4501 Circle 75 Parkway Suite f-6320 Atlanta, ga 30339 (770) 953-4143 Table of Contents
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- Executive Summary
- Introduction
- Urban Ecological Analysis Methods
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Jeff De Witt, GIS Technician, Pacific Meridian Resources, 4501 Circle 75 Parkway, Suite F-6320, Atlanta, GA 30067, (770) 953-4143, e-mail: jdewitt@pacificmeridian.com Eric Fowler, Macon City Forester, Macon-Bibb County Parks and Recreation Department, P.O. Box 247, Macon, GA 31202, (912) 751-7693. Kass Green, President, Pacific Meridian Resources, 5915 Hollis Street, Building B, Emeryville, CA 94608, (510) 654-6980.
Funds for this project were provided by the Urban and Community Forestry Grant Assistance Program administered through the Georgia Forestry Commission.Executive SummaryPacific Meridian Resources was contracted by the City of Macon to conduct an Urban Ecological Analysis that would quantify the benefits produced by the area’s urban forests. The findings of this analysis are intended to provide public officials, policymakers, and city planners with a better understanding of the value of trees and their role in the urban environment. The City of Macon has seen considerable growth and development during the past decade. This growth has had a significant impact on Macon and Bibb County’s urban forest lands, resulting in net loss of approximately 4000 acres of vegetation from 1985 to 1997, including almost 500 acres of forest land. The loss of urban forest lands often leads to higher summer temperatures in urban areas, poor air quality, and increased stormwater runoff and soil erosion. Trees help to alleviate these problems by lowering heating and cooling costs, decreasing air pollution, and reducing stormwater runoff and erosion. Real dollar values can be assigned to these types of urban forest benefits with a process called Urban Ecological Analysis - a way to map, measure, and calculate the value of the urban forest ecosystem. This analysis combines low-level aerial photographs, urban forest analysis software, called CITYgreen, and real-world data from several study sites throughout the region to assess the economic and environmental benefits of urban trees. Data collected at each study site included detailed information of tree, building, grass land, and impervious surface characteristics. Data from all of the study sites was entered into the CITYgreen software for analysis. Urban forest benefits analyzed include forest health, energy savings, air quality, and stormwater management. Results from this analysis for the six study sites selected include the following: Forest health – average tree health rating was midway between fair and good. Trees having the best health were found in areas that had been newly developed. Trees in highly developed areas with large amounts of impervious surfaces had the lowest health rating. Energy savings – existing tree canopy cover saved homeowners from $16 to $69 in summer cooling costs in residential areas, with an average of about $38 per home. The greatest savings were found in the study site with the highest tree canopy percentage, although high tree canopy percentages did not always correlate to significant energy savings. Air quality – trees in all study sites produced approximately $1200 in annual pollution removal benefits. The existing trees in all the sites also store over 235 tons of carbon, sequestering about 1300 pounds of carbon per year. The estimated value of the sequestered carbon for all study areas is approximately $616 per year. Sites that had the most biomass (trees and other vegetation) had the greatest air quality benefits. Stormwater management – the existing tree canopy of all the study sites reduced the volume of stormwater runoff by an average of 23 percent when compared to areas with no tree cover. Similarly, the peak flow rates (velocity) were also reduced by an average of 29 percent for all sites when compared to land with no trees. Sites having the very little vegetation and large amounts of impervious surfaces had the highest runoff volumes and peak flow rates. Projecting these results across the total area of Macon and Bibb County indicates that the existing urban forest lands in Macon save the city and its residents over $2.7 million annually, an average of $256 per acre for commercial and residential areas. Trees in the commercial and residential areas of Bibb County produce almost $7.5 million per year in savings, an average of almost $300 per acre. Based on the acres of vegetation lost from 1993 to 1997, the City of Macon lost over $9,000 in urban forest benefits during this period. The savings lost by Bibb County totaled approximately $105,000 from the loss of almost 650 acres of vegetation from 1993 to 1997. The findings for Bibb County include the total area of Macon. The results of this study indicate that the area’s existing urban forest lands provide substantial energy savings, air quality benefits, and stormwater management advantages to the residents of Macon and Bibb County. The energy savings findings indicate that trees can significantly reduce a homeowner’s summer cooling costs. The area’s urban forests also help to improve air quality by removing and storing substantial amounts of pollutants from the atmosphere, including the green house gas carbon dioxide. The results of the stormwater analysis demonstrated that the loss of vegetation significantly increases the volume and velocity of stormwater runoff. Trees and other vegetation retain large amounts of water and decrease the rate at which stormwater travels, reducing soil erosion and minimizing the impact of flooding. The benefits quantified in this project can be used when evaluating the role urban trees should play in the area’s overall urban landscape. As a result, public officials, developers, and planners will be able to better assess the economic value of trees when making decisions about their region’s future growth and development. IntroductionLike many other metropolitan areas across the country, the City of Macon is facing the problem of urban sprawl. Macon’s population base has steadily grown during the past decade (U.S. Census Bureau 1999), with most of this growth occurring in areas surrounding the city. The growth and development in urban areas like Macon can have a considerable impact on a city’s urban forest lands, often resulting in a significant loss of trees and other vegetation. A 1998 study found that the City of Macon and Bibb County sustained a net loss of approximately 4000 acres of vegetation from 1985 to 1997, including almost 500 acres of forest land (Pacific Meridian Resources 1998). The loss of urban forest lands can negatively impact an urban environment by creating summer temperatures that are higher in urban areas than in the surrounding countryside, concentrating air pollution problems into urban areas, and increasing stormwater runoff and soil erosion (USDA Forest Service 1990). Trees can help to alleviate these problems. Studies have shown that urban trees help to lower heating and cooling costs, decrease air pollution, conserve water, and reduce stormwater runoff and soil erosion (USDA Forest Service 1990, McPherson et al. 1994). Although the benefits of trees have been widely recognized, it has been difficult to put these benefits into real dollar figures. Without a method to quantify the benefits of urban trees, city officials and planners lack valuable information they need in order to make informed decisions about their city’s urban forest resources. In response to this problem, American Forests, a non-profit forestry conservation organization, developed a way to map, measure, and calculate the value of the urban forest ecosystem with a process called Urban Ecological Analysis. This analysis combines low-level aerial photographs, urban forest analysis software, called CITYgreen, and the most up-to-date scientific research to calculate the economic and environmental benefits of urban trees. In March 2000, the City of Macon contracted Pacific Meridian Resources to conduct an analysis of Macon’s urban forest lands. Pacific Meridian Resources utilized the CITYgreen software to quantify the benefits of Macon’s urban forest resources. The findings of this analysis are intended to provide public officials, policymakers, and city planners with a better understanding of the value of trees and their role in the urban environment. Urban Ecological Analysis MethodsSelection of Study SitesThe Urban Ecological Analysis method is based on the selection of sample sites chosen to best represent the ecological and land use characteristics of a particular city (American Forests 1996). As the vegetation cover characteristics of each sample site (study site) are unique, the various study sites will provide a good representation of the differing economic and ecological benefits common to the area. As in traditional forest sampling, this type of urban forest sampling allows us to make inferences about the condition of the urban forest across a larger area. Black and white low-level aerial photographs (1993 one-meter Digital Orthographic Quarter Quadrangles) were used to examine and select possible study sites. For this project, six study sites were selected throughout the City of Macon and Bibb County. Each study site chosen was approximately the size of one city block, about five acres.
As Table 1 indicates, all of the study sites were located in either residential or commercial areas. These two land use types represent over 60 percent of the total area within the City of Macon. Several attempts were made to establish a study site in an industrial land use area. Unfortunately, sites on industrial land were inaccessible. Figure 1. – Location of Urban Ecological Study Sites 
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