112 Cowett: Methodology for Spatial Analysis of Municipal Street Tree Benefits Arboriculture & Urban Forestry 2014. 40(2): 112–118 Methodology for Spatial Analysis of Municipal Street Tree Benefits F.D. Cowett Abstract. Street trees comprise a fraction of the urban forest; however, due to their public function, the benefits they pro- vide to urban residents have received particular attention from researchers. Spatial analyses of street tree benefits have been based on street tree counts that do not account for differences in tree species and size that in turn impact leaf surface area from which most benefits are derived. The United States Forest Service’s i-Tree Streets soſtware program quantifies street tree ben- efits and does account for differences in tree species and size, but is not a Geographic Information Systems program and does not facilitate the spatial analysis of street tree benefits. This paper proposes a methodology for analyzing the spatial distribu- tion of street tree benefits employing measures based on i-Tree Streets. Providence, Rhode Island, U.S., serves as a case study. Key Words. Benefits; GIS; i-Tree; Services; Spatial Analysis; Street Trees. Research has shown urban trees to provide benefits to urban residents. These benefits include but are not limited to improved air quality (Cavanagh et al. 2009), mitigation of heat island effect (Lynn et al. 2009), increased real estate values (Anderson and Cordell 1988), stormwater reduction (Xiao et al. 1998), a greater sense of community (Kuo 2003), and encouragement of physical activity (Giles-Corti and Donovan 2003). Because of these benefits, the spatial distribution of urban trees is of interest. For example, researchers have examined whether urban trees are distributed evenly in urban areas, and if not, whether an uneven distribution is associated with socioeconomic factors, such as income, education, and race. In most of these studies, tree canopy cover was selected as the dependent variable. This choice made sense because many benefits provided by trees, particu- larly those associated with ecosystem services, are proportional to leaf surface area (McPherson and Rowntree 1989), while canopy cover, the percentage of ground area covered by the vertical projection of tree crowns (Jennings et al. 1999), is a mea- sure related to leaf surface area. Thus, Talarcheck (1990), Iverson and Cook (2000), Escobedo et al. (2006), Luck et al. (2009), and Pham et al. (2012) ©2014 International Society of Arboriculture found a positive relationship between wealth and canopy cover; Heynen et al. (2006), Luck et al. (2009), Flocks et al. (2011), and Zhou and Kim (2013) found a negative relationship between canopy cover and minority populations; Heynen and Lindsey (2003) found increased canopy cover associated with higher levels of educational attainment and older housing stock; and Donovan et al. (2011) found increased canopy cover within 50 m of a house to be associated with improved birth outcomes for non-Hispanic white women. Street trees (i.e., trees growing in a street right- of-way) represent a minority of the overall urban forest (Dwyer et al. 2000). However, because of their public function—they are generally planned and managed by municipalities and are typically the urban trees with which most urban residents have the most frequent contact—street trees have oſten received particular attention (Cumming et al. 2008). In studying the spatial distribution of street trees, researchers have employed various metrics. In Tampa, Florida, U.S., Landry and Chakraborty (2009) differentiated street tree canopy cover from urban forest canopy cover and found less street tree canopy cover to be correlated with higher proportions of African-American residents, lower
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