Benefits of Urban Forests: Shady Cities for Sustainable Development

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Shady Cities as Part of Sustainable Development:
Benefits of the Urban Forest
By Kelly Murphy

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Kelly Murphy
November 13, 2014
Shady Cities as part of Sustainable Development:
Benefits of the Urban Forest
Implementing a thriving urban forest into major metropolitan areas is an essential
element of sustainable urban development. Maintenance and implementation of street
trees and vegetation into the urban landscape requires some investment; however, there
are important social, aesthetic, environmental and economic benefits of the urban canopy.
My research will aim at answering some of the following guiding questions – What are
the benefits of implementing and maintaining the urban forest? How much investment is
required for the development of a healthy urban forest, and what are the tradeoffs?
Introduction: Why is this topic relevant and what is the focus of this research?
The relevance of this issue exists on a global scale; with increasing population
magnitude throughout the world, we see an increase in the population density of urban
areas. According to the U.S. Census of 2000, approximately 80% of the U.S. population
now lives in urban areas. Major metropolitan areas tend to contribute more industrial
pollution and greenhouse gases. It is also important to consider the potential social
impacts that increased density has on the community. Urban forests have the ability to
reduce greenhouse gasses (primarily carbon dioxide) in the atmosphere, reduce spending
on heating/cooling, provide habitat for wildlife and encourage the biodiversity of an area,
intercept stormwater and reduce spending on water treatment and processing, and
contribute positively to the aesthetics of the urban landscape. My research focuses on

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identifying the benefits of the urban canopy and analyzes case studies of cities that have
achieved thriving eco-urban environments through successful urban forest management.
I hypothesize that my research will reflect the significance of the urban forest in
sustainable development, and will affirm the need to prioritize the implementation and
management of street trees and sustainable vegetation into the built urban environment. I
will provide statistical research on financial savings from shaded cities, tree population
counts, greenhouse gas emissions, flood prevention potential, as well as suggest strategies
for management and development. I will include case studies of 4 cities with the most
highly acclaimed urban forests, consisting of Sydney, Sacramento, Portland, and New
York. Finally, I will compare their management plans with the City of Chico’s General
Plan and Urban Forest Management Plan to analyze the quality of our urban canopy.
Section 1: Environmental benefits
Urban forests can be defined as ecosystems made up of trees and vegetation
within the built environment. Specifically, I studied street trees and other vegetation
planted on public land, for public use and enjoyment. There are many environmental
benefits to the implementation of city trees and development of urban forestry
management plans. Several statistical, scientific and technological studies have been
conducted to determine the ecological affects of urban forests. Air quality has the
potential to be improved through implementation of city trees and vegetation; urban trees
help mitigate greenhouse gas emissions (CO2) from industrial pollution and traffic smog.
This is possible through photosynthesis, since plant life needs carbon dioxide to absorb.
Urban trees emit biogenic volatile hydrocarbons (BVOCs), which can increase ozone
levels in cities (Manning 2008, 362-70). Global warming is attributed to increased levels

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of greenhouse gases in the atmosphere. Greenhouse gases contribute negatively to the
ozone layer, reducing it and making it thinner. This reduction to the ozone layer allows
more harmful ultraviolet (UV) rays to penetrate the Earth’s atmosphere. All forms of life
can be negatively affected by too much exposure to UV light, which can cause damage to
plants and trees and increase respiratory problems for people living in areas with high
concentrations of greenhouse gas emissions (i.e. vehicle exhaust, smog, industrial
pollution). The BVOCs given off by street trees and vegetation of the urban forest help
increase ozone levels by sequestering greenhouse gases (primarily CO2) and reducing
exposure to UV light and climate change affects.
The heat island effect describes how the heat absorbed by buildings, roads and
pavement then heats the surrounding air. Without trees for shade and transpiration
cooling, dense urban areas are dependent on heating and air conditioning. Transpiration
cooling involves the amount of energy required to absorb and evaporate water. For
example, a tree absorbs energy in liquid water through its roots, which is released as
vapor through its leaves; this results in a cooling of the nearby area and the plant tissue.
In order to maintain an energy balance, 25 percent of radiation received from the Sun is
absorbed through evapotranspiration. Without vegetation rains will not recharge into the
groundwater and the heat island effect will be intensified; stormwater systems have an
increased potential of being overwhelmed, contributing to urban run-off and pollution
and possibly leading to contamination of a water supply in an area (Manning 2008, 362-
70).
Through efficient forestry management, important wildlife habitat and water
resources can be protected, while fossil fuel consumption and greenhouse gas emissions

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can be reduced (Gatrell and Jensen 2002, 331-50). CITYgreen is a GIS based software
program capable of mapping, calculating and analyzing data such as energy savings, air
quality, emissions, and wildlife habitat within urban ecosystems (Dwyer 1999). Utilizing
these kinds of technology help identify target areas, gather and analyze data and project it
spatially onto a map for visual communication. Urban forests provide essential resources
for bird species, insects and small animals native to the region. The urban forest serves as
the ecological skeleton for all basic ecosystem functions in highly modified urban areas
(Wang 2013). Ultimately, the environmental benefits of the urban forest are intertwined
with the social and aesthetic advantages.
Section 2: Social and aesthetic advantages
In a 2004 survey funded by the U.S. Forest Service Urban and Community
Forestry Program, residents of major metropolitan cities nationwide were questioned
about their thoughts on the urban forest, as well as some background demographic
information. The survey consisted of a statement to which the participant could select a
rating on a scale from 1 to 4 (1=disagree, 2= neutral, 3= agree, 4=strongly agree).
Overall, the public rated the social, ecological and economic advantages of trees in their
cities highly (Lohr 2004, 28-35). The highest ranked reason for supporting urban forestry
was the shading and cooling benefits of trees in downtown areas, followed by the
psychological benefits that trees stimulate feelings of calmness and relaxation. These
results suggest that trees are appreciated for their aesthetic appeal as well as for their
contributions to social well-being. Other high-rated reasons identified reductions to smog
and noise as significant benefits of urban forests (see Tables 1). Some practical problems
of city trees were cited, including allergies, obstructing the view of store signs, and root

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damage to sidewalks (see Table 2); however, none of the 2,000 participants
acknowledged budgetary concerns as a significant factor (Lohr 2004, 28-35).
Source: Lohr 2004, 28-35
The positive results yielded from the
survey study are encouraging, since community involvement is critical to ensure the
vitality of urban forests (USDA 1996; Dwyer 2002). Urban forest development creates
recreational and leisure areas through public parks and green spaces, increases
biodiversity from available natural habitat, decreases feelings of stress and makes cities
more livable (Gatrell and Jensen 2002, 331-50). The ability of the urban canopy to
reduce the heat island effect is beneficial for everyone; trees and vegetation alter the
albedo (amount of light reflected by a surface) of urban environments, helping to cool
their surrounding area through transpiration and the provision of shade (Gatrell and
Jensen 2002, 331-50). Shady cities with successful urban forests are more appealing, and

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increase the social and economic value of an area. Economic benefits of urban forest
development are closely related with positive social impacts, such as increases to
property values.
Section 3: Economic tradeoffs
Properties are able to benefit from the amenities provided by the urban forest,
such as reduced energy bills and a decrease in the heat island effect. Properties shaded by
the urban tree canopy become attractive to buyers for the aesthetic qualities trees provide,
as well as their affect on air quality and energy savings. According to a Finnish study,
homes with access to urban forest amenities increase in value by nearly 5% (Gatrell and
Jensen 2002, 331-50). These economic benefits aren’t specific to select urban areas; the
reduced utility costs and increase in property values is advantageous to all urbanites.
Urban forestry programs should budget $2 per capita, annually, for maintenance
and management, according to the Arbor Day Foundation (see appendix A). Expenses
include city worker salaries, tree purchases, watering and fertilizing, pest control, dead
tree removal, pruning, leaf pickup, biomass recycling and equipment purchases (for a
complete list of expenditures, visit www.arborday.org). Other costs to consider are fire
potential and flammability risk, potential damage from by trees to infrastructure during
storms, and reduced visibility (Wang 2013). This investment yields direct and indirect
rewards; long-term benefits of urban forests include reduced costs in road maintenance,
flood control, water treatment and consumption, even healthcare (Gatrell and Jensen
2002, 331-50). The negative externalities of air pollution, resource consumption, and
non-green land uses should also be taken into account (Gatrell and Jensen 2002, 331-50).
To clarify, it would be more costly for cities to pay for utilities, water resources, water

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treatment, air quality improvements, habitat installation and wildlife programs, and/or
legislation to reduce greenhouse gas emissions than to invest upfront in a healthy urban
forest management plan.
Section 4: Case studies – Cities with the most successful urban forests
Sacramento Municipal Utility District’s shade tree program is an example of the
first comprehensive plan that showed significant economic savings in energy
consumption and utility costs (McPherson, Scott, & Simpson, 1998). Sacramento’s tree
canopy covers 17% of the city (see Figure 1); as of 2010 the city’s urban forest contained
over 115,000 trees. The non-profit Sacramento Tree Foundation planted an additional
23,000 new trees at the end of 2010, which are estimated to provide more than $6.5
million dollars annually in net energy savings, nearly $20 million in air quality benefits,
and over $10 million dollars in property value increases (American Forests 2014).
Figure 1. Sacramento’s Urban Forest
P
P
E
Source: www.arborday.com

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Perhaps this is a reason why the American Forests organization named
Sacramento one of its top ten cities with successful urban forests. The project was
sponsored by the U.S. Forest Service’s Urban and Community Forest Program. Using
city statistics such as population, park area by acres, tree species identification and tree
counts, the study evaluated the urban forest implementation and management plans of
cities nationwide to determine which urban areas had benefited the most from its urban
forest (American Forests 2014). Alongside Sacramento, Portland, Charlotte, Austin,
Denver, Milwaukee, Minneapolis, New York, Washington D.C. and Seattle were named
within the top ten.
New York is an East Coast example of a major metropolis with a thriving urban
forest. Tree canopy covers 21% of the city’s area of 300 square miles. This impressive
canopy can be largely attributed to its extensive park space (i.e. Central Park). New York
City’s population has increased to a staggering eight million; even with significant
population density and limited land resources, the comprehensive plans for the city have
always prioritized and maintained a healthy urban forest (see Figure 2).
Figure 2. New York’s Urban Forest, Central Park

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With a goal set by NYC’s mayor to plant a million trees by 2017, community
participation and partnership is necessary. The city’s thriving urban forest is able to
remove more than 2,000 tons of pollution from the atmosphere annually (a value of over
$10 million).
Successful urban forestry management plans prioritize the aesthetic, social and
environmental benefits of integrating nature into the built environment. Urban areas
require the aid of natural ecological processes to maintain a balance within the urban
landscape. Sydney, Australia is another urban center that is acknowledged for its close
connection to nature and thriving eco-urban environment (see Figure 3).
Figure 3. Urban Forest design in Sydney, Australia
The City of Sydney Urban Forest Strategy was adopted in February of 2013, and
highlighted plans to enhance and maintain a healthy urban forest. The cleaner air effects

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and reduction to inland temperatures are cited as main objectives in the Sydney Urban
Forest Strategy, as well as the crucial need to provide habitat for Australia’s diverse
wildlife. Sydney, the largest metropolitan area in Australia, faces many of the same
problems as large cities worldwide; its unique topographic characteristics create barriers
for north-south movement of biodiversity (Wang 2013). These boundaries include the
Tasman Sea to the east, and forested highlands to the west, with a geography deeply
intersected by streams, rocky ridges and varying elevation. For these reasons, the
community and local planning agencies of the city took action and created the Urban
Forest Strategy. This plan, backed by community support and appropriate budget
allocations, has been immensely successful for the metropolitan area. Specific elements
of this plan discussed which trees were most feasible and efficient, as well as the scale of
street trees to the surrounding area. For example, careful consideration of the local
climate, geology and topography is important, as well as the species of trees to
implement. Deciduous trees are often a good choice, since they provide the shade
benefits during summer, and allow exposure to solar energy and surface heat during the
winter. In addition, the larger the tree, the larger its canopy and ability to absorb air
pollutants; however, larger trees have the potential to cause more damage and might not
be the best choice on narrow streets with power lines, pedestrians, parked cars and
residential homes.
Portland is renowned for being a leader in sustainable urban development, and has
an impressive urban canopy that shades 30 percent of the city (see Figure 4).
Figure 4. Portland, CA Urban Forest

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The city is home to over 1.4 million trees, which cost approximately $6.5 million
annually to maintain. However, the environmental benefits total nearly $40 million taking
into account the tonnage of carbon sequestration and reduction in energy cost and
consumption. For every dollar invested in the urban forestry program by the city, there is
a $3.80 return (American Forests 2014).
Creating a successful urban forestry program requires not only collaboration on
the profession planning and development level, but must be rooted in the community.
The case studies I reviewed were based in communities that voiced support and desire for
trees within the built environment; the 2004 survey conducted by the U.S. Forest Service
Urban and Community Forestry Program reflects the social and aesthetic values of the

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urban forest to city-dwellers. The common denominator of success for these cities seems
to be the community participation and involvement in maintaining the urban forest in
partnership with local urban forestry management plans that provide a budget and
implementation strategy. With their urban forest success, Portland, New York, and
Sacramento are considered “Tree Cities”. The National Arbor Day Foundation (NADF)
qualifies “Tree Cities” with four standards: 1) Establish a governing body to oversee
forestry efforts; 2) Design, implement and enforce a tree ordinance; 3) Set a budget of at
least $2 per capita annually to urban forestry efforts; 4) Observe Arbor Day through city
proclamation.
Section 5: Comparison – Chico, CA Urban Forest Management Plans
Chico has been a “Tree City” according to NADF standards for over 30 years.
Nicknamed “the City of Trees”, Chico has continually shown its appreciation and
commitment to preserving its historic native tree species. Goal #6 of the Open Space and
Environment Element (OS-6) in the Chico 2030 General Plan is to provide a “healthy and
robust urban forest”. Policy OS-6.1 “ensures the continued protection and management of
the urban forest to reduce energy demand, increase carbon sequestration and reduce
urban heat gain.” Several actions are included under goal OS-6, such as the creation of
urban forest maintenance strategies, energy saving plans, and tree planting programs
(Action OS 6.1.1-6.1.3). Under the Sustainability Element, policy SUS-6.4 promotes the
continued support of community trees to increase carbon sequestration. Chico’s General
Plan also acknowledges the need for trees in its Community Design Element, under
Action CD-4.1.2 (Urban Forest), which promotes the protection and enhancement of the
urban forest as part of preserving the character of Chico’s diverse landscapes. Though

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the city’s General Plan includes goals for a thriving urban forest, the City of Chico Parks
Division created the Urban Forest Management Plan in 2012 to help further develop and
prioritize a successful urban canopy (Britton 2012, 6-13). The Urban Forest Management
Plan identifies historic tree species, contains tree population counts and resources, and
includes future development goals (Britton 2012, 6-13).
CONCLUSION:
Over the last twenty years, urban forest assessment techniques have developed
significantly; the U.S. Department of Agriculture Forest Service has been developing the
Urban Forest Effects (UFORE) model since the 1990s in an effort to better monitor and
study urban forest conditions, structure and functions (Wang 2013).
Modern statistical and scientific research shows that the urban forest has
undeniable benefits for the environment, economy and community. Drawbacks of
investing in urban forestry are minimal; however, maintenance costs can be a concern for
some cities that have limited financial resources. For instance, $2 per capita for a city
population of 50,000 calls for $100,000 investment, annually; whereas, $2 per person in a
more dense urban area skew the budget to be much more expensive. Since the financial
data can fluctuate depending on location and the local economy, it is important to
prioritize urban forests in environments that show the most need. For example, Los
Angeles is an urban center that has experienced urban sprawl and is located in an arid
climate; San Francisco is located in the bay, and experiences coastal winds that disperse
air pollution and aid in reducing the urban heat island effect. These two Californian cities
are urban hubs, but have very different needs, development, and density demographics. It

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is important to evaluate the environmental condition of a city against the economic
tradeoffs of the urban forest, while prioritizing community health and happiness.
Overall, the costs of planting city trees and sustainable vegetation are minor when
contrasted with the potential savings. Knowing the strategies of some of the most
successful urban forestry management plans, other municipalities can take note. With
careful attention, many potential problems associated with city trees can be mitigated. For
example, placement of street trees so they don’t obstruct important signage and
implementation of trees and plants that are generally non-allergenic are easy fixes (Lohr
2004, 28-35). Urban forestry is a growing priority for large metropolitan areas. In 2006,
the U.S. Conference of Mayors established a Community Trees Taskforce in an attempt
to increase awareness of the value of urban forests and the social, economic and
ecological benefits they can provide (Cochran 2008). With government officials
prioritizing urban forest environments, more grant funding is available. For more
information on how to enhance the urban forest in your community, visit
www.arborday.org.

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Sources:
Britton, Denice F. "Urban Forest Management Plan City of Chico." City of Chico Parks
and Recreation Department. January 1, 2012. Accessed October 25, 2014.
http://www.chico.ca.us/general_services_department/park_division/documents/ufmgtplan
draft2012_6-13.pdf.
"City of Sydney: Urban Forest Strategy 2013." February 1, 2013. Accessed October 22,
2014. http://www.cityofsydney.nsw.gov.au/.
Cochran, Tom. "Protecting and Developing the Urban Tree Canopy." Usmayors.org.
March 4, 2008. Accessed October 22, 2014.
http://usmayors.org/trees/treefinalreport2008.pdf.
Dwyer, Mark C., and Robert W. Miller. "Using GIS to Assess Urban Tree Canopy
Benefits and Surrounding Greenspace Distributions.” Journal of Arboriculture.
www.actrees.org. March 1, 1999. Accessed October 23, 2014.
Gatrell, J.d, and R.r Jensen. "Growth through Greening: Developing and Assessing
Alternative Economic Development Programmes." Applied Geography 22, no. 4 (2002):
331-50.
Lohr, Virginia. "How Urban Residents Rate and Rank the Benefits and Problems
Associated with Trees in Cities." Journal of Arboriculture 30, no. 1 (2004): 28-35.
Accessed November 5, 2014. http://joa.isa-arbor.com/.
Manning, William. "Plants in Urban Ecosystems: Essential Role of Urban Forests in
Urban Metabolism and Succession toward Sustainability." International Journal of
Sustainable Development & World Ecology 15, no. 4 (2008): 362-70.
Pothier, Aaron J., and Andrew A. Millward. "Valuing Trees on City-centre Institutional
Land: An Opportunity for Urban Forest Management." Journal of Environmental
Planning and Management: 1380-402. Accessed November 7, 2014.
Shin, Won Sop, Hon Gyo Kwon, William E. Hammitt, and Bum Soo Kim. "Urban Forest
Park Use and Psychosocial Outcomes: A Case Study in Six Cities across South Korea."
Scandinavian Journal of Forest Research: 441-47. Accessed November 7, 2014.

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"Ten Best Cities for Urban Forests." American Forests: Protecting and Restoring Forests.
January 1, 2014. Accessed October 23, 2014. www.americanforests.org.
Wang, M-Z, and J.r. Merrick. "Urban Forest Corridors in Australia: Policy, Management
and Technology." Natural Resources Forum 37, no. 3 (2013): 189-99.

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