will be protected during and
after construction;
3. A map showing:
a. any buildings or other structures
b. the trees and other vegetation to be preserved, indicating size, species
and location;
c. the proposal for landscaping and revegetation;
d. the shadow pattern the vegetation would be expected to cast on the struc-
ture between 9 am and 5pm on August 6 within five (5) years of the
issuance of the building permit or the shadow pattern the vegetation would
be expected to cast at 3pm on August 6 within vehicular use areas after
ten (10) years of the issuance of the use permit;
e. the areas that will be covered by impervious surface;
f. proposed rights-of-ways and utility easements;
g. a legend of orientation
4. A maintenance guide which shall be supplied to owners;
- 5. Any other information which the developer or the (local agency) believes
is reasonably necessary for an evaluation of the development.
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C. All landscaping shall be installed according to the plans and specifications
as submitted and approved by (local agency) before a Certificate of Occupancy
or Use will be issued.
SECTION 8. APPLICABILITY OF LANDSCAPING PLAN REQUIREMENT
A. Unless exempted pursuant to subsection B, a Landscape Plan must be submitted
and approved:
1. at the same time a site development plan is submitted;
2. at the same time a site development plan is altered;
3. before the transfer of title when existing development is resold;
4. before a building permit is issued for the reconstruction or enlargement of
existing buildings;
5. once three (3) years have passed after the implementation of this ordinance
and existing parking and other vehicular use areas have not conformed with
the requirements herein stated.
B. Exemptions: The following development activities are exempt from Landscape
Plan requirements:
1. Minor landscaping maintenance, such as trimming of trees, shrubs, yard mow-
ing and gardening;
2. Routine maintenance or improvement within an established highway, railroad
or utility right-of-way;
3. The operation of nurseries operating in their ordinary course of business;
4. The use of any agriculturally zoned land for the purpose of growing plants,
crops, trees, and other agricultural or forestry products, raising livestock,
or for other bona-fide agricultural purposes;
5. Parking areas for single-family residences.
C. Variances: The (local agency) may grant a written variance from any requirement
of this ordinance using the following criteria:
1. The implementation of the requirements herein stated would constitute an
unconscionable economic burden; or
2. There are special circumstances applicable to the subject property or its in-
tended uses; and
3. The granting of the variance will not otherwise significantly impair attainment
of the objectives of this ordinance.
SECTION 9. LANDSCAPING QUALITY
Plant materials used in conformance with the provisions of this ordinance shall
conform to the Standards for Florida No. 1 or better as given in "Grades & Standards
for Nursery Plants," Part I and Part II (latest edition), State of Florida, Department
of Agriculture, Tallahassee, or equal thereto. Grass sod shall be clean and reasonably
free of weeds and noxious pets or diseases. Living shade trees of a leaf or flowering
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variety and/or shrubs shall be provided in accordance with the landscape quality
standards hereinafter stated:
A. Tree Standards:
1. The required trees shall be at least eight (8') feet [five (5') feet for residential
sites] in overall height upon planting and shall be graded Florida No. 1 or
better, according to "Grades & Standards for Nursery Plants," Part I and Part
II, (latest edition), State of Florida, Department of Agriculture, Tallahassee.
Furthermore, trees shall be species having an average mature spread of crown
of greater than ten (10') feet [fifteen (15') for vehicular use areas] in this
geographical region and having trunk(s) which can be maintained in a clean
condition over five (5') feet (not applicable for residential sites) of clear wood.
2. Palm trees may be utilized in place of the required shade trees in parking
areas only if an individual specimen exhibits a mature crown of at least fifteen
feet (15') in diameter. Palm trees of smaller mature canopies may not be
grouped to meet the above canopy requirement.
3. Species should be those with moderate to dense canopies.
4. Trees must be long-lived and known to do well in urban environments.
5. Native species are to be emphasized.
6. The following trees shall not be utilized.
a. members of the Ficus family with extensive root systems.
b. malaleuca (Malaleuca leucodendra)
c. Brazilian pepper-tree (Schinus terebinthifolius)
d. toog (Bischofia javanica)
e. Australian pine (Casuarina equisetifolia)
f. poison wood (Metopium toxiferum)
g. schefflera (Brassaia actinophylla)
h. castor bean (Ricinus communis)
B. Shrub Standards:
1. Shrubs shall be at least twenty-four inches (24") in height immediately upon planting.
2. Native and non-competing species are to be emphasized.
C. Vines: Vines shall be a minimum of thirty inches (30") in length at planting time
and may be used in conjunction with fences, screens, or walls to meet physical
barrier requirements as specified.
D. Ground Cover: Ground covers used in lieu of grass in whole or in part shall be
planted in such a manner as to present a finished appearance and reasonably
complete coverage within one year after planting.
E. Lawn Grass: Grass areas shall be planted in species normally grown as permanent
lawns in this geographical area. Grass areas shall be at least twenty-five percent
(25%) sodded or seeded. Solid sod shall be used in swales or other areas subject
to erosion.
F. Mulches: Mulches shall be applied at a depth of two inches (2") within the dripline
of trees and shrubs at installation, unless said dripline is covered by lawn grass.
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SECTION 10. TREE REMOVAL PERMIT REQUIREMENTS
No person shall cut down or cause to be cut down, destroyed, removed, relocated
or destructively damaged any tree without first obtaining a permit from (local gov-
ernment} as herein provided.
A. Required fees and application content.
1. Permission for removal, relocation or replacement of trees shall be requested
by written application to the (local government) in the form provided by the
(local government} and accompanied by the required fee as set forth in
subsection B(2).
2. Tree removal fees:
a. Non-agricultural land $ per tree.
b. Agricultural land: $ per tree.
Recognizing that the production of food is essential for the existence and
health of the population, and that, where agricultural use of land is
continuous, it can provide employment and income for the population
indefinitely, and also taking note of the large number of tree removals
which agricultural use, by its nature, necessitates, the fee to be charged
applicants who seek to destroy trees in conjunction with an agricultural
purpose shall be charged a reduced fee. This reduced fee, however, is
to be charged only upon the applicant's submitting to the (local govern-
ment) a covenant running with the land for a term not less than five (5)
years, indicating that the land noted therein shall not be utilized by the
owner for any purpose other than an agricultural purpose. Said covenant
shall be promptly filed with the appropriate officer for recording in the
same manner as any other instrument affecting the title to real property
and may only be released prior to its termination by written instrument
of the (local agency) releasing the owner from the terms agreed to. The
release shall only be made to the owner, however, upon payment to the
(local agency) of the permit fees that would have been charged for a non-
agricultural tree removal permit at current charges, less the amounts
actually paid for the permit at the time of application.
3. Application for said permit may also be required to contain a legible plot or
site plan, in as many copies as required by (local agency) for review and pro-
cessing, drawn to the largest practical scale showing the following:
a. Location of all existing or proposed buildings, structures, improvements
and site uses, properly dimensioned and referenced as to property lines,
yard setback areas and spatial relationships.
b. Location of existing or proposed utility services.
c. Location of all existing trees, designating those to be removed, relocated,
or replaced. Groups of trees in close proximity may be designated as
"clusters" with the estimated total number noted. The name, common or
botanical, height and caliper size of those trees to be removed, relocated,
or replaced shall be shown on the site plan.
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d. Information required in (c) above for trees proposed to be removed,
relocated or replaced shall be summarized in tabular form on the plan,
and shall include a statement of reasons for such removal, relocation
or replacement.
4. Application for permit shall be reviewed by the (local government) which
may include visual inspection of the subject plot or site and referral of
the application to such departments or other agencies having interest to
determine the effect upon the public welfare, adjacent properties, or public
services and facilities.
B. Conditions for permit.
1. Removal. No permit shall be issued for tree removal unless one of the fol-
lowing conditions, as determined by the (local government) exists:
a. A site plan submitted by the applicant shows that a proposed structure,
permissible under all applicable laws and regulations, can be situated
on the subject parcel only if specific trees are removed or relocated.
b. The tree is located in such proximity to existing or proposed structures that
the utility or structural integrity of such structures is materially impaired.
c. The tree materially interferes with the location, servicing or functioning
of public utility lines or service.
d. The tree obstructs views of oncoming traffic or otherwise creates a sub-
stantial traffic hazard.
e. Any law or regulation requires such removal.
2. Relocation or replacement.
a. As a condition to granting a permit, the (local government) shall have
the option to require the applicant to relocate or replace a tree being
removed at his expense, either within the site or with the concurrence
of the (local government) on public or private land within reasonable
proximity to the site, including the relocation to any public land in the
city retaining for future use, or donating to any citizen or group of citizens,
for any purpose in the public interest and welfare, as approved by the
(local government).
b. A replacement tree shall be of a type and species having shade potential
and other value, at least equal to that of the tree being removed, and shall
meet the landscaping standards established in Section 9. The replacement
tree shall not be of the type specified in Section 9, subsection A (5).
C. Exemptions to Permit and Fee Requirements:
1. The types of trees specified in Section 9, subsection A (5).
2. Owner-occupied properties developed for detached single-family usage, pro-
vided that where a tree is to be removed from said property without being
relocated, the (local government) shall be notified and given the option of
relocating the tree elsewhere at no cost to the property owner.
3. Utilities franchised by the (local government) may remove without permit
or fee, after prior written notice to and approval by the (local government).
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trees which endanger public safety and welfare by interfering with utility
service, provided such utilities cooperate with the city to preserve such trees
by relocation or replacement in the same vicinity or as determined by the city
for the best public benefit; except that where such trees are on owner-occupied
properties developed for detached single-family usage, disposition of such
trees shall be at the option of the property owner, subject to the provisions
of subsection D(2).
4. During emergency conditions caused by a hurricane or other disaster, the
provisions of this section may be suspended by (local government) until the
end of said emergency period.
5. All licensed nurseries, botanical gardens, and commercial grove operations
shall be exempt from the provisions of this sections, but only in relation to
those trees which are planted and growing for the sale to the general public
in the ordinary course of said licensee's business.
6. Public land.
SECTION 11. PROTECTION OF PRESERVED TREES
A. To receive credit for the preservation of an existing tree, the following requirements
must be met:
1. The entire area within the dripline of the tree shall be naturally preserved
or provided with pervious landscape material and shall be maintained at its
original grade with no trenching or cutting of roots in this area. Within this
area, there shall be no storage of fill or compaction of the soil, as from heavy
construction equipment, or any evidence of concrete, paint, chemicals, or
other foreign substances in the soil.
2. Unless otherwise authorized by the tree removal permit, no soil is to be re-
moved from within the dripline of any tree that is to remain at its original
location.
3. The tree shall not be damaged from skinning, barking, bumping and the like.
4. There shall be no evidence of active insect infestation.
5. There shall be no impervious surface or grade change within five feet (5')
of the trunk.
6. Cutting and ditching for underground utility lines shall be done in such a way
as to preserve and protect the root systems of trees.
B. Trees destroyed or receiving major damage must be replaced by trees of equivalent
environmental value as specified by the enforcement agency before occupancy
or use, unless approval for their removal has been granted under permit.
SECTION 12. LANDSCAPE STANDARDS FOR OFF-STREET PARK-
ING AND OTHER VEHICULAR USE AREAS
All areas used for the parking or display of any and all types of vehicles, boats
or heavy construction equipment, whether such vehicles boats or equipment are self-
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propelled or not, all land upon which vehicles traverse the property as a function
of the primary use, hereinafter referred to as "other vehicular uses", shall conform
to the minimum landscaping requirements hereinafter provided, save and except for
those areas used for parking or other vehicular use areas under, on, or within buildings.
A. Landscaping requirements for Off-Street Parking Areas.
1. Interior Landscaping
a. At least ten percent (10%) of the gross lot area of all parking areas shall
consist of interior landscaping.
b. Enough shade trees shall be planted so that fifty percent (50%) of the
gross lot area shall be covered by canopy within ten (10) years.
c. The required number of trees shall consist of the number required to meet
the above standard, as long as there is at least one tree for every 75 square
feet of interior landscaping.
d. Interior landscaping should consist of a mix of vegetation, including,
but not limited to, trees, shrubs, and ground cover.
2. Perimeter Landscaping
a. All paved ground surface areas other than public right-of-way, de-
signed to be used for parking an movement of vehicular traffic, except
on property used only for single-family residential lots, shall be separated
by a strip of landscape development from any boundary of the property
on which the paved ground surface is located. Such strip of land-
scape development shall be developed in accordance with the fol-
lowing requirements:
i. The strip of landscape development shall contain a wall, fence, hedge,
or dense vegetation to a height of three feet (3'), except where the
adjoining property is zoned for single- or multi-family residential
use, in which case the required height is six feet (6T).
a) If a hedge or other dense vegetation is used, the hedge or vegetation
shall be installed with plants of sufficient size and spacing as to attain
a height of three feet (31) and an opacity of seventy-five percent (75%)
within three (3) years of planting [four years (4) if a six foot (6') hedge
is required]. If the hedge or vegetation is not in compliance with the
above height and opacity requirements within three (3) years after
planting [four years (4) if a six foot (61) hedge is required], the hedge
or vegetation shall be completed with mature plants or replaced with
a wall or fence in compliance with this sub-section.
b) If a wall or fence is used, it shall be at least seventy-five percent
(75%) opaque, with any open spaces or non-opaque areas evenly
spaced and not concentrated so as to produce gaps or large holes.
A wall or fence must be made of brick, stone, concrete block, pres-
sure-treated wood, or similar materials, in accordance with prevailing
building industry standards for appearance, soundness, safety, and
resistance to disease and weather.
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B. Other Vehicular Use Areas.
1. At least ten percent (10%) of the gross lost area shall consist of landscaping.
2. Enough shade trees shall be planted so that thirty percent (30%) of the gross
lot area will be covered by canopy within ten (10) years.
3. The required number of trees shall consist of the number of trees shall consist
of the number required to meet the above standard, provided there is at least
one tree for every seventy-five square feet (75') of required landscaping.
C. Existing Parking Areas.
1. Where an off-street parking area, or other vehicular use area existed as of
the effective date of this ordinance and such off-street parking area or other
vehicular use area is enlarged in area, volume, capacity of space occupied,
landscaping requirements, as herein specified, shall be met for the total (old
and new) area, volume, capacity, or space so created or used.
2. Within three (3) years of the effective date of this ordinance, all existing off-
street parking and other vehicular use areas shall conform to the requirements
herein stated.
D. Right-of-Way Visibility
1. When an access way to parking areas and other vehicular use areas inter-
sects a public right-of-way or when the subject property abuts the inter-
section of two (2) or more right-of-ways all landscaping within the trian-
gular areas described below shall provide unobstructed cross-visibility at
a level between thirty inches (30") and six feet (6'), provided, however, trees
having limbs and foliage trimmed in such a manner that they do not ex-
tend into the cross-visibility area shall be allowed, provided they are lo-
cated so as not to create a traffic hazard. Landscaping except required grass
or ground cover shall not be located closer than three feet (3!) from the edge
of any access way pavement. The triangular areas above referred to are:
a. The areas of property on both sides of an access way formed by the in-
tersection of each side of the access way and the public right-of-way line
with two (2) sides of each triangle being ten feet (10') in length from the
point of intersection and the third side being a line connecting the ends
of the other two (2) sides.
b. The area of property located at a corner formed by the intersection of
two (2) sides of the triangular area being thirty feet (30') in length along
the abutting public right-of-way lines, measured from their point of
intersection, and the third side being a line connecting the ends of the
other two (2) lines.
SECTION 13. STREET TREE PROGRAM
A. Subdivision Street Tree Requirements.
1. Developers of subdivisions shall be required to provide shade trees within
five feet (5') of the right-of-way of each street, pedestrian path and bikeway
constructed with the subdivision. The trees shall be planted at such distances
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whereby a complete canopy will shade the width of the entire street, pedestrian
path or bikeway within ten (10) years. Tress shall conform with Landscaping
Quality Standards established in Section 9.
or
2. Subdividers shall be required to deposit a sum equal to the cost of the pur-
chasing, planting and required maintenance for the first two (2) years of the
above required street trees with the (local agency). These monies shall be
used by the municipality to comply with the requirements established in
subsection A (1).
B. Municipal Street Requirements.
1. Street Right-of-Ways.
a. Medians in divided right-of-ways shall be planted with shade trees, where
possible, spaced so that a canopy covering fifty percent (50%) of the
divided right-of-ways will exist within ten (10) years.
b. City and county right-of-ways within the municipality shall be rated ac-
cording to the following priorities for the establishment of street trees:
i. First Priority: Streets, pedestrian paths and bikeways which are used
frequently or have the potential for frequent use. For example, those
streets, pedestrian paths or bikeways which lead to stores, schools
and recreation areas, as well as other popular destinations.
ii. Second Priority: Streets, pedestrian paths and bikeways which lead
to first priority streets, pedestrian paths and bikeways.
iii. Third Priority: Other municipal right-of-ways, pedestrian paths and
bikeways, including residential streets.
C. Street Tree Committee Formation.
1. A Street Tree Committee shall be established by the municipal government
and shall be charged with categorizing streets according to and within the
above priorities (for example, among first priority streets, pedestrian paths
and bikeways, some are more frequently used than others). The committee
shall then work with the (local agency) to develop a reasonable schedule for
the establishment of street trees based upon (a) the priorities stated in sub-
section B and (b) cost factors.
D. Residential Street Tree Program.
1. The municipality should make every effort to encourage property owners
to participate in a residential street tree program.
2. The majority of the property owners of an area abutting any street may request
the establishment of street trees.
3. The property owners should be responsible for (a) the full cost of purchasing
said street trees, or (b) a percentage of the purchase price, with the balance
subsidized by the municipality. In both instances, however, the (local agency)
would be responsible for installation of the trees, initial maintenance, and
education of the homeowner about the necessary care of said tree.
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4. Shade trees shall conform with the Landscaping Quality Standards established
in Section 9.
5. Shade trees shall be planted within five feet (5') of right-of-ways, pedestrian
paths or bikepaths.
SECTION 14. LANDSCAPING INCOMPATIBLE LAND USES.
A. As a condition of obtaining any development permit for any of the following
incompatible land uses, there shall be provided a landscape buffer strip where
indicated, according to the standards hereinafter provided.
1. Residential use other than detached, single-family homes: Along an common
boundary with property in actual conforming use or zoned as single-fam-
ily residential;
2. Office or commercial use: Along any common boundary with property in
actual conforming use or zoned as residential, including mobile home parks
and mobile home subdivisions.
3. Mobile home parks and mobile home subdivisions: Along a common boundary
with property in actual conforming use or zoned as any other residential type.
4. Industrial use: Along any common boundary with property which is neither
in actual conforming use or zoned for industrial use.
B. The required buffer shall be a strip of landscape development at least five
feet (5') in width, which shall be developed in accordance with the following
requirements:
1. Said buffer shall contain a wall, fence, hedge or dense vegetation to a height
of six feet (6') within four (4) years, and said vegetation shall be at least
twenty-four inches in height upon planting.
a. When the buffer is between property used for an office, commercial or
industrial use and property in actual use or zoned for single-family resi-
dential, a solid masonry wall shall be required;
b. When the buffer is between office use and single-family residential, the
(local agency) may permit, as a special exception, the substitution of a
hedge or dense vegetation for the masonry wall if a hedge will provide
equivalent protection to the single-family residential use. The following
shall be considered before such exception is granted:
i. The scale of the office use and the adjoining uses;
ii. The traffic generated by the office use;
iii. The location of structures on the office site;
iv. The existing natural features and vegetation of the site;
v. The proposed exterior lighting and hours of operation of the proposed
office use;
c. Whenever a wall or fence is used, and is not required to be solid, it shall
be at least seventy-five percent (75%) opaque and any open spaces or
non-opaque areas shall be evenly spaced and not concentrated so as to
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Appendix D: Sample Ordinance
produce gaps or large holes. The wall or fence must be made of brick,
stone, concrete block pressure treated wood, or similar materials, in
accordance with prevailing building industry standards for appearance,
soundness, safely and resistance to disease and weather.
2. Within the buffer strip required by this section there shall be planted
shade trees spaced so that no more than thirty-five lineal feet (35') separate
their trunks. None of these trees shall be planted at a distance greater
than five feet (5') from any adjoining paved ground surface. The shade
trees used shall be from an approved List of Shade Trees maintained
and kept by (local agency).
SECTION 15. MINIMUM ENERGY CONSERVATION LANDSCAP-
ING DESIGN STANDARDS FOR THE SHADING OF BUILDINGS
A. Unless otherwise shaded by vertical or horizontal projections, 1) all west win-
dows shall be shaded by vegetation between approximately 2:30pm and 7:30pm
during the cooling season; 2) all east windows shall be shaded by vegeta-
tion between 7:30am and 12:00pm during the cooling season; 3) all south
windows shall be shaded by vegetation between 9:30am and 5:30pm during
the cooling season. These requirements shall be met within five (5) years of
the issuance of occupancy permits.
B. Unless otherwise shaded, air conditioners, and horizontal surfaces within eight
feet (8') of them shall be extensively shaded by vegetation between 8:00am
and 6:00pm on August 6. This requirement shall be met within three (3) years
of the issuance of occupancy or use permits.
C. Trees to be used for energy conservation should be placed so that within ten
(10) years the canopy will be within 1) five feet (51) of north walls (as a second
priority) so that the outer edge of said shrubs should reach within one foot (I1)
of said walls within four (4) years.
D. Tall shrubs should be placed within five feet (5') of west, east or south walls
(as a second priority) so that the outer edge of said shrubs should reach within
four (4) years.
E. Wherever possible, trees and other forms of landscaping shall be used to shade
the entrances and pedestrian paths of commercial, office and public buildings
so as to reduce ambient temperatures and heat load.
F. Where possible, trees and other forms of landscaping should be used to direct
winds and breezes so as to naturally ventilate those structures which have
appropriately positioned windows, thereby providing a more comfortable
microclimate.
G. In all cases, consideration shall be given so as to provide for the optimum place-
ment of landscape materials in order to reduce energy used for space cooling
of buildings.
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SECTION 16. PREVIOUS AREA REQUIREMENTS.
A. In addition to landscaping requirements for vehicular use areas and the separation
of incompatible land uses, the following figures represent the percent of gross
lot area that shall remain pervious:
1. Single-family and duplex residential 30%
2. Multi-family residential 40%
3. Commercial and office 20%
4. Public land use 30%
5. Industrial 20%
SECTION 17. LANDSCAPING REQUIREMENTS FOR BUILDINGS.
At least 80 percent of the required pervious area shall be covered by tree and shrub
canopy, with at least percent of the requirement consisting of shrubs. Section 18 es-
tablishes a landscaping credit system, based upon tree and shrub area, to be used for
complying with this requirement.
SECTION 18. LANDSCAPING CREDIT SYSTEM.
A. Tree Credit System.
1. To calculate credit for a given tree (whether planted or preserved), multiply
the estimated canopy area by the appropriate credit factor. The credit factor
is determined by (a) whether or not the tree is an energy conservation tree
as specified in Section 5, and (b) tree location relative to building walls.
Table D-1. Tree credit.
Estimated canopy within 10
years of planting or
building permit issuance
Diameter
15'
20'
30'
40' or greater
Area
176 sq.ft.
314 ' "
710 " "
1250' "
non-energy
conserving
trees
.8
.8
.8
.6
CREDIT FACTORS
energy conserving
E, SE, S
1,
1.
1.
.8
trees
W, SW,NW
1.2
1.2 ,
1,2
1.0
Additional Credit.
a. If a tree shades a paved, heat-collecting surface, additional credit for said
tree shall be given. To qualify for additional credit for shading heat-collecting
surfaces, a tree's dripline must be within three feet (3') of said surface within
five (5) years if the tree is west, southwest, east or southeast W, SW, E, SE)
of said surface. If the tree is south of said surface, the tree dripline must reach
the heat-collecting surface. The heat-collecting surface must be within twenty
feet (20') of the building it is associated with. If a tree meets the above
requirements, the following credit shall be given:
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Appendix D: Sample Ordinance
Table D~2, Additional Credit
Location relative to heat-collecting surface Additional credit
W, SW, SE, E 10%*
South 5%*
*percent of the area of said tree
Thus, if a tree meets the above requirements and is W, SW, SE, or E of
a heat-collecting surface, additional credit equal to ten percent (10%) of the
area of said tree shall be added to the credit calculated in Section 18 (A).
3. If a tree shades an air conditioner, additional credit for said tree shall be given.
To qualify for additional credit, the tree canopy must shade both the air con-
ditioner and the ground within eight feet (8') of the air conditioner. Further-
more, the air conditioner must be shaded between the hours specified below.
If a tree meets the above requirements, the following credit shall be added
to the credit calculated in Section 18 (A).
Table D-3. Credit for hours air conditioner is shaded.
Hours Air Conditioner Tree Location Relative
Is Shaded To Air Conditioner Additional Credit
2:30pm-7:30pm
7:30am-12:00pm
9:30am-5:30pm
W, SW
E, SE
S
20%
10%
10%
B. Shrub Credit System
1. To calculate credit for a given shrub, multiply the estimated shrub area by the
appropriate credit factor (see table below). The credit factor is determined by whether
or not the shrub is an energy conservation shrub as specified in Section 5.
Table D-4. Shrub credit.
Estimated diameter Estimated area CREDIT FACTORS
within 4 years of within 4 years non-energy energy
planting* of planting* conservation conservation
2'
3'
4'
5' or greater
3' sq. ft.
7' sq. ft.
12' sq. ft.
20' sq. ft.
.6
.6
.6
.6
1.
1.
1.
1.
*rounded to nearest whole number
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2. Additional Credit.
a. If a shrub also shades an air conditioning unit four or more hours during
a summer day, additional credit equal to ten percent (10%) of the area
of said shrub shall be added to the credit calculated in Section 18 (D).
SECTION 19. PROTECTION OF SOLAR ACCESS.
A. The proposed landscape plan by its approval shall not result in the shading of
a solar collector or south facing windows of a neighbor's property between 9:00am
and 3:00pm on January 21.
B. In choosing the species of trees and shrubs, and the placement of such vegetation,
the effect on existing or future solar access of neighborhood properties shall be
considered.
SECTION 20. MAINTENANCE OF LANDSCAPE MATERIALS.
A. All landscaping, landscaped areas, landscape development, buffer areas and trees
required by this ordinance shall be maintained and used in the following manner:
1. Plant material. All required plant material shall be maintained in a healthy,
vigorous, disease and pest-free condition, through proper and efficient
watering, fertilizing, pest and disease management, pruning, or be replaced.
2. Irrigation. All landscaped areas shall be provided with an irrigation system
or a readily available water supply located within one hundred feet (100').
Where practical, and where cost is not prohibitive, drip irrigation systems
should be installed.
3. Where practical, and where cost is not prohibitive, "natural methods of pest
and disease control should be employed.
SECTION 21. SEVERABILITY.
Each separate section, subsection, clause or provision of this ordinance is deemed
independent of all other sections, subsections, clauses or provisions herein, so that
if any of the same be declared invalid, all other sections, subsections, clauses or
provisions thereof remain valid and enforceable.
SAMPLE CALCULATION OF LANDSCAPING REQUIREMENTS
UTILIZING CREDIT SYSTEM
Example based upon an 8000 sq. ft. residential lot
Example 1: Pervious area requirement = 30% of 8000 or 24,000 sq. ft
Tree requirement = 75% of 2400 or 1800 sq. ft.
Shrub requirement = 5% of 2400 or 120 sq. ft.
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Appendix D: Sample Ordinance
Tsble D~5. Example calculations of landscaping requirements utilizing credit
system,
All examples based upon an 8,000 sq. ft. residential lot
Example #1: Pervious area requirement - 30% of 8000 or 24,000 sq. ft
Tree requirement - 75% of 2400 or 1800 sq. ft.
Shrub requirement - 5% of 2400 or 120 sq. ft.
Tree requirement:
two e.c.* 20' trees west of bldg.
one e.c. 30' tree east of bldg.
also shades air conditioner
one n.e.c.** tree
also south of driveway
Credit
754
710
71
251
15
TOTAL sq.ft. 1801
Actual
Area
628
710
1652
Shrub requirement:
Example #2
Tree requirement:
Example #3
Tree requirement:
six e.c. 2' shrubs north of bldg.
thirteen e.c. 3' shrubs west, east
and south of the bldg
three n.e.c. 4' shrubs
22 shrubs Shrub credit:
two e.c. 30' trees west of bldg.
also shades air conditioner
one e.c. 20' tree east of bldg.
one e.c. 20' tree west of bldg.
one n.e.c. 15' tree
TOTAL sq. ft
two e.c. 40' trees west of bldg.
also shades driveway
one e.c. 20' tree west of bldg.
one n.e.c. 15' tree
TOTAL sq. ft
13.5
91
18
122.5sq.ft.
Credit
850
142
314
377
140
1823
Credit
1250
62
370
140
1822
Actual
Area
710
314
314
176
1514
Actual
Area
1250
314
1564
e.c. = energy conserving
* n.e.c. = non-energy conserving
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Appendix E
Gary Moll1
The Best Way to Plant Trees
We at the American Forestry As-
sociation propose that the new
decade inaugurated this year be called
the Decade of the Tree.
During the 1990s major changes
are needed in public policy and per-
sonal lifestyle to improve the ecologi-
cal health of the planet. Tree planting
is one of the simplest ways to start the
decade on the right foot.
Perhaps no other action is more
direct: Plant a tree and cool the globe.
This call to action by the American
Forestry Association offers each of us
an opportunity to change the direction
of our personal lifestyle.
Planting trees around our own
homes is a logical place to start. It's
a personal action that boosts our prop-
erty value and does something for the
environment at the same time. In ad-
dition to providing benefits ranging
from aesthetics to erosion control, trees
help reduce the energy needed for heat-
ing and cooling and thus the fossil fu-
els burned by power plants. One result
is the production of less carbon diox-
ide, a major greenhouse gas.
When selecting a tree for planting, remember "Buyer beware '
'The Best Way to Plant Trees," adapted from American Forests, American Forestry Association, March/April 1990.
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Here at AFA we take the job of tree planting very seriously. We believe that
major changes are needed in the way people think about trees and plant them. The
American Forestry Association has drawn up new guidelines for how to plant a
tree, and unless you've been reading a lot of research information lately, you will
find many surprises such as don't dig a planting pit and don't add soil amendments
to the planting hole.
We'll admit up front that tree planting is a more involved process than we once
thought. The new information we've developed requires more than just digging a
hole that fits the root ball. It requires more labor, but the result is also very re-
warding. We estimate young trees will grow twice as fast when planted correctly
and will live at least twice as long as trees improperly set out.
Planting a tree is a positive action that is made even more positive when the
species and individual specimen are carefully selected, the tree is strategically located
on the lot, and—what concerns us most in this article—the sapling is properly planted.
Studying the health and survival of community trees, plus working with city
foresters around the world, has led us to make new recommendations on how to
go about planting. The old standards suggested digging a hole six inches wider and
deeper than the root ball. Up until a couple of years ago, the experts also suggested
that community tree planters mix peat moss and other soil amendments with the
soil backfill. None of this is recommended today.
Over the last few years we have been searching for clues to the declining health
of community trees, and we are coming to believe that planting methods are a major
culprit. Some old-timers wrinkle their foreheads and look skeptical when the old
methods are challenged. They can take you out and show you tree after tree that
survived and is doing fine, thank you.
So why do we feel so confident that planting techniques need updating? The
main reason is that home construction has changed greatly since the good old days.
Bigger earth-moving equipment and less hand labor are used in creating today's
housing developments. Because of the heavier construction equipment, the soil in
the average yard is less fertile and more compacted.
Digging a hole in dense, compacted soil and filling the hole with peat moss
and other soil amendments is like creating a pot for the tree. The roots grow outward
in the soil amendments, and the tree does fine until the roots reach the original
soil and the outward growth stops. Instead of spreading into the yard, the roots
encircle the planting pit. The "pot" soon fills with roots, and the health of the
tree declines.
The crown continues to grow, but the roots do not. Once the tree becomes root
bound, its ability to maintain itself during a drought or survive a flood is limited—
leading to decline that is often terminal.
So what do we propose? Plant so that roots have a chance to grow into the sur-
rounding soil and produce healthy, vigorous branches, foliage, and roots. Instead
of a planting hole, what's needed is a large planting area that is wide but not deep,
where the soil is loose and suited for root growth. The larger the area, the better.
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Appendix E: The Best Way to Plant Trees
Planting Tips
After selecting a suitable location, mark out a plant-
ing area that is five times the diameter of the planting
ball. Use a rototiller or shovels to loosen and mix the
soil in this entire area to a depth of about 12 inches.
Organic matter can be added to the loosened soil so
tong as the new material is used uniformly throughout
the area.
In the center of the prepared area, dig a shallow
hole to set the tree, root ball and all. The hole should
allow the root ball to sit on solid ground rather than
loose soil. Once the ball is set in the hole, its upper
surface should be level with the existing soil.
After the tree is properly situated, cut and remove
the rope or wires holding the burlap in place and secur-
ing any part of the tree. Position the tree so that is
perpendicular to the ground, so the main stem will grow
straight up.
Backfill around the root area and gently step the soil
to prevent major air pockets, but it is a mistake to pack
soil too hard. Water can be used instead of your foot to
help the soil settle and prevent overpacking. Rake the
soil even over the entire area and lay mulch on the area
using two to four inches of bark, wood chips, old saw-
dust, pine needles, leaf mold, or the like. Some mulches
decompose quickly and will have to be replenished once
or twice a year. Maintaining the mulch layer carefully
will improve tree growth substantially.
Some planting recommendations suggest mounding
the soil at the outer edge of the planting ring to form a
water-holding berm, close to the tree. The berm will
help hold water, but it may also encourage the root
growth to remain within the berm, close to the tree. So
berms are not recommended here; mulch should hold
the water adequately.
If needed, support the tree with a flexible stake so
that the trunk can sway in the wind. The movement is
necessary for building the trunk's strength. Remove the
stake and rope after one year, since leaving rope around
the tree can kill it.
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We hope to have spurred your interest in planting—especially in doing it right.
Our focus here is planting, but we don't want to leave you without a few words on
selecting a suitable planting location, which is the first step in the whole process.
Paramount in this consideration is energy conservation. Research by Dr. Hashem
Akbari of the Lawrence Berkeley Building Laboratory in Berkeley, California, shows
that energy savings can run as high as 50 percent when vegetation is properly located.
Researchers Gordon Heisler in Pennsylvania and Jack Parker in Florida have
helped identify specific optimum locations. The basic model calls for shade trees
on the south-facing side of a house, with the southeastern and southwestern sides
being the most important locations in terms of summer cooling. The detrimental effects
of winter winds are addressed by planting evergreens (pine, spruce, fir, or hemlock)
on the northeastern section of your lot.
Deciduous trees are the best choice for summer shading since the foliage adds
cooling benefits during the hot months, while the leaf drop in fall allows the sun to
reach the windows of the house and contribute solar heat gain during the winter.
A minimum of three trees are recommended. They should be sited so they can
grow vigorously; allow space for both roots and branches to develop.
Species selection should be geared toward producing medium to large trees for
these strategic spots so that both the roof and the sides of the building receive shade.
As the trees mature, the low winter sun will be able to reach the house from underneath
the branches.
Evergreen windbreaks work best as group plantings containing at least four trees,
but the more the better. Spacing between the trees should be six to 10 feet, which
gives the trees some room to grow but allows branches to meet and form a wind-
break as the trees mature.
As your knowledge of the landscape increases, you will be able to make many
other energy-saving plantings around the home. Trees that shade air conditioners
are most effective at improving the efficiency of the cooling units. Trees and shrubs
can also be located to direct summer breezes through open windows, shade walls,
or create air movement where ventilation is needed.
Although strategic location is the most important consideration, the impact of
the vegetation is also directly related to its overall size and abundance. The effec-
tiveness of the landscaping at moderating the climate will be increased by filling
available space with small, medium, and large plants. Each plant has its niche, so
it is the job of the landscaper to review site conditions and select plants that fit the
local needs.
When it comes to actual selection, don't assume that the cheapest tree is the best
tree. It is usually the worst. One planting recommendation that has remained un-
changed over the years is that a quality tree is the best investment.
First, you need to decide which species is the right one for your spot. Be sure
to get some help here if you don't know. Some trees grow well on wet sites, and
others do better on dry sites. Know the conditions and find out what trees do best
in your area. Matching a tree to a site is a problem that must be addressed locally.
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Appendix E: The Best Way to Plant Trees
To find answers, ask for information at your state forestry office or Cooperative
Extension Service, or go to a local arboretum, garden center, or nursery.
Nurseries offer a tremendous range in quality of trees. Not all the trees are good
ones. Two things must be considered by the buyer. First, is this the right tree for
my site, and second, is it in good condition and ready for transplanting into the cold,
cruel world?
Scientists are working with nurserymen to develop genetically superior trees,
and with each passing year, better specimens will become available. As a buyer,
you need to be assured that the improved genetic line has been passed along to the
young plants. Selecting trees by named varieties or cultivated variety will address
some of these problems.
To determine the health and condition of a tree, eyeball the trunk, branches, and
root ball for signs of damage, and use the guidelines supplied by the American Asso-
ciation of Nurserymen (see below) to determine if the nursery has handled the tree
properly. Nursery growers will refer to their management techniques as cultural practices.
Trimming will give the crown a strong structure and raise the branching up the
trunk. Pruning the branches on the main stem needs to be done carefully. The branches
help the tree put on caliper (diameter) growth, but if they are left on too long, the
wounds from pruning can cause considerable damage to the tree. Roots require pruning
that produces a fibrous and compact system.
By the time a tree leaves the nursery, its shape, size, and direction of growth
have been modified by the nursery's cultural practices to help it survive transplanting
and remain healthy.
If a tree isn't properly root-pruned, for example, most of the roots needed for survival
will be lost during transplanting. The tree may survive, but it will grow slowly and
require a great deal of care. There is a long list of things that need to be done by the
nursery to prepare a tree for street planting. The buyer can learn a lot about the quality
of a tree by asking one question: Is this tree grown to nursery standards? If no one at
the nursery knows what you're talking about, the trees may not be a good choice.
The following is what you should look for when buying a tree. These recom-
mendations are an abbreviated review of the standards published by the American
Association of Nurserymen (1250 I St., NW, Washington, D.C. 20005).
The standard measure for balled-and-burlapped trees is caliper, or the diam-
eter measured six inches above the ground (for trees larger than one half inch and
smaller than four inches in diameter).
A proper relationship of height to caliper assures that the tree's size is in proportion
to the strength of its trunk. The average height of a two-inch-caliper tree is 12 to
14 feet, and the maximum height is 16 feet.
The amount of roots left on the tree is critical to survival. For bare-root trees,
a two-inch-caliper tree should have a minimum root spread of 32 inches. If the tree
has a root ball, the ball must be of a diameter and depth to encompass enough fibrous
roots for full recovery of the plant. The ball diameter for a two-inch tree is 24 inches,
and its depth is about 16 inches.
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If all these directions are followed—nursery standards, careful selection of species,
proper location on your lot, and our new planting recommendations—tiien you'll
have a solid chance of nurturing a healthy tree. Of course, you must water it when
necessary, stand guard against errant vehicles, and—just to cover all bets—talk to
it occasionally. A kind word never hurt anyone.
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Appendix F
Southern California Edison1
Trees and Shrubs
Planting Trees and Shrubs, Step by Step
Trees and shrubs must be planted, watered and cared for properly to ensure they
have a long, healthy life. Plant in fall (preferred) or spring in mild-winter climates; in
spring in cold-winter areas. Follow these important steps.
1. Be sure site is safe for planting, as discussed on page 202. Dig planting hole
twice the width and the same depth as the plant's rootball. If your soil is very
sandy or heavy clay, blend one-third original volume of soil amendment, such
as ground bark or other composted organic material with original soil for backfill.
If your soil is good loam, use as is.
2. Fill planting hole with water to check drainage. After water drains, fill again.
Water should drain in 12 hours or less. If not, select another site.
3. Gently remove plant from container. Free roots from bottom and sides. If rootbound
(a tight mass of roots), use a knife to slice partway up through the rootball,
and spread apart.
4. Place plant in hole, positioning it at original soil level. Fill in around rootball,
firming lightly to remove air pockets. If planting a bareroot plant, follow the
same procedure, but dig hole large enough to accommodate roots. Build cone
of soil at bottom of hole and lay roots over cone. Then add backfill as ex-
plained above.
5. Use soil to build a watering basin around the perimeter of the rootball. Water
slowly to saturate rootball area. Cover area with 2-inch layer of organic mulch
to reduce moisture loss through evaporation.
6. Keep rootball soil moist (not soggy) for the first few weeks. Continue to wa-
ter regularly. Gradually reduce irrigation frequency and increase amount of water
applied each irrigation to encourage deep rooting. After a few months, extend
basin outward several inches to allow for spread of roots.
The excerpts in Appendix F are taken from a brochure distributed by the Southern California Edison
(SCE) utility company, titled "Trees: Saving Energy Naturally," 1991. The information pertains to
planting trees in Southern California. It is provided here mainly as an example of the kind of in-
formation useful to a tree-planting program.
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Figure F-1.
Proper support Trees need to have stakes for sup-
port before their root systems gain strength.
Staking
Drive two sturdy stakes, tall enough to
support the trunk, about two feet deep into
soil outside of rootball. Place on opposite
sides of trunk. Tie trunk loosely to stakes
—enough for support but not so tight that
the tree cannot move on its own to gain
strength. Prune only lightly, removing bro-
ken, crossing branches.
Ways to Save Water
With roughly half of residential water
use going to home landscapes, it pays to
select low-water-use plants. Choose plants
that are naturally adapted to grow with
minimum water. For example, water con-
sumption for a mulberry (Morus alba), a
popular shade tree, requires almost three
times more water than the similar African
sumac (Rhus lancea).
Most of the trees and shrubs described
in this booklet are low water-use plants. Some additional ways to save water include:
• Water in early morning hours when it's cool and the winds are calm to reduce
evaporation loss.
• Water slowly and for long periods to encourage deep rooting. Plants will have
greater reservoirs of soil area for drawing moisture and anchoring themselves.
• Learn your soil type—sandy, clay or loam—and adjust watering practices to apply
just enough water for plant growth. Sandy soil drains fast, clay drains slow. Loam
is somewhere between.
• Add amendments to soil so moisture is retained in the root zone longer. This is
not always practical with trees and shrubs, but works well for flower and veg-
etable gardens.
• Water plants at the drip line—an imaginary line where rain-water would fall from
leaves to the ground. This is the area where feeder roots are most concentrated.
• Use a moisture-conserving mulch such as ground bark or other composted or-
ganic material over the root area to cover soil and reduce evaporation.
• Install a drip irrigation system to water plants slowly and efficiently.
Plant Care and Your Safety
Always stay far away from power lines. Be sure to remember this when pruning
trees or shrubs. And, never use an aluminum ladder. Also, be careful with tree-trim-
ming and fruit-harvesting equipment around power lines. If you are holding a metal
pole of any kind and it contact a power line, you could be killed. Also be aware that
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Appendix F: Trees and Shrubs
water is a good conductor of electricity. Never use electric tools such as hedge trimmers or electric lawnmowers
if your hands or feet are wet, or if you're standing in water or on damp ground. Keep electric tools and cords
away from damp grass and shrubs, and never use electric tools near a swimming pool.
Climate Zones
C = Coastal, IV = Inland Valleys, LD = Low Deserts, HD = High Deserts, M = Mountains. All climate
zones are general, and can vary considerably. Use the recommendations in the following diagrams (Figure
F-2) only as a guide. For best results, check locally to see if plants are adapted to your area.
Figure F-2.
Acacia
Acacia species
Acacia represents hundreds of species of
evergreen trees and shrubs. Leaves are
delicate and lacy. A. abyssinlca, Abyssin-
ian acacia, grows up to 30 feet high with a
wide-spreading canopy. A.farnesiana, (A.
smallii), sweet acacia, grows to 20 feet.
Leaves are green, fern-like. Low water
use. C, IV, LD.
African sumac
Rhus lancea
Evergreen grows 20 to 25 feet high, spreading
even wider. Trees gradually take on a broad,
dome shape. Leaves are narrow, glossy,
medium green. Creates dense shade. Low
water use. C, IV, LD.
F. oxycarpa 'Raywood,' deciduous to 35
feet. Fast growth. F. uhdei, Shamel ash,
evergreen to deciduous to 60 feet. Do not
plant near power lines. 'Majestic Beauty'
is an improved variety. Narrow, upright
form spreads with age. Leaves are dark
green in leaflets. F. velulina 'Rio Grande'
(fantex ash) is drought and heat tolerant.
Low water use. C, IV, LD, HD.
Australian willow
Geijera
parviflora
Evergreen, grows to 30 feet; 20-foot canopy.
Upright form. Graceful, willowy presence.
Leaves are medium green, 3 to 6 inches
long. Low water use. C, IV, LD, HD.
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Bottle tree
Brachychiton populneus
Evergreen, fast growing to. 50 feet, 30-
foot canopy. Pyramidal shape. L'eaves are
shiny dark green. Excellent in hot areas.
Often used as a windbreak. Low water
use. C, IV, LD.
California pepper
Brazilian pepper
Schinus species
S. molle, California pepper, evergreen grows
fast to 40 feet high, with wide canopy.
Branches droop willow-like, covered with
bright green leaves. S. terebinthifolius,
Brazilian pepper, evergreen, grows to 30
feet. Growth is more rounded. Leaves are
glossy dark green. Low water use. C, IV,
LD.
Carrot wood
Cupaniopsis
anacardiopsis
Chinese pistache
Pistacia chinensis
Evergreen to 40 feet high, spreading 20 to
30 feet. Attractive, dark green, leathery
leaves. Even but not dense shade. Fruit
occasionally messy. C, IV.
Deciduous, grows up to 50 feet high and
spreads as wide. Long, bright green leaf-
lets allow filtered shade. Leaves are pink-
ish when new; brilliant yellow, orange and
red in fall. Low water use. IV, LD, HD.
Cottonwood, Poplar
Populus species
Trees for fast shade. P. alba, white poplar,
deciduous to 60 feet high. Leaves are me-
dium green, light green underneath. 'Bolleana'
(also 'Pyramidalis') is more upright. P.
fremontii, Fremont cottonwood, decidu-
ous grows to 90 feet. Glossy green leaves
turn yellow in fall. Caution: Usually needs
more water and has invasive roots. IV,
HD, M.
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Appendix F: Trees and Shrubs
Crape myrtle
Lagerstroemia indica
Deciduous shrub or small tree, vase-shaped
to 30 feet. Often with multiple trunks. Pro-
fuse flowers in summer. 'Indian Tribe' group
is disease resistant. Low water use. IV, LD,
HD.
Desert willow
Chilopsis
linearis
Eucalyptus
Eucalyptus species
Deciduous, to 25 feet, spreading to 25 feet.
Leaves are green and willow-like on twisted
branches. Orchid-like flowers are snowy white
to lavender and bloom in spring and sum-
mer. Low water use. IV, LD, HD.
Large group of evergreen trees and shrubs.
Fast-growing and accepting of difficult con-
ditions. Some get quite large; can be messy.
Do not plant near power lines. E. citriodora,
lemon-scented gum, grows to 75 feet, spreading
to 25 feet. E. polyanthemos, silver dollar
eucalyptus, to 30 to 60 feet. Leaves are sil-
very gray-green, round like silver dollars,
becoming lance-shaped with age. Low wa-
ter use. C, IV, LD.
Floss silk tree
Chorisia
speciosa
Deciduous, but for a short time. Grows to 60
feet; pyramidal form. Produces profuse amounts
of pink flowers in fall. Trunks are studded
with spines. C, IV.
Flowering plum
Flowering cherry
Prunus
species
P. carolinana, cherry laurel, evergreen large
shrub or small tree 20 to 40 feet high. Pyra-
midal form. Shiny, dark green leaves. White
flowers in clusters in spring, blue berries in
fall. Many varieties of P. cerasifera, cherry
plum, are available. 'Atropurpurea,' purple-
leaf plum, is one of the most common. De-
ciduous to 30 feet high. Highly ornamental
dark purple leaves and white flowers. Cherry
laurel: Low water use. C, IV, LD, HD. Cherry
plum: IV, LD, HD.
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Golden-rain tree
Koelreuteria paniculata
Deciduous to 20 to 35 feet. Open branch-
ing growth habit. Leaves are soft, medium
green. Flowers are striking yellow and
bloom in late spring. Fast-growing. Can
be invasive when it reseeds. K bipinnata,
Chinese flame tree, is deciduous to 40
feet. Low water use. C, IV, LD, HD.
Hackberry
Celtis occidentalis
Deciduous to 50 feet and almost as wide.
Oval leaves are 2 to 5 inches long. Tough
tree. All areas where cold-hardy. Low water
use.
Honey locust
Gleditsia triacanthos
inermis
Deciduous to 30 to 55; wide canopy. Leaves
are green to dark green, delicate and lacy.
Excellent lawn tree. Likes heat. Many im-
proved varieties with colorful leaves. IV,
LD, HD.
Jacaranda
Jacaranda mimosifolia
Deciduous to semi-evergreen, to 40 feet,
spreading 30-foot canopy. Oval irregular
form. Leaves are fern-like. Lavender-blue
blossoms in late spring to early summer.
C, IV, LD.
Locust
Robinia species
R. ambigua 'Idahoensis' ('Idaho'), decidu-
ous, grows to 40 feet high, upright habit.
Leaves in leaflets are medium green, up to
12 inches long. Clusters of deep pink flowers
in late spring. R. pseudoacacia, black lo-
cust, deciduous and fast-growing to 40 to
75 feet high. All areas where cold-hardy.
Low water use.
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Appendix F: Trees and Shrubs
Mesquite
Prosopis species
Deciduous to evergreen, ranging in size
from small native shrubs to wide-crowned
trees to 40 feet high and as wide. P. alba,
Argentine mesquite, has blue-green leaves.
P. chilensis, Chilean mesquite, has fern-
like foliage and dark trunk. Also look for
hybrid mesquites. Low water use. IV, LD,
HD.
Oak
Quercus species
Quality trees for the West. Some of the
best include: Q. agrifolia, coast live oak,
evergreen, grows to 30 to 60 feet high.
Crown becomes dome-shaped with age.
Leaves are shiny green and holly-like. Q.
lobata, valley oak, deciduous, grows to 60
to 75 feet high, spreading 50 to 80 feet
wide. Low water use. Generally adapted.
Check locally.
Olive
Olea europaea
Ornamental pear
Pyrus species
Evergreen 20 to 30 feet high, often with
multiple trunks. Wide-spreading canopy.
Leaves are leathery, silvery gray-green.
Dark blue-black fruit in fall can be a messy
problem. Look for "fruitless" varieties;
planting restrictions in some communi-
ties. Low water use. C, IV, LD, HD.
P. calleryana, callery pear, deciduous, grows
to 25 to 40 feet. 'Aristocrat' is pyramidal
in form. Bright green leaves produce spec-
tacular fall color. P. kawakamii, evergreen
pear, grows to 30 feet. Leaves are shiny,
light green with wavy edges. Flowers are
white and profuse in early spring. IV, LD,
HD.
Palo verde
Cercidium species
C.floridum, blue palo verde, deciduous up
to 30 feet and about as wide; dense, low-
spreading branches. Spring flowers are golden
yellow. Leaves, bark and trunk are green.
Also consider the similar Parkinsonia species,
Mexican palo verde. Low water use. IV,
LD, HD.
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Pine
Pinus species
Large group of evergreens. Look for P.
brutia eldarica, Eldarica.pine, very fast
growth to 50 feet high. P. halepensis, Alleppo
pine, is similar to eldarica. Not quite as
fast growth, not as symmetrical. P. pinea,
Italian stone pine, grows 40 to 80 feet. P.
thunbergiana, Japanese black pine, fast
growth to 30 feet, sometimes higher. Ad-
aptation depends on species and cold tem-
peratures in your area. Check locally.
Silk tree
Albizia julibrissin
Sycamore
Platanus species
Deciduous, grows slowly to 30 feet or
higher, with a broad canopy. Leaves have
fern-like texture; pink, pin-cushion flow-
ers in summer. All areas where cold-hardy.
P.x acerifolia, London plane tree, decidu-
ous and fast-growing to 60 feet high with
50-foot canopy. Large, coarse bright green
lobed leaves. P. racemosa, California sy-
camore, grows fast to 50 to 100 feet, spreading
wide. Leaves are dark green, bark is at-
tractive mottled tan. Tolerates heat and
wind. All areas where cold-hardy.
Bottlebrush
Callistemon species
C'. citrinus, lemon bottlebrush, evergreen
shrub or small tree 20 to 25 feet. Narrow,
round-headed form. Cylindrical, 'bottle-
brush' flowers are bright red. C. viminalis,
weeping bottlebrush, is slightly taller with
drooping branches. Low water use. C, IV,
LD.
Hopbush
Dodonaea viscosa
Evergreen, grows to 10 feet high and about
5 feet wide. Leaves are green and cover
plants densely. Fast rugged growth. 'Purpurea',
with purplish leaves, is more refined. Low
water use. C, IV, LD.
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Appendix F: Trees and Shrubs
Juniper
Juniperus species
Oleander
Nerium oleander
Photmia
Photinia
species
One of the most dependable and adaptable
group needled evergreens for the West.
Hundreds of cultivated varieties to choose
from. J. chinesis and J. scopulorum are
common upright forms. Check individual
species for mature size. All areas where
cold-hardy. Low water use.
Popular evergreen shrubs reaching to 12
feet (or higher), and almost as wide. Long,
narrow, dark green leaves on upright stems.
Flowers in white, red and pink and are
profuse in spring scattered through sum-
mer. Plant parts are poisonous. Low water
use. IV, LD, HD.
Privet
Ligustrum species
P.x fraseri, red tip photinia, evergreen,
grows to 12 feet high. Lush, bronze-red
new growth in spring turns a rich, shiny
green. White flowers in flat clusters in
spring. P. serrulata, Chinese photinia, is
similar, slightly smaller and more open
growth. IV, LD, HD.
L. japonicum, Japanese privet, evergreen,
grows to 15 feet or higher to make an
outstanding screen. Glossy, dark green leaves
with whitish undersides. Berries can be
messy. L. lucidum, Chinese privet, ever-
green shrub or small tree to 30 feet. All
areas where cold-hardy. Low water use.
Xylosma
Xylosma congestum
Evergreen shrub or small tree grows slowly
to 15 feet, spreading almost as wide. Leaves
are glossy, yellow-green—giving the plant
a lush appearance. Excellent as a spread-
ing shrub or clipped hedge. Low water
use. C, IV, LD, HD.
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SEASONAL SUN ANGLES AND DAY LENGTH
Noon, December 22 (Winter Solstice)
Sun angle 32° in sky.
Noon, June 22 (Summer Solstice)
Sun angle 79' in sky.
SEASONAL SHADOW LENGTHS • NOON • 9 AM & 3 PM
June 22 (Summer Solstice)* December 22 (Winter Solstice)'*
8 AM & 4 PM * Summer shadows fall in west-southwest direction in
morning, in east-southeast direction in afternoon
** Winter shadows fall in northwest direction m morn-
ing, in northeast direction m afternoon Shadows at
noon go m the northerly direction all year long.
625'
500'
375'
4' 17' 43'
31' 61'
Figure F-3.
Sun angles and shadow lengths: These diagrams show the paths of the sun during winter and summer, and the resulting tree shadows
for various times of the day Note: These diagrams all pertain to Southern California conditions.
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Appendix G
Pasadena Water and Power Department'
Sample Tree Planting
Incentive Program
Planting trees is an effective way to save energy and improve the environment.
A tree planted on the west and/or south side of your home cools your home
naturally, thus decreasing the necessity for air conditioning. Energy saved from
planting trees also helps to diminish peak power demand, thereby reducing the need
for expensive new power plants. Additionally, trees help to improve our local air
quality by filtering dirt and pollutants from the air and lessening the global greenhouse
effect. You will receive, for each tree planted, either a $10 cash rebate (check) or
an energy-saving compact fluorescent light bulb with a retail value of $15. Customers
can receive rebates for up to three trees. Program is subject to availability of funds.
Tree Selection
There are many beautiful deciduous and evergreen trees to choose from. Deciduous
trees drop their leaves each winter allowing sun to penetrate through to warm your
house. Evergreen trees keep their leaves year-round. Evergreens should not be located
on the southwest, south or east exposures of your home if you want to take advantage
of the winter sun to warm your home. The trees on this chart (See Figure G-l) are
only a few examples of the types that are suitable for the Pasadena area. For a more
complete list of low water use trees and planting and maintenance guidelines, contact
your local nursery or call (818) 792-POWER.
The main objective of shading your home with trees is to shield the roof and walls
from hot summer sun. The more area you shade, the cooler your home will be. Larger
trees which shade a sizeable area with less dense coverage are preferable to smaller
compact trees which shade a modest area with dense coverage. Consult your local
nurseryman or landscape professional with specific questions about the characteristics
'The information and table in Appendix G are taken from a brochure distributed by the Pasadena Water
and Power Department, titled "Tree Planting Incentive Program," 1990.
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and special needs of the trees you wish to plant. The Sunset Western Garden Book
(1987) is one of the many publications which can provide you with additional in-
formation about the tree you select.
Tree Selection Chart
Figure G-t.
Botanic Name
Common Name
HGT/WTH
Type
Comments
Acacia bailyana
Albizia juhbrissin
Arbutus unedo
Brachychiton populneus
Cretis occidentahs
Ginkgo biloba (males)
Koelreuteria bipinnata
Lagerstroemia indica
Platanus acerfolia
Ouercus agrifolia
fernleaf wattle
mimosa tree
strawberry tree
bottle tree
western redbud
maidenhair tree
Chinese flame tree
crape myrtle
London plane tree
coast live oak
20720'
30735'
25725'
40725'
20720'
50725'
50735'
25725'
50730'
40740'
deciduous
deciduous
evergreen
evergreen
deciduous
deciduous
deciduous
deciduous
deciduous
evergreen
grey foliage
pink flowers
red berries
white flowers
Calif, native
fan shape leaves
orange seed pods
showy flowers
fall color
Calif, native
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Appendix H
American Forestry Association1
Planting New Life in the City
Down the Street
Trees are as much a part of our street environment as are fire hydrants, light poles,
and sidewalks. They help to define rights-of-way, as well as the age and spirit
of a community. Trees are the first thing we see as we enter a neighborhood—they
form our first and lasting impression of a place. They also provide significant eco-
logical and economic benefits that far outweigh the cost of planting and caring
for them.
Planting trees along a street can be a difficult task. Streets are cluttered and
compacted environments for a growing tree. In addition, there are legal, political,
technical, and economic issues to be considered when planting on public property.
Tree selection and planting methods essentially determine how long a tree will
live. A species that grows very tall and conflicts with utility lines will suffer from
heavy pruning to keep the lines unobstructed. Matching the right species and variety
of tree to the site will extend its ability to survive.
Perhaps an even bigger concern is underground. Trees like the American sycamore
are too big and muscular for sidewalk pits or small planting strips. Final decisions
on tree selection should be based on the expected mature size of the tree. The more
confined the planting area, the more knowledgeable the planter must be.
Our first street-side planting recommendation is for planting in the street lawn
(or treelawn), between the sidewalk and curb. Our planting model is a five-foot-wide
grass strip that extends along the full length of the street. The first step in this kind
of planting is to loosen soil with a rototiller or shovel over an area including the
width of the treelawn and eight feet in length, just as you would if you were planting
around your home.
'Excerpted from Urban Forests, April/May 1991, vol. 11, no. 2
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Preparing a treelawn for planting is like yard planting, but slightly more restricted.
The prepared planting area will be a rectangle instead of a circle, and it will not be
quite as large. Mark out a five-foot by eight-foot rectangle, and loosen the soil to
the depth of the rootball. The ideal planting area looks like the bottom of a bowl (unless
drainage is a problem—see discussion below) with the center the same depth as the
ball and the outer edges only a few inches deep. Now simply follow the last five points
in the section on planting trees in yards (See Appendix E).
Unfortunately, many urban streets do not have a treelawn. Instead, they have a
wide sidewalk and a small pit of soil every 20 or 30 feet. Because of space, restrictions,
a sidewalk pit presents probably the greatest treeplanting challenge. Though there
is wide agreement that new, radical approaches to planting trees in the city are needed,
the sad reality is that in many cities over-restrictive sidewalk pits, or "concrete coffins,"
are the only street spaces available for tree planting.
As the trees in these existing sidewalk pits die, cities don't have the resources
to rebuild street infrastructures to provide adequate root space. There are, however,
a few things we can do to increase the life spans of trees planted in these places.
First, attempt to determine why a tree died before planting a new one. Poor drainage
is a common cause, so determine if the pit will drain. Here's a simple test: Dig a small
hole (10 inches in diameter and 12 inches deep) in the pit and fill it with water. After
it drains, fill it again and see how long it takes for the water to soak into the ground.
One inch per hour is the minimum drainage needed to support tree growth.
Next, measure the size of the pit. It should be at least 30 square feet, with four feet being
the minimum width. If the pit is not six feet by five feet or eight feet by four feet, find out
if there is an opportunity to expand the root space under the sidewalk. Stormdrain inlets,
gardens, or adjacent lawn space within 10 feet of the pit may enhance a tree's available root
space. Broken pavement is often an indication of a tree's success in reaching more space.
Another possible remedy is to enlarge the pit (the larger the site, the larger the
tree will grow). After the appropriate permission has been obtained, use a cement
cutter to cut the pavement and remove the surface and sub-base. Excavate all of the
soil in the resulting tree pit to a depth of 24 to 30 inches. In soil of moderate to poor
drainage, install an aeration ring and a drain sump.
To keep the rootball from sinking into the fresh backfill (a major cause of decline
in newly planted trees), construct a compacted mound under the rootball and set the
rootball in the pit so that its top is three inches above the adjacent sidewalk. Fill in
the pit with the same soil that was taken out (do not add soil amendments except in
very sandy soils). Finally, cover the pit with two to four inches of bark mulch.
In areas with high pedestrian traffic, brick or stone sand-set pavers can be added
to the surface of the pit. Set the rootball and the soil volume lower as required. Adding
these pavers, however, will have a negative impact on a tree's potential growth.
Roots and Sidewalks
If large trees are to mature successfully in an urban environment, they will inevita-
bly have to establish roots outside the original planting hole. Root expansion is restricted
by the sidewalk on one side and the curb and street on the other. The most likely root expansion
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Appendix H: Planting New Life in the City Down the Street
is parallel to the street, and the next most likely is under the sidewalk. Though root growth
under streets is unusual, root expansion under sidewalks is both a common problem for
public-works departments and opportunity to improve tree health in the future.
When tree roots hit the compacted soil under pavement, they tend to grow in a
thin, shallow soil zone along the underside of the pavement where there is more oxygen
and moisture. Once they grow beyond the sidewalk and into more soil, a new system
of fine roots takes advantage of available water and nutrients. This new growth changes
the function of the roots under the sidewalk from absorption to transport. As the flow
of water and nutrients increases, the diameter of the transport roots also increases,
and as the roots enlarge, they can lift and damage the pavement.
Attempting to stop sidewalk damage by cutting tree roots and replacing sidewalks
is expensive and can be fatal to the tree. Sidewalk and root conflicts can be solved
only when urban foresters and city engineers work together to address the needs of
both the trees and the pavement. Discussion should take place when sidewalks are
being installed or repaired, and when new trees are plated. The best solutions are
found when new trees and new pavement are installed at the same time. Select a tree
for the largest available planting space, and provide adequate space for root growth
such as aerated rooting channels under the pavement.
Preventing a conflict where trees and sidewalks already exist is the most difficult
conflict to resolve. Creating more space around the tree is the best answer. This can involve
cutting away part of the sidewalk or diverting the walk to allow more space for tree growth.
Even when more space is created, a tree expert should be consulted to prevent serious
damage to roots.
When new trees are planted where sidewalks already exist, various methods can be
employed to reduce conflicts. Various types of root barriers can be installed to physi-
cally deflect roots. Though the barriers deter root damage to sidewalks, they also limit
tree growth. Barriers that encircle the tree's roots are the most restrictive to root development.
This kind of barrier is being used with some success in parts of the country where soils
are well aerated and not wet. Any use of these devices east of the Mississippi River is
questionable because soil density and moisture levels are higher there.
The most promising root barrier is one that deflects the roots only where sidewalk
and street protection is needed. Barriers can be placed next to the edge of the pavement,
for eight feet on either side of the tree, for example, and provide protection for the
sidewalk while allowing more root space than encircling root collars will.
Even more creative elements are now being added to root-deflector systems. One
new product acts as a barrier and a conductor, not only deflecting roots but also
providing a pathway for them to follow. The pathway attempts to provide improved
soil moisture and aeration for root development.
Open Spaces
Open spaces, greenways, and parks offer some of the best opportunities for tree planting
because newly planted trees will have adequate space to grow. In addition, many trees
per acre can be planted in parks, with less need to ensure the survival of each tree. Open-
space planting offers a good opportunity to plant smaller trees, and more of them.
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Small-tree planting may prove to be the salvation of our inner-city greenways,
riparian corridors, highways, and boulevard medians. Planting bare-root .seedlings,
whips, and saplings is a citizen-sized effort that encourages volunteer participation.
But keeping these young trees alive requires forethought—careful species selection
and handling, and impeccable timing for the planting event. The most important factor
is the drive of the citizens who plant them. Concerned citizens must be willing to
follow through by watering and weeding during the first three years.
Whether the purpose of a planting event is soil conservation, beautification, or
windbreaks, the precautions are the same. The gathering of trees and people should
occur on the same day. The planting site should be cleared of debris—trash and
underbrush removed, and the grass cut. Individual planting holes should be clearly
marked for the volunteers.
Perhaps the biggest problem with planting small trees in open areas is damage
from people. Small trees often go unnoticed by groundskeepers and become vic-
tims of lawn mowers, or are damaged by visitors or vandals. A relatively new product
that is helping to establish small trees is called a tree shelter. It is a biodegradable
polypropylene tube fits around the tree, supplying both protection and improved
growing conditions.
To plant with a shelter, clear an area two feet in diameter—removing all grass—
and cultivate the soil to the depth of the root mass (equivalent to the rootball on a
larger tree). Plant the tree in the center of the area with the roots level or slightly
higher than the surrounding soil. Install the tree shelter, and water the new tree slowly
and thoroughly.
Many of the available planting areas in a city strain a tree's ability to adapt and
survive. The average tree planted in a downtown sidewalk of a big city, for example,
lives only seven to 10 years. Finding a space will allow a tree to live a long time is
one of urban forestry's great challenges.
If your community is going to plant trees this year, scout out the best locations.
They are generally the largest areas of soil (the most important factor) with the fewest
above-ground restrictions. The soil in the larger planting areas can be worked to
dramatically improve the life of the tree.
During your search for planting locations, you will undoubtedly find some that
are unsuitable because of their soil content. Therefore, work with planners, engineers,
and community foresters (if available) between planting seasons to improve quality
of these sites so that you can plant in them next year without undue strain on the tree.
One of the environmental goals for the 1990s should be to plant more trees and
to take responsibility for their survival. You can take an important step toward en-
suring a tree's survival by planting it the new AFA way—this is the best informa-
tion we have to date. Please use it and pass it on to your friends, neighbors, and
community leaders.
They say it is difficult to get experts to agree on anything. But in writing this
article, our experts found many areas of agreement In fact, on this final point there
was absolute agreement: Planting a tree is a simple act, but it takes three long years
to establish a tree. Planting it right is the first step!
216
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Appendix H: Planting New Life in the City Down the Street
A Little Tree Glossary
Backfill: To return soil to a planting area from which it was originally taken.
Bare-root seedling: A tree ready for transplanting that has had the soil
around its roots removed.
Brick or stone sand-set paver: Brick or stone set in sand and placed
around a tree to allow water infiltration and give protection
from pedestrians.
Drain sump: A pipe that helps to drain excess water from a planting hole.
Greenway: A linear open space that stretches into or around cities, usually
containing trees, shrubs, and grassy areas.
Riparian Corridor: The green area along a waterway such as a river,
stream, or lake.
Rootball: The clump of soil containing the roots of a tree.
Rototiller: A power-driven machine that uses metal teeth to chop up and
mix soil.
Sapling: A young tree that measures two to four inches in diameter.
Sidewalk pit: The small patches of soil found amid the sidewalks of the
most urbanized sections of a city. The pits are designed as a sort
of "street planter" for trees or other greenery.
Treelawn: The grassy area between street and sidewalk.
Well-aerated soil: Soil that has been loosened, breaking up compaction
and adding air space.
Well-developed soil: Undisturbed soil with a many-layered profile, rich
in organic matter at the top and minerals near the bottom.
Whip: A young tree; often a bud graft on an established root system that
has developed a main stem but very few branches.
<rU S GOVERNMENT PRINTING OFFICE 1992-309-598
217
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Abstract
Summer temperatures in urban areas are now typically 2 to 8°F higher than in their rural surroundings,
due to a phenomenon known as the "heat island effect." Research shows that increases in electricity
demand, smog levels, and human discomfort are probably linked to this phenomenon. Cooling Our Communities:
A Guidebook on Tree Planting and Light-Colored Surfacing, produced by the U.S. Environmental Protection
Agency, is the first action-oriented guide that addresses the causes, magnitude, and impacts of increased
urban warming, suggests strategies which can be taken to combat the problem, and estimates the level of
possible benefits that may be achieved.
Two of the most cost-effective methods of reducing heat islands are strategic landscaping and light-
colored surfacing. Strategic landscaping refers to planting trees and shrubs around buildings and throughout
communities to provide maximum shade and wind benefits. Light-colored surfacing means changing dark-
colored surfaces to ones which effectively reflect—rather than absorb—solar energy. The guidebook shows
that well-placed vegetation around residences and small commercial buildings can reduce energy consumption,
typically by 15 to 35 percent. Savings from lightening surface colors may be as high or greater, but are
still being measured. If widespread planting and lightening occurs, it could also help lower summer
temperatures and reduce the production of smog.
Cooling Our Communities is a compilation of the most current scientific research that is underway
to understand the effects of urban heat islands. It provides citizens with practical recommendations for
implementing mitigation strategies in their communities, and contains lessons learned from successful
tree planting programs. The publication has been developed for the benefit of lay readers, but also includes
several technical appendices to assist those seeking more specific information.
To order a copy of Cooling Our Communities: A Guidebook on Tree Planting and Light-Colored Sur-
facing, indicate stock number 055-000-00371-8 and send $13 for each copy in a check made out to the
Superintendent of Documents or provide your VISA or MasterCard number and expiration date, and send
it to New Orders, Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15220-7954. Or FAX
your credit card order using 202-512-2250.
Superintendent of Documents Publications Order Form
CD YES, please send me copies of COOLING OUR COMMUNITIES: A GUIDEBOOK TO TREE PLANTING
AND LIGHT-COLORED SURFACING, S/N 055-000-00371-8 at $13.00 ea.
The total cost of my order is $ . International customers please add 25%. Price includes regular domestic postage
and handling and is subject to change.
May we make your name/address available to other mailers? Q YES Q NO
Customer's Name and Address
Please Choose Method of Payment:
Q Check Payable to the Superintendent of Documents
Q VISA or MasterCard Account
I I I I IT
(Credit card expiration date)
Zip
(Authorizing Signature) 1/92
Mail To: Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250-7954
image:
*tiiTo"9 °°d" Superintendent of Documents Publications Order Form
O YES, please send me copies of COOLING OUR COMMUNITIES: A GUIDEBOOK TO TREE PLANTING
AND LIGHT-COLORED SURFACING, S/N 055-000-00371-8 at $13.00 ea.
The total cost of my order is $ . International customers please add 25%. Price includes regular domestic postage
and handling and is subject to change.
May we make your name/address available to other mailers? Q YES Q NO
Customer's Name and Address
Zip
Please Choose Method of Payment:
Q Check Payable to the Superintendent of Documents
Q VISA or MasterCard Account
i i I I I I i i i i i i i i rr
I | I | I (Credit card expiration date)
(Authorizing Signature)
Mail To: Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250-7954
1/92
Order Processing Code:
*6170
Superintendent of Documents Publications Order Form
I I YES, please send me copies of COOLING OUR COMMUNITIES: A GUIDEBOOK TO TREE PLANTING
AND LIGHT-COLORED SURFACING, S/N 055-000-00371-8 at $13.00 ea.
The total cost of my order is $ . International customers please add 25%. Price includes regular domestic postage
and handling and is subject to change.
May we make your name/address available lo other mailers? Q YES Q NO
Please Choose Method of Payment:
Q Check Payable to the Superintendent of Documents
Q VISA or MasterCard Account
Customer's Name and Address
Zip
L
11
(Credit card expiration date)
(Authorizing Signature)
Mail To: Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250-7954
1/92
Order Processing Code:
*6170
Superintendent of Documents Publications Order Form
LJ YES, please send me copies of COOLING OUR COMMUNITIES: A GUIDEBOOK TO TREE PLANTING
AND LIGHT-COLORED SURFACING, S/N 055-000-00371-8 at $13.00 ea.
The total cost of my order is $ . International customers please add 25%. Price includes regular domestic postage
and handling and is subject to change.
May we make your name/address available (o other mailers? Q YES Q NO
Please Choose Method of Payment:
Q Check Payable to the Superintendent of Documents
Q VISA or MasterCard Account
(Credit card expiration date)
Customer's Name and Address
Zip
(Authorizing Signature)
Mail To: Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250-7954
1/92
image:
Summer temperatures in urban areas are now typically 2 to 8°F higher than in their rural surroundings,
due to a phenomenon known as the "heat island effect." Cooling our Communities: A Guidebook on
Tree Planting and Light-Colored Surfacing, produced by the U.S. Environmental Protection Agency, is the
first action-oriented guide that addresses the causes, magnitude, and impacts of increases in urban
warming, suggests strategies which can be taken to combat the problem, and estimates the level of possible
environmental and economic benefits.
Two of the most cost-effective methods of reducing heat islands are strategic landscaping and light-
colored surfacing. Strategic landscaping refers to planting trees and shrubs around buildings and
throughout communities to provide maximum shade and wind effects. Light-colored surfacing means
changing dark-colored surfaces to ones which effectively reflect—rather than absorb—solar energy.
Cooling Our Communities provides citizens with practical recommendations for implementing these
mitigation strategies in their communities. The guidebook was developed for the benefit of lay readers,
but also includes several technical appendices to assist those seeking more specific information.
To order your copy, simply fill out the front of this card and mail it to the Government Printing Office
with your payment.
Summer temperatures in urban areas are now typically 2 to 8°F higher than in their rural surroundings,
due to a phenomenon known as the "heat island effect." Cooling our Communities: A Guidebook on
Tree Planting and Light-Colored Surfacing, produced by the U.S. Environmental Protection Agency, is the
first action-oriented guide that addresses the causes, magnitude, and impacts of increases in urban
warming, suggests strategies which can be taken to combat the problem, and estimates the level of possible
environmental and economic benefits.
Two of the most cost-effective methods of reducing heat islands are strategic landscaping and light-
colored surfacing. Strategic landscaping refers to planting trees and shrubs around buildings and
throughout communities to provide maximum shade and wind effects. Light-colored surfacing means
changing dark-colored surfaces to ones which effectively reflect—rather than absorb—solar energy.
Cooling Our Communities provides citizens with practical recommendations for implementing these
mitigation strategies in their communities. The guidebook was developed for the benefit of lay readers,
but also includes several technical appendices to assist those seeking more specific information.
To order your copy, simply fill out the front of this card and mail it to the Government Printing Office
with your payment.
Summer temperatures in urban areas are now typically 2 to 8°F higher than in their rural surroundings,
due to a phenomenon known as the "heat island effect." Cooling our Communities: A Guidebook on
Tree Planting and Light-Colored Surfacing, produced by the U.S. Environmental Protection Agency, is the
first action-oriented guide that addresses the causes, magnitude, and impacts of increases in urban
warming, suggests strategies which can be taken to combat the problem, and estimates the level of possible
environmental and economic benefits.
Two of the most cost-effective methods of reducing heat islands are strategic landscaping and light-
colored surfacing. Strategic landscaping refers to planting trees and shrubs around buildings and
throughout communities to provide maximum shade and wind effects. Light-colored surfacing means
changing dark-colored surfaces to ones which effectively reflect—rather than absorb—solar energy.
Cooling Our Communities provides citizens with practical recommendations for implementing these
mitigation strategies in their communities. The guidebook was developed for the benefit of lay readers,
but also includes several technical appendices to assist those seeking more specific information.
To order your copy, simply fill out the front of this card and mail it to the Government Printing Office
with your payment.
image:
