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INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
Municipal Street Tree Structure and Ecosystem Services
Introduction
Green infrastructure refers to systems
that use vegetation, soils, and natural
processes to create healthier urban
environments. Green infrastructure-
based stormwater management systems
mimic natural hydrology to take
advantage of interception,
evapotranspiration, and infiltration of
stormwater runoff, reducing the strain
on traditional gray infrastructure
solutions like stormwater pipes and
sewers.
Municipal street trees are trees in the
public right-of-way and are a key part
of public green infrastructure in many
cities. Street trees provide benefits that
promote sustainability and help
alleviate environmental problems.
Collectively known as ecosystem
services, these benefits range from
improved air quality to reduced
stormwater runoff to aesthetic values.
Like other types of green
infrastructure, street trees require
substantial investments from local
governments, but they can provide a
return on the investment. In a study of
street trees in five U.S. cities, annual
ecosystem service benefits were valued
at $1.37 to $3.09 for each dollar spent
on management.l Given the importance
of municipal street trees in urban
environments, it is critical to
understand the drivers and
consequences of uneven street tree
distribution. This knowledge will help
protect economic investments and
guide effective street tree management.
Current Research
During the fall of 2013, EPA initiated
street tree research in the greater
Cincinnati, Ohio, metropolitan area.
Scientists are aiming to understand
how street tree structure and associated
benefits vary according to municipal
management practices, socioeconomic
conditions, and geographic setting.
EPA is addressing the following
questions through street tree research:
(1) Can street tree structure (i.e.,
numbers, sizes, and species
composition) and associated benefits
be explained by management practices,
socioeconomic conditions, or historical
or geographic factors? If so, which
factors are most important?
(2) How might invasive pests affect
street trees and associated benefits?
Which communities are most at risk
for pest devastation? What
management strategies could best
maintain street trees through a pest
outbreak and into the future?
(3) How will existing street tree
structure and associated benefits
change in the future under various
scenarios of tree growth and mortality,
management practices, and unexpected
events like pest outbreaks?
Most comparable street tree studies
have been conducted within a single
city. However, considering broader
patterns in a surrounding metropolitan
area is important because suburbs are
geographically larger, contain more
residents, and are often changing faster
than their respective urban centers.2 In
this study, researchers randomly
selected nine communities in the
greater Cincinnati area to span a range
of geographic settings, socioeconomic
characteristics, and street tree
management practices.
Scientific literature indicates that urban
forest cover, and street trees in
particular, often vary across cities in
Street trees increase a neighborhood's
visual appeal and provide important
ecosystem services. (Photo by A. Berland)
relation to factors such as race, wealth,
participation in tree programs, and
neighborhood age.3 This study includes
investigating how neighborhood
socioeconomic characteristics, such as
high-poverty, may be related to
investments in municipal street trees.
Any environmental justice issues, i.e.,
disproportionate investments and
associated benefits, will be reported.
In each community, researchers
randomly sampled about 10% of the
total length of local public streets and
made observations for individual street
segments, which are typically one
block long. At each street segment,
researchers recorded for each tree its
species, diameter at breast height, total
height, leaf crown width, and general
health, and noted interference with
power lines and sidewalks.
Status
To date, researchers have sampled over
53 miles of street right-of-way along
more than 600 street segments and
inventoried nearly 3,000 trees. The
most common trees are Gallery pear
(25%), crabapple (10%), silver maple
(7%), white ash (7%), red maple (6%),
and honeylocust (5%).
U.S. Environmental Protection Agency
Office of Research and Development
EPA 600/F-13/355
March 2014
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Street tree benefits will be estimated
using the USDA's Forest Service
model, i-Tree Streets.4 This model uses
sampling data to estimate, in both
native units and dollar values. The
benefits associated with street trees are
stormwater interception, carbon
storage and sequestration, air quality
improvement, energy savings, and
property value increases.
Analysis is underway to examine street
tree benefits and community
characteristics such as management
practices, socioeconomics, and
geographic setting. Preliminary results
indicate that management practices are
very important, with Tree City USA
participants yielding higher street tree
benefits than non-participants.
Researchers plan to assess the benefits
in the context of management costs to
determine if, and to what extent, these
benefits outweigh costs.
Results to date show no sign that street
trees and associated benefits are
distributed inequitably according to
race or wealth across the nine study
communities. However, preliminary
results contradict previous research
showing that neighborhood age relates
to community-scale benefits.
Researchers will conduct more detailed
analyses in the coming months.
Products
Expected deliverables from this project
include:
• street tree inventory data that can be
shared with interested community
officials
• a list of community characteristics
that influence street tree structure and
associated ecosystem services to aid
in urban forest management
• presentations at scientific and
professional conferences
• peer-reviewed journal articles
Partner Communities
EPA is working in nine communities in
the greater Cincinnati area. These
include the Cincinnati neighborhoods
of Hyde Park, Madisonville, and
Oakley, as well as the cities of
Fairfield, Forest Park, Mt. Healthy,
Reading, Springdale, and Wyoming.
Above, a residential street in the Cincinnati,
Ohio, metropolitan area includes street
trees. (Photo by A. Berland)
Contacts
Matt Hopton, Ph.D.
513-569-7718,
hopton.matthew@epa.gov
Adam Berland, Ph.D.
513-569-7247,
berland.adam@epa.gov
References
1 McPherson EG, et al. (2005). Municipal
Forest Benefits and Costs in Five US
Cities. Journal of Forestry 103: 411-416.
2 Berland A. 2012. Long-term urbanization
effects on tree canopy cover along an
urban-rural gradient. Urban Ecosystems 15:
721-738.
3 Landry SM and Chakraborty J. 2009.
Street Tree and Equity: Evaluating the
Spatial Distribution of an Urban Amenity.
Environment and Planning A 41: 2651-
2670.
4 USDA Forest Service. i-Tree Streets.
URL: http://itreetools.org/streets
5 Arbor Day Foundation. Tree City USA.
URL:
http://www.arborday.org/programs/treeCitv
USA
U.S. Environmental Protection Agency
Office of Research and Development
EPA 600/F-13/355
March 2014
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