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

increase the social and economic value of an area. Economic benefits of urban forest

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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

treatment, air quality improvements, habitat installation and wildlife programs, and/or

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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

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Source: www.arborday.com

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

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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

Source: www.arborday.comWith 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

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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

Source: www.arborday.com

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

and reduction to inland temperatures are cited as main objectives in the Sydney Urban

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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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Source: www.arborday.com

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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Appendix A

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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/ufmgtplandraft2012_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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