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Benefits of Urban Forests

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1. 1 Shady Cities as Part of Sustainable Development: Benefits of the Urban Forest By Kelly Murphy 2. 2 Kelly Murphy November 13, 2014 Shady Cities as part of Sustainable…
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  • 1. 1 Shady Cities as Part of Sustainable Development: Benefits of the Urban Forest By Kelly Murphy
  • 2. 2 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
  • 3. 3 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
  • 4. 4 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
  • 5. 5 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
  • 6. 6 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
  • 7. 7 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
  • 8. 8 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
  • 9. 9 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 Source: www.arborday.com
  • 10. 10 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 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
  • 11. 11 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
  • 12. 12 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
  • 13. 13 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
  • 14. 14 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
  • 15. 15 is important to
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