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Reducing Urban Heat Islands
Compendium of Strategies
Trees and Vegetation
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Acknowledgements
Reducing Urban Heat Islands: Compendiu m of Strategies describes the
causes and impacts of summertime urban heat islands and promotes
strategies for lowering temperatures in U.S. communities. This compendium
was developed by the Climate Protection Partnership Division in the U.S.
Environmental Protection Agency's Office of Atmospheric Programs. Eva
Wong managed its overall development. Kathleen Hogan, Julie Rosenberg,
and Andrea Denny provided editorial support. Numerous EPA staff in
offices throughout the Agency contributed content and provided reviews.
Subject area experts from other organizations around the United States and
Canada also committed their time to provide technical feedback.
Under contracts 68-W-02-029 and EP-C-06-003, Perrin Quarles Associates,
Inc. provided technical and administrative support for the entire
compendium, and Eastern Research Group, Inc. provided graphics and
production services.
PositvEnergy provided support in preparing the Trees and Vegetation, Cool
Roofs, and UHI Activities chapters under contract PO #2W-036 l-SATX.
Experts who helped shape this chapter include:
Ryan Bell, David Cole, Ben DeAngelo, Lynn Desaultes, Ed Dickerhoff, Maury
Estes, Gordon Heisler, David Hitchcock, Kim Klunich, Cheryl Kollin, Megan
Lewis, Julie Magee, Greg McPherson, Dave Nowak, Philip Rodbell, Joyce
Rosenthal, Misha Sarkovich, Kathy Wolf, Jim Yarbrough, and Barry Zalph.
Suggested Citation: U.S. Environmental Protection Agency. 2008. "Trees and
Vegetation." In: Reducing Urban Heat Islands: Compendium of Strategies.
Draft, https://www.epa.gov/heat-islands/heat-island-compendium.
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Contents
Trees and Vegetation 1
1. How It Works 2
2. Using Trees and Vegetation in the Urban Landscape 3
3. Benefits and Costs 5
3.1 Benefits 5
3.2 Potential Adverse Impacts 9
3.3 Costs 11
3.4 Benefit-Cost Considerations 11
4. Other Factors to Consider 12
4.1 Planting Considerations 12
4.2 Maintenance 14
4.3 Safety 15
5. Urban Forestry Initiatives 15
6. Resources 19
6.1 Plant Selection 19
6.2 Benefit-Cost and Other Tools 21
6.3 General Information 24
Endnotes 26
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Trees and Vegetation
S hade trees and smaller plants such as shrubs, vines, grasses, and ground cover, help
cool the urban environment. Yet, many U.S. communities have lost trees and green
space as they have grown. This change is not inevitable. Many communities can take
advantage of existing space, such as grassy or barren areas, to increase their vegetative
cover and reap multiple benefits.
Opportunities to Expand the Use of Urban Trees
and Vegetation
Most U.S. communities have opportunities to increase the use of trees and vegeta-
tion. As part of the U.S. Environmental Protection Agency's (EPA's) Urban Heat Island
Pilot Project, the Lawrence Berkeley National Laboratory conducted analyses to
estimate baseline land use and tree cover information for the pilot program cities.1
Figure 1 shows the percentage of vegetated and barren land cover in four of these
urban areas. The high percentage of grass and barren land cover show the space po-
tentially available for
Figure 1: Land Cover Statistics for Various U.S. Cities
(Above Tree Canopy)
additional tree canopy
cover. The statistics do
not show the loss
of dense vegetated
cover as cities ex-
pand, however. For
example, a 2005
report estimates that
Houston lost 10 mil-
lion trees per year
from 1992 to 2000.2
30
25
< 15
% 10
5 -
Barren
Chicago
Houston
Sacramento Salt Lake City
TREES AND VEGETATION - DRAFT
1
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Figure 2: Vegetative Cover in New York City *|. How It Works
Trees and vegetation help cool urban climates
through shading and evapotranspiration.
Shading. Leaves and branches reduce
the amount of solar radiation that reaches
the area below the canopy of a tree or
plant. The amount of sunlight transmitted
through the canopy varies based on plant
species. In the summertime, generally 10 to
30 percent of the sun's energy reaches the
area below a tree, with the remainder be-
ing absorbed by leaves and used for pho-
tosynthesis, and some being reflected back
into the atmosphere. In winter, the range
of sunlight transmitted through a tree is
much wider—10 to 80 percent—because
evergreen and deciduous trees have dif-
ferent wintertime foliage, with deciduous
trees losing their leaves and allowing more
sunlight through.3
New York City reveals how developed areas (gray arid
white in this image) can replace vegetation (green).
Central Park is highlighted by the orange rectangle.
This chapter outlines some of the issues
communities might consider in determin-
ing whether and how to expand the use of
trees and vegetation so as to mitigate urban
heat island conditions. Among the topics
covered in this chapter are:
• How trees and vegetation reduce
temperatures
• Some of the benefits and costs associ-
ated with trees and vegetation
• Other factors a mitigation program
might consider
• Urban forestry initiatives
• Tools and resources for further
information.
Figure 3;Trees Shade a Home
Tree canopies, such as the deciduous trees around this
home in Virginia, can block much of the sunlight from
reaching the ground orthe building.
2
REDUCING URBAN HEAT ISLANDS - DRAFT
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Shading reduces surface temperatures
below the tree canopy. These cooler sur-
faces, in turn, reduce the heat transmitted
into buildings and the atmosphere. For
example, a multi-month study measured
maximum surface temperature reductions
ranging from 20 to 45°F (11-25°C) for walls
and roofs at two buildings.4 Another study
examined the effects of vines on wall tem-
peratures and found reductions of up to
36°F (20°C).5 A third study found that tree
shading reduces the temperatures inside
parked cars by about 45°F (25°C).6
Evapotranspiration. Trees and vegeta-
tion absorb water through their roots and
emit it through their leaves—this move-
ment of water is called "transpiration." A
large oak tree, for example, can transpire
40,000 gallons of water per year; an acre of
corn can transpire 3,000 to 4,000 gallons a
day.7 Evaporation, the conversion of water
from a liquid to a gas, also occurs from
the soil around vegetation and from trees
and vegetation as they intercept rainfall on
leaves and other surfaces. Together, these
Figure 4: Evapotranspiration
Plants take water from the ground through their roots
and emit it through their leaves, a process known as
transpiration. Water can also evaporate from tree surfaces,
such as the stalk, or surrounding soil.
processes are referred to as evapotranspi-
ration. Evapotranspiration cools the air by
using heat from the air to evaporate water.
Evapotranspiration, alone or in combina-
tion with shading, can help reduce peak
summer air temperatures. Various studies8-9
have measured the following reductions:
• Peak air temperatures in tree groves
that are 9°F (5°C) cooler than over
open terrain.
• Air temperatures over irrigated agri-
cultural fields that are 6°F (3°C) cooler
than air over bare ground.
• Suburban areas with mature trees that
are 4 to 6°F (2 to 3°C) cooler than new
suburbs without trees.
• Temperatures over grass sports fields
that are 2 to 4°F (1 to 2°C) cooler than
over bordering areas.
Trees and other large vegetation can also
serve as windbreaks or wind shields to
reduce the wind speed in the vicinity of
buildings. In the summertime, the impacts
can be positive and negative. In the win-
tertime, reducing wind speeds, particularly
cold north winds, can provide substantial
energy benefits.
2. Using Trees and Vegetation in
the Urban Landscape
Trees and vegetation are most useful as a
mitigation strategy when planted in strate-
gic locations around buildings. Researchers
have found that planting deciduous species
to the west is typically most effective for
cooling a building, especially if these trees
shade windows and part of the building's
roof. Shading the east side of a structure
also reduces air conditioning demand.10-11
Planting trees to the south generally lowers
summertime energy demand, but must be
Evapotranspiration
Transpiration
Stomata
Evaporation
TREES AND VEGETATION - DRAFT
3
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done carefully. Depending on the trees, the
building's height, and the distance between
the trees and a building, trees may be det-
rimental to an energy efficiency strategy if
they block useful solar energy in the win-
ter, when the sun is low in the sky, without
providing much shade during the summer,
when the sun is high in the sky
Shading pavement in parking lots and on
streets can be an effective way to help cool
a community. Trees can be planted around
perimeters and in medians inside parking
lots or along the length of streets. Strategi-
cally placed shade trees also can benefit
playgrounds, schoolyards, ball fields, and
similar open spaces.
Trees are not the only vegetation option.
There are many areas where trees either do
not fit or grow too slowly to be effective
over the short term, in which case vines
may work better. Vines need less soil and
Figure 6: Vines to Shade a Wall
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Vines grown on treliises can provide a quick,
simple source of shade.
space and grow very quickly. Vines grown
on the west side of a building, for example,
will shade the exterior wall and reduce its
surface temperature, thus reducing heat
gain inside the building. The vines will
provide some air cooling benefits through
evapotranspiration as well.
Figure 5: Tree Placement to Maximize Energy Savings
rrraa
rrma
-rrriH
frrw
tzrnw
rrmm
rw isi
Vines on treiiis
shade patio
Vines over
driveway
Shade
A/C Unit
Locate trees to west
or east of house
Locate trees at least
5-10'but less than
30-50'from house
Block winter winds with
evergreen trees
Picking the right trees and putting them in the right location will maximize their ability to shade
buildings and block winds throughout the year.
4
REDUCING URBAN HEAT ISLANDS - DRAFT
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3. Benefits and Costs
The use of trees and vegetation in the
urban environment brings many benefits,
including lower energy use, reduced air
pollution and greenhouse gas emissions,
protection from harmful exposure to ul-
traviolet (UY) rays, decreased stormwater
runoff, potential reduced pavement main-
tenance, and other quality-of-life benefits.
At the same time, communities must also
consider the costs of an urban forestry pro-
gram and any potential negative impacts of
increasing tree and vegetation cover. The
following sections address these benefits
and costs in more detail. Section 6 of this
chapter summarizes software tools that cal-
culate the range of potential benefits from
urban tree and vegetation initiatives.
U.S. Department of Agriculture
(USDA) Forest Service research cen-
ters offer links to publications about
studies of trees and their benefits to
urban areas. See and .
3.1 Benefits
Reduced Energy Use. Trees and vegeta-
tion that provide direct shading reduce
energy needed to cool buildings. Benefits
vary based on the orientation and size of
the plantings, as well as their distance from
a building. Large trees planted close to the
west side of a building will generally pro-
vide greater cooling energy savings than
other plants.
The examples below from a variety of stud-
ies highlight cooling and year-round en-
ergy savings from trees and vegetation.
• Joint studies by the Lawrence Berkeley
National Laboratory (LBNL) and the
Sacramento Municipal Utility District
(SMUD) placed varying numbers of trees
around houses to shade windows and
then measured the buildings' energy
use.12-13 The cooling energy savings
ranged between 7 and 47 percent and
were greatest when trees were planted to
the west and southwest of buildings.14
• A USDA Forest Service study inves-
tigated the energy savings resulting
from SMUD's residential tree planting
program. This study included over 250
program participants in the Sacra-
mento, California, area, and estimated
the effect of new shade trees planted
around houses. An average of 3 new
trees were planted within 10 feet (3 m)
of each house.15 Annual cooling energy
savings were 1 percent per tree, and
annual heating energy use decreased
by almost 2 percent per tree. The trees
provided net wintertime benefits be-
cause the positive wind shielding ef-
fect outweighed the negative effect of
added shade.
• Another LBNL study simulated the
effects of trees on homes in various
communities throughout the United
States. Assuming one tree was planted
to the west and another to the south
of a house, the model predicted that a
20-percent tree canopy over the house
would result in annual cooling savings
of 8 to 18 percent and annual heating
savings of 2 to 8 percent.16 Although
this particular model included ben-
efits from trees planted to the south of
a building, experts generally suggest
planting to the west and east of build-
ings, taking care when planting to the
south to avoid blocking desired solar
heat gain in the winter.17
TREES AND VEGETATION - DRAFT
5
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Reduced Air Pollution and Greenhouse
Gas Emissions. In addition to saving en-
ergy, the use of trees and vegetation as a
mitigation strategy can provide air quality
and greenhouse gas benefits:
• Leaves remove various pollutants from
the air, referred to as "dry deposition"
• Shade trees reduce evaporative emis-
sions from parked vehicles
• Trees and vegetation remove and
store carbon
• Trees and vegetation reduce green-
house gas emissions from power plants
by reducing energy demand.
Researchers have investigated the potential
for expanding urban tree and vegetative
cover to address air quality concerns, such
as ground-level ozone. One study pre-
dicted that increasing the urban canopy of
New York City by 10 percent could lower
ground-level ozone by about 3 percent,
which is significant, particularly in places
needing to decrease emissions to meet air
quality standards for this pollutant.18
Pollutant Removal through Dry Depo-
sition. Plants generally take up gaseous
pollutants, primarily through leaf stomata,
that then react with water inside the
plant to form acids and other chemicals.
Plants can also intercept particulate mat-
ter as wind currents blow particulates into
contact with the plants' surfaces. Some
particulates are absorbed into the plant
while others adhere to the surface, where
they can be resuspended into the atmo-
sphere by winds or washed off by rain to
the soil beneath.19 These processes can
reduce various pollutants found in the
urban environment, including particulate
matter (PM), nitrogen oxides (NOx), sulfur
dioxide (S02), carbon monoxide (CO), and
ground-level ozone (03).
Various studies have documented how
urban trees can reduce pollutants. A 2006
study estimated total annual air pollutant
removal by urban trees in the United States
at 784,000 tons, with a value of $3.8 bil-
lion.20 The study focused only on deposi-
tion of ground-level ozone, PM less than 10
microns in diameter (PM10), nitrogen diox-
ide (N02), S02, and CO. Although the esti-
mated changes in local ambient air quality
were modest, typically less than 1 percent,
the study noted that additional benefits
would be gained if urban temperature and
energy impacts from trees and vegetation
were also included.
Reduced Evaporative Emissions. Tree
shade can keep parked cars—particularly
their gas tanks—cooler, which lowers
evaporative emissions of volatile organic
compounds (YOCs), a critical precursor
pollutant in the formation of ground-level
ozone. Most large urban areas have a wide
range of control programs to reduce these
emissions, and tree shading programs can
be part of those strategies. For example,
one analysis predicted that light-duty
vehicle evaporative YOC emission rates
throughout Sacramento County could be
reduced by 2 percent per day if the com-
munity increased the tree canopy over
parking lots from 8 to 50 percent.21
Carbon Storage and Sequestration. As
trees grow, they remove carbon from the
atmosphere and store, or sequester, it. As
trees die or deposit litter and debris on the
ground, carbon is released to the atmo-
sphere or transferred to the soil. The net
effect of this carbon cycle is a substantial
level of carbon storage in trees, vegetation,
and soils.
The net rate of carbon sequestered by
urban trees in the continental United States
in 2005 is estimated to have been around
24 million tons per year (88.5 million tons
6
REDUCING URBAN HEAT ISLANDS - DRAFT
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Plants and Carbon:
Storage versus
Sequestration
Storage: Carbon currently held in
plant tissue (tree bole, branches, and
roots).
Sequestration: The estimated
amount of carbon removed annually
by plants, through the process of
photosynthesis.
C02eq)22, while current total carbon stor-
age in urban trees in the continental United
States is approximately 700 million tons of
carbon. The national average urban forest
carbon storage density is just over 25 tons
per hectare (100,000 square feet, or 9,300
m2), but varies widely from one community
to another and corresponds generally to
the percentage of land with tree cover and
to tree size and health.23 The California Air
Resources Board recently approved guide-
lines that will allow carbon sequestered
from forests to help meet the carbon emis-
sions reductions stipulated by California's
law AB32.24
Reduction in Greenhouse Gas Emis-
sions through Reduced Energy Demand.
As noted above, trees and vegetation can
decrease energy demand. To the extent that
reduced energy consumption decreases fos-
sil fuel burning in power plants, trees and
vegetation also contribute to lower carbon
emissions from those power plants. One
modeling study estimated that the direct
energy savings from shading alone by trees
and vegetation could reduce carbon emis-
sions in various U.S. metropolitan areas
by roughly 1.5 to 5 percent.25 The study
assumed that eight shade trees would be
placed strategically around residential and
office buildings and four around retail
stores. As urban forests also contribute to
air temperature reductions, the study found
that there would be additional reductions
in energy use and carbon emissions from
those indirect effects as well.
Full Life-cycle Carbon Reductions. In or-
der to investigate the full life-cycle impact
of urban trees on annual C02 emissions,
researchers consider:
• Annual C02 carbon sequestration rates
• Annual C02 releases from decomposition
• Annual C02 releases from maintenance
activities
• Annual C02 avoided emissions because
of reduced energy use.
By combining these four variables, re-
searchers can estimate the net C02 reduc-
tions from urban forest resources for a
specific community and calculate the asso-
ciated net monetary benefits. A 2006 field
study found that about 15,000 inventoried
street trees in Charleston, South Carolina,
were responsible for an annual net re-
duction of over 1,500 tons of C02. These
benefits were worth about $1.50 per tree,
based on average carbon credit prices.26
Improved Human Health. By reducing
air pollution, trees and vegetation lower
the negative health consequences of poor
air quality. Also, similar to the benefits of
cool roofs discussed in the "Cool Roof"
chapter, shade trees can reduce heat gain
in buildings, which can help lower indoor
air temperatures and minimize the health
impacts from summertime heat waves.
A third health benefit from trees and veg-
etation involves reducing direct exposure
to UV rays. The sun's UV rays can have
adverse health effects on the skin and eyes.
TREES AND VEGETATION - DRAFT
7
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High levels of long-term exposure to UY
rays are linked to skin cancer. The shade
provided by dense tree canopies can help
to lower UY exposure, although this should
not be considered a primary preventive
measure (see text box below).27-28
Enhanced Stormwater Management and
Water Quality. Urban forests, vegetation,
and soils can reduce stormwater runoff and
adverse impacts to water resources. Trees
and vegetation intercept rainfall, and the
exposed soils associated with plants absorb
water that will be returned to ground water
systems or used by plants.
Rainfall interception works best during
small rain events, which account for most
precipitation. With large rainfalls that con-
tinue beyond a certain threshold, vegeta-
tion begins to lose its ability to intercept
water. Stormwater retention further varies
by the extent and nature of a community's
urban forest. During the summer, with
trees in full leaf, evergreens and conifers in
Sacramento were found to intercept over
35 percent of the rainfall that hit them.29
Reduced Pavement Maintenance Costs.
Tree shade can reduce the deterioration of
street pavement. One field study compared
pavement condition data based on different
amounts of tree shade.30 The study found
that slurry resurfacing costs on a residen-
tial street could be reduced by approxi-
mately 15 to 60 percent, depending on the
type of shade trees used. Although the spe-
cific costs and benefits will vary based on
local conditions and paving practices, the
study suggests that pavement maintenance
benefits are another area to consider in
evaluating the potential benefits of a street
shade tree program.
Enhanced Quality of Life. Trees and veg-
etation can provide a range of quality-of-
life benefits. Adding trees and vegetation to
urban parks, streets, parking lots, or roofs
can provide a habitat for birds, insects, and
other living things. A well-placed row of
Reducing Exposure to UV Radiation
EPA's SunWise program promotes a variety of actions
people can take to reduce exposure to harmful UV radiation; seeking shade is just
one of them. To reduce the risk of skin cancer, cataracts, and other health effects, the
program recommends:
• Wearing a hat with a wide brim
• Wearing sunglasses that block 99 to 100 percent of UV radiation
• Always using sunscreen of SPF 15 or higher
• Covering up with long-sleeve, tightly woven clothing
• Watching for the UV Index to help plan outdoor activities when UV intensity
is lowest
• Avoiding sunlamps and tanning salons
• Limiting time in the midday sun (from 10:00 a.m. to 4:00 p.m.)
• Seeking shade whenever possible.
8
REDUCING URBAN HEAT ISLANDS - DRAFT
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Trees and Property Value Benefits
Many studies show that trees and other vegetative landscaping can increase property
values. For example, shopping centers with landscaping can be more prosperous
than those without, because shoppers may linger longer and purchase more.36-37-38-39
Other studies have found general increases of about 3 to 10 percent in residential
property values associated with the presence of trees and vegetation on a property.40
The specific impacts on residential property values vary widely based on the prop-
erty, the buyer's socioeconomic status, and other factors.
STRATUM, a USDA Forest Service tool that uses tree inventory data to evaluate the
benefits and costs of street and park trees, assumes an increase in residential prop-
erty values from tree planting measures. For an example, see the discussion on net
benefits and Figure 9 later in this chapter, which summarize data from a study that
used the STRATUM tool.41 In areas with high median residential sales prices, these
are often among the largest single category of benefits for a community.
trees and shrubs can reduce urban noise
by 3 to 5 decibels, while wide, dense belts
of mature trees can reduce noise by twice
that amount, which would be comparable
to noise reduction from effective highway
barriers.31 Urban trees and vegetation have
been linked to reduced crime,32 increased
property values,33 and other psychological
and social benefits that help decrease stress
and aggressive behavior.34-35
3.2 Potential Adverse Impacts
Before undertaking an urban forestry pro-
gram, it is important to know which types
of trees are likely to be most beneficial
and to avoid those that could cause other
problems. Evapotranspiration not only
cools the air but also adds moisture to it,
raising humidity levels. This increase may
be problematic in already humid climates.
However, there is little research on the hu-
man health and comfort trade-off between
temperature reductions and humidity in-
creases in different climates.
Although beneficial in limiting ground-level
ozone production by lowering air tempera-
ture and filtering ground-level ozone and
precursor pollutants from the air, trees and
other plants also emit YOCs. These emis-
sions are referred to as biogenic emissions.
The biogenic emissions from urban veg-
etation might counteract some of the air
quality benefits from trees. Biogenic YOC
emission rates, however, are in part depen-
dent on temperature. Thus, to the extent
that the increased use of trees and vegeta-
tion contributes to reduced temperatures,
the overall biogenic YOC emissions in an
urban area might still be reduced.42
Biogenic VOC emissions are affected by
sunlight, temperature, and humidity. The
emission rates of different tree species
vary tremendously; even trees in the same
For more information on the ozone-
forming potential (OFP) of various
trees, see
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family and genus show wide variation in
YOC emissions.Sfc'' Researchers calculate
an ozone-forming potential (OFP) value
to rate the potential effect a tree species
can have on ground-level ozone forma-
tion in a given environment. To minimize
the contribution to ground-level ozone, a
mitigation program can consider low-OFP
Figure 7: The Ozone-Forming Potential of Trees
species. Table 1 provides example OFP
ranges for common tree species in the Los
Angeles area. Communities can check with
USDA Forest Service staff in their region to
determine if there are additional resources
to help select low-OFP tree species for a
particular area and climate (see Table 5 for
links to regional Forest Service web sites).
Red maple, on the left, has a low ozone-forming potential,
whereas Oregon scrub oak, above, has a high potential.
Communities that want to plant trees may consider
biogenic emissions as well as other properties of trees,
such as their ability to survive in urban conditions.
Table 1: Examples of VOC Emissions from Trees in the Los Angeles Climate 45
Common Name
Genus and Species
Oaks
Ozone-Forming Potential
L | M | H
White Oak
Quercus alba
Oregon White Oak
Quercus garryana
Scrub Oak
Quercus laevis
S
Valley Oak
Quercus lobata
Pines
Sand Pine
Pinus clausa
/
Red Pine
Pinus densiflora
Longleaf Pine
Pinus palustris
Maples
Red Maple
Acer rubrum
Silver Maple
Acer floridanum
Citrus
Lisbon Lemon
Citrus limon
Meyer Lemon
Citrus limon 'Meyer'
Valencia Orange
Citrus sinensis 'Valencia'
10
REDUCING URBAN HEAT ISLANDS - DRAFT
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Other potential adverse effects include in-
creased water demand, additional solid wastes
from pruning and tree removal, and possible
damage to sidewalks, power lines, and other
infrastructure from roots or falling branches.
3.3 Costs
The primary costs associated with plant-
ing and maintaining trees or other vegeta-
tion include purchasing materials, initial
planting, and ongoing maintenance such
as pruning, pest and disease control, and
irrigation. Other costs include program
administration, lawsuits and liability, root
damage, and tree stump removal. However,
as the following section indicates, the ben-
efits of urban trees almost always outweigh
these costs.
3.4 Benefit-Cost Considerations
To help communities determine the value
of investments in urban trees and veg-
etation, groups have developed tools to
quantify the value of trees (see Section
6). These tools factor in the full range of
urban forest benefits and costs, such as
energy savings in buildings, air quality im-
provements, stormwater retention, property
value increases, and the value of mulch or
hardwood recovered during tree pruning
and removal. Some tools also track green-
house gas emissions or C02 reduction. The
tools weigh these benefits against the costs
of planting, pruning, watering, and other
maintenance throughout a tree's life.
In calculating benefits, it is important to
note that trees grow slowly, so it may take
as long as five years for some benefits from
trees, such as energy savings, to take effect.
After 15 years, an average tree usually has
matured enough to provide the full range
of benefits.46
Although the benefits can vary consider-
ably by community and tree species, they
Figure 8; Tree-Stump Removal
Tree programs will incur certain costs, such as tree
removal.
almost always outweigh the expense of
planting and maintaining trees. For ex-
ample, one five-city study found that, on a
per tree basis, cities accrued benefits rang-
ing from roughly $1.50 to $3-00 for every
dollar invested. These cities spent about
$15-65 annually per tree, with net benefits
ranging from approximately $30-90 per
tree. In all five cities, the benefits out-
weighed the costs, as shown in Figure 9-47
Figure 9 also compares how the categories
of annual costs and benefits associated
with trees varied between these cities.
Studies in California also have shown
net annual benefits ranging from zero to
about $85 per tree.4M9,50 community can
develop similar analyses for its mitigation
program. Places as diverse as Florence,
Alabama;51 Cedar Rapids, Iowa;52 Portland,
Oregon;53 and Hyattsville, Maryland,54 have
all quantified the net benefits of their trees.
See Section 6 for more resources on exist-
ing studies and tools that can aid this type
of assessment.
For a simple, online tree benefit cal-
culator, see .
TREES AND VEGETATION - DRAFT
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Figure 9: Total Annual Benefits versus Costs (Per Tree)
90.00
80.00
70.00
60.00
50.00
O 40.00
30.00
20.00
10.00
Ft Collins,
CO
Cheyenne,
WY
Bismarck,
ND
City
Berkeley,
CA
Glendale,
AZ
Benefits
¦ Property Value
¦ Stormwater
¦ Air Quality
~ C02
~ Energy
Costs
¦ Other Costs
~ Infrastructure & Liability
~ Pruning, Removal, & Disposal
~ Planting
Net benefits were positive for all five cities, ranging from $21 per tree in Cheyenne to $38 per tree in Ft. Collins. Blue and
green categories indicate benefits; red, orange, and yellow indicate costs.
4. Other Factors to Consider
4.1 Planting Considerations
Buildings
To reduce temperatures and cooling en-
ergy needs, trees planted for summer
shade should shelter western and eastern
windows and walls and have branches
high enough to maintain views or breezes
around the windows. Trees in these loca-
tions block the sun when it is at its low-
est angle: in the morning and afternoon.
Planting trees at least 5 to 10 feet (1.5 to
3 m) away from the building allows room
for growth, but shade trees should be no
more than 30 to 50 feet (9 to 15 m) away A
building with deciduous trees for summer
shade will also allow for winter heat gain
to the building, especially if branches are
pruned to maximize sun exposure.
It might also be beneficial to shade air con-
ditioner condenser units and other building
cooling equipment with trees, vines, or shrub-
bery, as these units work less efficiently when
hot. It is important to follow manufacturer
guidelines for ensuring adequate space to al-
low for proper air flow around the equipment.
In an urban setting, neighboring buildings,
driveways, fences, and other features can
make it difficult to follow these guidelines
for planting trees. The following are the
best use of trees and vegetation:
• Optimize the shade coverage from trees
planted in less favorable locations by
pruning tree branches to a height that
blocks the summer sun, yet lets the
winter sun through.
• Use bushes, shrubs, or vines to shade
windows and walls in places where
For overall energy efficiency, some
communities might promote the use of
evergreens to block winter winds and
reduce heating needs. A row of ever-
greens might be planted perpendicular
to the main wind direction, usually to
the north or northwest of a home.
12
REDUCING URBAN HEAT ISLANDS - DRAFT
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Figure 10: View of a Shaded Street
-------
Communities can consider the use
of hardy, native trees and plants in
selecting landscaping options. See
for further information.
vines on trellises over seating and other
areas, either in place of trees or as a first
phase of adding shade vegetation.
4.2 Maintenance
Education, skill, and commitment are
necessary for planting and maintaining an
aesthetically, environmentally, and structur-
ally effective urban landscape. By adhering
to good landscape design and maintenance
practices, many common problems may be
avoided. Local cooperative extension of-
fices can provide additional information on
soil conditions and other important consid-
erations. Also, local planting guides are of-
ten available from urban forestry agencies,
utility companies, arboricultural organiza-
tions, and plant nurseries. The following
are steps to consider when maintaining
trees in an urban area,58-59 helping vegeta-
tion grow faster and live a longer, healthier,
and more productive life.
• Choose the right plan ts. Because trees
and vegetation that are hardy enough to
survive in a specific climate require little
maintenance, communities might want
to start by considering native species.
Other characteristics to consider include:
- The vegetation's projected height
and canopy spread
- Size and growth habits of the roots
- The plant's sun, soil, water, and
temperature requirements
- The types of leaves, berries, and
flowers it produces
- Allergens and biogenic emissions
that can contribute to ground-level
ozone formation.
Local nonprofit tree organizations, coopera-
tive extension offices, urban foresters and
arborists, garden clubs, landscape archi-
tects, landscaping contractors, and other
groups can provide detailed information
about the best trees for a specific com-
munity's climate, along with advice about
planting and maintaining them. See Section
6 for a list of plant selection resources.
• Avoid maintenance problems. Com-
munities will want to avoid interfer-
ence with utilities, sidewalks, and other
infrastructure when planting trees to
avoid future maintenance problems.
Another important consideration is that
trees must have adequate soil and ac-
cess to water.
• Make arrangemen ts for regular care.
Especially in the early years after initial
planting, trees require regular mainte-
nance to survive. Maintenance require-
ments and costs generally decline after
a tree becomes established.
Figure 12: RegularTree Care
Proper pruning and other regular care will help
trees last longer and provide greater benefits to
the community.
14
REDUCING URBAN HEAT ISLANDS - DRAFT
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4.3 Safety
The use of trees and vegetation around
buildings can increase fire risks. Communi-
ties, especially those in fire prone areas,
can find information on tree selection and
placement that minimizes those risks:
• The National Interagency Fire Center
offers suggestions for tree placement
and landscape maintenance to avoid
losses to wildland fires. See .
• The USDA Forest Service helps home-
owners determine and minimize fire
risk from landscaping via an interactive,
graphical tool. See .
Project sponsors can also check with local
fire departments or street tree agencies to
evaluate and minimize fire risks for a spe-
cific tree and vegetation initiative.
5. Urban Forestry Initiatives
Communities can use various mechanisms
to increase their vegetative cover. These ef-
forts include forming public-private part-
nerships to encourage voluntary action in
the private sector to enacting ordinances.
As discussed in the chapter "Heat Island
Reduction Activities," communities already
have developed a wide range of voluntary
and policy approaches for using urban
trees and vegetation. For public-sector
projects, local governments and organiza-
tions have undertaken efforts to expand
the use of trees and vegetation in public
spaces and adopted minimum landscaping
policies for public buildings. Tree planting
programs, used throughout many commu-
nities, often involve collaboration with non-
profit groups and electric utilities. Some
states fund urban forestry program initia-
tives dedicated to addressing urban heat
islands and other community concerns.
Figure 13: Urban Forestry Surveys and Plantings
Urban forestry initiatives can take multiple forms, such
as creating an inventory of existing trees or planting
additional ones.
In addition, communities have enacted vari-
ous ordinances to foster the urban forest,
including those focused on:
• Tree protection
• Street trees
• Parking lot shade
• General landscaping.
The "Heat Island Reduction Activities" chap-
ter provides a detailed description of these
initiatives. Table 2 briefly summarizes them.
TREES AND VEGETATION - DRAFT
15
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Table 2: Examples of Urban Forestry Initiatives
Type of Initiative
Description
Links to Examples
Research
USDA Forest Service
programs
- USDA Forest Service operates research
centers throughout the United States, including the Pacific Southwest
Research Station, which specializes in urban forestry. USDA also collabo-
rates with states and universities; for example, the Northeast Center for
Urban and Community Forestry involves the Forest Service, the Univer-
sity of Massachusetts, and seven states.
University programs
- The
University ofWashington College of Forest Resources supports Human
Dimensions of Urban Forestry and Urban Greening, a research program
that focuses on the interaction of vegetation and humans in cities.
- A similar program at the University of Illinois,
Landscape and Human Health Laboratory, studies the connections be-
tween greenery and human health and behavior.
Voluntary efforts
Demonstration
projects
- Beginning in
2006, the Home Depot Foundation and the National Arbor Day Foun-
dation partnered together to plant 1,000 trees in 10 cities across the
country over a three-year period. This demonstration project is designed
to increase awareness of the importance of urban trees and to create
healthier communities in urban areas.
Incentive programs
- Trees for a Green
LA provides Los Angeles residents with free shade trees if they par-
ticipate in a tree planting and maintenance workshop and submit a
program application that includes a site plan.
- The Tree
Fund, a component of the Neighborhood Matching Fund, provides trees
to neighborhood groups in Seattle to enhance the city's urban forest.
The city government provides the trees, and neighbors share the work of
planting and caring for them.
Urban forestry
programs
-TreeVitalize is a public-private partnership that
uses regional collaboration to address the loss of tree cover in the five-
county Southeastern Pennsylvania region. Goals include planting 20,000
shade trees; restoring 1,000 acres of forests along streams and water pro-
tection areas; and training 2,000 citizens to plant and care for trees.
- Groundwork Elizabeth is a non-
profit corporation created to "foster sustainable community regenera-
tion" in Elizabeth, New Jersey. It is an outgrowth of a program developed
by the National Park Service called Groundwork USA.
Voluntary efforts
Urban forestry
- Million TreesLA is a cooperative effort
among the City of Los Angeles, community groups, businesses, and indi-
viduals working together to plant and provide long-term stewardship of
1 million trees.
16
REDUCING URBAN HEAT ISLANDS - DRAFT
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Table 2: Examples of Urban Forestry Initiatives (continued)
Type of Initiative
Description
Links to Examples
Outreach & educa-
tion
- EPA's Heat Island Reduction Initiative
provides information on the temperature, energy, and air quality impacts
from urban forestry and other heat island mitigation strategies.
- EPA's
Office of Water highlights design options, including trees and vegetation
that reduce stormwater runoff and water pollution.
-TreeUtah is a statewide, volunteer driven, non-
profit organization dedicated to tree planting and education. Since 1989,
TreeUtah has worked with over 100,000 volunteers to plant over 300,000
trees throughout Utah, providing training workshops for adults and
teens, education for elementary students, service learning opportunities
through the University of Utah, and alternative spring breakfor college
students to plant trees in urban neighborhoods.
- The Los Angeles
Cool Schools Program provides students with an educational curricu-
lum about trees and the environment, in addition to planting trees
around schools.
Policy efforts
Resolutions
-The Annapolis, Maryland, City Council estab-
lished an Energy Efficiency Task Force in 2005 to make recommendations
on how the city could reduce energy costs, energy consumption, and its
reliance upon foreign petroleum. One of the Task Force's recommenda-
tions was to increase the urban tree canopy to 50 percent of the city's
land area by 2036.The recommendations were approved by the City
Council in 2006.
- The Austin,Texas, City
Council adopted a resolution in 2001, acknowledging the urban heat
island and available mitigation efforts.The resolution called on the City
Manager to evaluate the fiscal impact and cost benefits of recommenda-
tions made by the City's Heat Island Working Group.
TREES AND VEGETATION - DRAFT
17
-------
Table 2: Examples of Urban Forestry Initiatives (continued)
Type of Initiative
Description
Links to Examples
Tree & landscape
ordinances
- Sacramento, California, has a performance-based
parking lot shading ordinance with detailed design and maintenance
guidelines to help owners with compliance.
- Austin's tree preserva-
tion ordinance specifies that new development projects are evaluated
on a case by case basis to ensure tree preservation and planting of high
quality native and adapted trees.
Policy efforts
State Implementa-
tion Plans (SIPs)
- This web site, sponsored by the USDA Forest
Service, evaluates options for including urban forest initiatives in a SIP, a
federally-enforceable air quality management plan.
-
This link provides materials available from a working session on issues
and ideas about incorporating urban forest initiatives into a SIP.
- This paper provides a brief summary of relevant EPA SIP guidance
and details actions to help facilitate the inclusion of urban tree canopy
increases within SIPs to meet clean air standards.
-This link profiles the Sac-
ramento, California, area project that is evaluating tree planting as a SIP
reduction strategy for ground-level ozone.
18
REDUCING URBAN HEAT ISLANDS - DRAFT
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6. Resources
Figure 14: Green Walls
6.1 Plant Selection
One of the key factors in a successful tree
or vegetation mitigation project is choosing
the right plants. Various web-based plant
selection guides are available, including
those listed in Table 3. For local informa-
tion on tree selection, communities can
contact tree planting organizations, com-
munity arborists, horticultural organiza-
tions, or landscape design consultants.
Also, the land development codes and
guidelines in many communities include
lists of recommended and prohibited
species, along with guidance on planting
methods and site selection.
f
In places where it may be difficult to plant more vegetation, green
roofs and green walls, such as this one on a store in Huntsville,
Alabama, offer an alternative. See the "Green Roofs" chapter.
TREES AND VEGETATION - DRAFT
19
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Table 3: Web-Based Plant Selection Guides*
Name
Description
General Information
Web Link
International Society of Arbori-
culture Tree Selection
Overview of variables to consider, including
tree function, form, size, and site conditions.
Databases
Tree Guide Advanced Search
Database of trees that can be searched by
variables including sun exposure, hardiness
zone, tree shape, and height.
PLANTS Database
Database of information about U.S. plants,
with an advance search by name, location,
and environmental variables, such as soil
type, fire tolerance, and flower color.
SelecTree for California
Database of California trees that can be
searched by name or environmental variable.
Lists of Recommended Trees
Tree Link
List of recommended trees by USDA hardi-
ness zone; links to regional tree information.
;
Recommended Urban Trees
Description of recommended urban trees for
USDA hardiness zones 1-6, listed by tree size
and planting conditions.
Cleaner Air.Tree by Tree: A
Best Management Practices
and Guide for Urban Trees in
Southern Nevada
Handbook for cultivating recommended
trees to mitigate urban heat islands in south-
ern Nevada.
Tree Selection Guide for
South Carolina
List of trees recommended for South
Carolina and tips on what to consider when
selecting trees.
* For information on the ozone-forming potential of various trees, see the list in Estimating the Ozone-forming Potential of Urban Trees and Shrubs/'11
20
REDUCING URBAN HEAT ISLANDS - DRAFT
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6.2 Benefit-Cost and Other Tools
Mitigation programs can use existing re-
search and tools to conduct benefit-cost
analyses for urban forest projects. Some of
these resources include:
Table 4: Urban Forestry Tools and Resources
Name | Description | Web Link
Tree Inventory, Benefit, and Cost Resources
/'-TREE software suite
Developed by the USDA Forest Service, the
/'-TREE software suite is available free-of-charge
on CD-ROM by request.The software suite uses
data gathered by the community to provide an
understanding of urban forest structure, infor-
mation on management concerns, cost-benefit
information, and storm damage assessment. The
software allows for analyses of a single street tree,
a neighborhood, or an entire urban forest. /'-Tree
combines STRATUM and UFOREthe Mobile Com-
munityTree Inventory (MCTI) (see below).
StreetTree Resource Analysis
Tool for Urban forest Managers
(STRATUM)
STRATUM is a USDA Forest Service tool that uses
tree inventory data to evaluate the benefits and
costs of street and park trees and estimate man-
agement needs.
Urban Forest Effects (UFORE)
UFORE is a USDA Forest Service tool that uses
tree inventory data to model and quantify urban
forest structure (e.g., species composition, tree
density, tree health, leaf area, leaf and tree bio-
mass, species diversity), environmental effects,
and value to communities.
The Mobile CommunityTree
Inventory (MCTI)
MCTI is a USDA Forest Service tree inventory tool
that can be customized to individual communities.
Data can be collected either by paper tally sheet,
ortheTree Inventory PDA Utility, which simplifies
data input. Data collected can then be used with
the STRATUM or UFORE applications.
ecoSmart
The Center for Urban Forest Research publishes a
web-based software program designed to evalu-
ate the economic trade-offs between different
landscape practices on residential parcels.The
program estimates the environmental and cost
impacts of strategic tree placement, rainfall man-
agement, and fire prevention practices.
TREES AND VEGETATION - DRAFT
21
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Table 4: Urban Forestry Tools and Resources (continued)
Name Description
Tree Inventory, Benefit, and Cost Resources (continuec
Web Link
)
Municipal Forest Resource
Analysis
The Center for Urban Forest Research publishes a
series of reports on benefits and costs of tree pro-
grams in various U.S. regions and communities.
See"Tree Guides"and
"Municipal Forest Resource
Analysis."
Urban Forestry Index (UFind)
Database of current and historic urban forestry
and arboriculture publications and other media
compiled by the USDA Forest Service, the Univer-
sity of Minnesota, and TreeLink with the goal of
increasing access to urban forestry material and
preventing duplication of products.
A Practical Approach to Assessing
Structure, Function, and Value of
StreetTree Populations in Small
Communities
This 14-page report gives step-by-step instruc-
tions for estimating benefits and costs of trees in
a specific community, using Davis, California as a
case study.
The Community and Urban For-
est Inventory and Management
Program (CUFIM)
Produced by the Urban Forest Ecosystems Insti-
tute of California Polytechnic State University,
the Community and Urban Forest Inventory and
Management Program (CUFIM) is a free Microsoft
Excel-based program that helps to inventory
urban trees and estimate an economic value of
wood recovery.
User guide:
Program files:
CITYgreen
American Forests developed CITYgreen, a graphi-
cal information system application based on
the UFORE model that is available for purchase.
The software calculates ecologic and economic
benefits from urban trees, including energy sav-
ings, air quality, stormwater improvements, water
quality, and carbon storage and sequestration.
CITYgreen also models changes in land cover and
can be used in planning green infrastructure.
Comfort Tool
OUTdoor COMfort Expert System
(OUTCOMES)
The USDA Forest Service developed the OUTdoor
COMfort Expert System (OUTCOMES), which
calculates a human comfort index by considering
weather variables, tree density and shade pattern,
and other neighborhood features.
22
REDUCING URBAN HEAT ISLANDS - DRAFT
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Table 4: Urban Forestry Tools and Resources (continued)
Name
Description
Carbon Calculators
Web Link
Individual tree carbon calculators
The USDA Forest Service has developed spread-
sheet programs to estimate the carbon storage
and sequestration rates for a sugar maple and
a white pine.These spreadsheets provide a
rough approximation of tree carbon storage and
sequestration rates based on user-inputs of tree
growth rates.
Carbon dioxide calculators for
urban forestry
The USDA Forest Service provides guidelines for
urban foresters and arborists, municipalities, utili-
ties, and others to determine the effects of urban
forests on atmospheric C02 reduction.
Method for
Calculating Carbon Sequestration
byTrees in
Urban and Suburban Settings
The Department of Energy has developed guid-
ance to calculate carbon sequestration by trees
in urban and suburban settings.The guidance is
intended for participants in the Voluntary Report-
ing of Greenhouse Gases Program and provides a
methodology and worksheet for calculations.
TREES AND VEGETATION - DRAFT
23
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6.3 General Information
Table 5 lists organizations and web sites
that contain additional information and
reference materials on urban forestry.
Table 5: Urban Forestry Organizations and Web Sites
Name Description Web Link
Center for Urban Forest Research,
part of the USDA Forest Service's
Pacific Southwest Research Sta-
tion
Publishes research on the benefits and
costs of urban trees, including urban heat
island, energy, air quality, climate change,
and water impacts. Is involved with
developing the California urban forestry
greenhouse gas reporting protocol and
developed STRATUM and ecoSMART.
Urban Forest Research Unit, part
of the USDA Forest Service's
Northeastern Research Station
Provides research on urban forest struc-
ture and the quantification of urban
forest benefits, particularly air quality.
Developed the UFORE and COMFORT
models and conducts national urban
forest assessments.
< www.fs.fed. us/n e/sy ra cu se>
Urban Natural Research Institute,
part of the USDA Forest Service
Northern Research Station
Provides monthly web casts and other
online resources targeted to the science
of urban forestry.
Urban and Community Forestry
Program, Northeastern Area, part
of the USDA Forest Service's State
and Private Forestry mission area
Resources on tree planting and care, ur-
ban forest management, and outreach
and marketing. The Urban and Commu-
nity Forestry Program provides techni-
cal, financial, educational, and research
services to states, cities, and nonprofit
groups so they can plant, protect, main-
tain, and utilize wood from community
trees and forests to maximize environ-
mental, social, and economic benefits.
Urban Forestry South,
part of the USDA Forest Service's
Southern Research Station
Published the Urban Forestry manual,
a 12-chapter guidebook including
cost-benefit information, public policy
strategies, and tree planting sugges-
tions. Urban Forestry South also hosts
the Tree Failure Database.
TreeLink
Provides a links database, listserves, web
casts, advice on grant writing, and links
to local community forestry groups.
< www.t ree 1 i n k.o rg >
24
REDUCING URBAN HEAT ISLANDS - DRAFT
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Table 5: Urban Forestry Organizations and Web Sites (continued)
Name
Description
Web Link
National Alliance for Community
Trees (ACT)
Operates the NeighborWoods Program,
offering grants to community forestry
groups.The web site also has links to
local community forestry groups, public
policy updates, case studies of tree
planting programs, a media kit, and a
bi-monthly e-newsletter, and monthly
web casts.
National Arbor Day Foundation
Provides information about local tree
planting programs and events and
resources for environmental educators
and parents.
Sustainable Urban Landscape
Information Series
Covers urban landscape design, plant
selection, installation, and maintenance.
American Society of Landscape
Architects (ASLA)
Professional association for landscape
architects. Includes a search tool to
locate ASLA firms. ASLA is developing a
sustainability rating system for land-
scaped sites, comparable to the USGBC
LEED standard for buildings, as well as
regional guides to best practices.
TREES AND VEGETATION - DRAFT
25
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Endnotes
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Study of Metropolitan Chicago, Illinois. Paper LBNL-49275. Lawrence Berkeley National Labora-
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2 Nowak, D.J., Principal Investigator. 2005. Houston's Regional Forest. U.S. Forest Service and
Texas Forest Service. September 2005.
3 Huang, J., H. Akbari, and H. Taha. 1990. The Wind-Shielding and Shading Effects of Trees on
Residential Heating and Cooling Requirements. ASHRAE Winter Meeting, American Society of
Heating, Refrigerating and Air-Conditioning Engineers. Atlanta, Georgia.
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8 Huang, J., H. Akbari, and H. Taha. 1990. The Wind-Shielding and Shading Effects of Trees on
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32 Kuo, Francis E. and W.C. Sullivan. 2001. Environment and Crime in the Inner City: Does Vegeta-
tion Reduce Crime? Environment and Behavior. 33(3):343-367.
33 Laverne, R.J. and K. Winson-Geideman. 2003. The Influence of Trees and Landscaping on Rental
Rates at Office Buildings. Journal of Arboriculture. 29(5):281-290.
34 Wolf, K. 1998. Urban Nature Benefits: Psycho-Social Dimensions of People and Plants. Center
for Urban Horticulture, College of Forest Resources, University of Washington, Fact Sheet #1.
Seattle, WA.
35 Hansmann, R., S.M. Hug, and K. Seeland. Restoration and stress relief through physical activities
in forests and parks. Urban Forestry & Urban Greening. 6(4):213-225.
36 Wolf, K. 1998. Growing with Green: Business Districts and the Urban Forest. Center for Urban
Horticulture, College of Forest Resources, University of Washington, Fact Sheet #2. Seattle, WA.
37 Wolf, K. 1998. Trees in Business Districts: Comparing Values of Consumers and Business. Center
for Urban Horticulture, College of Forest Resources, University of Washington, Fact Sheet #4.
Seattle, WA.
38 Wolf, K. 1998. Trees in Business Districts: Positive Effects on Consumer Behavior. Center for Urban
Horticulture, College of Forest Resources, University of Washington, Fact Sheet #5. Seattle, WA.
39 Wolf, K. 1998d. Urban Forest Values: Economic Benefits of Trees in Cities. Center for Urban
Horticulture, College of Forest Resources, University of Washington, Fact Sheet #3. Seattle, WA.
40 The values cited for the increase in selling price reflect both the literature reviews and the
new data in: Des Rosiers, F., M. Theriault, Y. Kestans, and P. Villeneuve. 2002. Landscaping
and House Values: An Empirical Investigation. Journal of Real Estate Research. 23(1):139-162.
Theriault, M., Y. Kestens, and F. Des Rosiers. 2002. The Impact of Mature Trees on House Values
and on Residential Location Choices in Quebec City. In: Rizzoli, A.E. and Jakeman, A.J. (eds.).
Integrated Assessment and Decision Support, Proceedings of the First Biennial Meeting of the
International Environmental Modeling and Software Society. iEMSs, 2002.1:478-483.
41 McPherson, E.G., J.R. Simpson, P.J. Peper, S.E. Maco, and Q. Xiao. 2005. Municipal Forest Ben-
efits and Costs in Five US Cities. Journal of Forestry. 103(8):4l 1-416.
42 Nowak, D.J. 2000. The Effects of Urban Trees on Air Quality. USDA Forest Service: 4. Syracuse, NY.
43 Benjamin, M.T., M. Sudol, L. Bloch, and A.M. Winer. 1996. Low-Emitting Urban Forests: a Taxo-
nomic Methodology for Assigning Isoprene and Monoterpene Emission Rates. Atmospheric
Environment. 30(9): 1437-1452.
44 Benjamin, M.T. and A.M. Winer. 1998. Estimating the Ozone-Forming Potential of Urban Trees
and Shrubs. Atmospheric Environment. 32(l):53-68.
45 Benjamin, M.T. and A.M. Winer. 1998. Estimating the Ozone-Forming Potential of Urban Trees
and Shrubs. Atmospheric Environment. 32(l):53-68.
46 McPherson, E.G. 2002. Green Plants or Power Plants? Center for Urban Forest Research. Davis, CA.
47 McPherson, E.G., J.R. Simpson, P.J. Peper, S.E. Maco, and Q. Xiao. 2005. Municipal Forest Ben-
efits and Costs in Five US Cities. Journal of Forestry. 103(8):4l 1-416.
28
REDUCING URBAN HEAT ISLANDS - DRAFT
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48 McPherson, E.G., J.R. Simpson, P.J. Peper, K.I. Scott, and Q. Xiao. 2000. Tree Guidelines for
Coastal Southern California Communities. Local Government Commission & Western Center for
Urban Forest Research and Education. Sacramento, CA.
49 McPherson, E.G., J.R. Simpson, P.J. Peper, and Q. Xiao. 1999. Benefit-Cost Analysis of Modesto's
Municipal Urban Forest. Journal of Arboriculture. 25(5):235-248.
50 McPherson, E.G., J.R. Simpson, P.J. Peper, Q. Xiao, D.R. Pettinger, and D.R. Hodel. 2001. Tree
Guidelines for Inland Empire Communities. Local Government Commission & Western Center
for Urban Forest Research and Education. Sacramento, CA.
51 Stokes, Trevor. 2007. Trees give more to the community than shade. Times Daily. 24 No-
vember. Retrieved 14 January 2008 from .
52 Hadish, C. 2007. Benefits of trees measured. Gazette. 15 October. Retrieved 16 Octo-
ber 2007 from .
53 Portland Parks and Recreation. 2007. Portland's Urban Forest Canopy: Assessment and Public
Tree Evaluation. Retrieved 2 October 2007 from .
54 Maryland Department of Natural Resources Forest Service. 2007. New DNR Study Shows
Hyattsville's Trees Benefit The Bay, Save On Energy Bills And Mitigate Global Warm-
ing. 29 October. Retrieved 1 November 2007 from .
55 McPherson, E.G. 2001. Sacramento's parking lot shading ordinance: environmental and econom-
ic costs of compliance. Landscape and Urban Planning. 57:105-123.
56 City of Davis. 1998. Parking Lot Shading Guidelines and Master Parking Lot Tree List Guide-
lines. Davis, CA.
57 City of Sacramento. 2003. Tree Shading Requirements for Surface Parking Lots. Sacramento, CA.
58 McPherson, E.G. and J.R. Simpson. 2000. Carbon Dioxide Reduction through Urban Forestry:
Guidelines for Professional and Volunteer Tree Planters. PSW GTQ-171. USDA Forest Service,
Pacific Southwest Research Station.
59 Tree City, U.S.A. 2001. Tree Care Information. National Arbor Day Foundation, Tree City USA
bulletin 19. Nebraska City, NE.
60 Benjamin, M.T., and A.M. Winer. 1998. Estimating the Ozone-Forming Potential of Urban Trees
and Shrubs. Atmospheric Environment. 32(l):53-68.
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