Arboriculture & Urban Forestry 42(3): May 2016 sagging of the bridge span is the stress response. For humans, the stress response, especially when chronic, may have negative health consequences. In this report, the authors sought to understand the relationship between urban trees and neighbor- hood stress. The focus is on neighborhood trees, both private and public, as opposed to parks and commu- nity spaces. It is hypothesized that the quantity of trees, will have a negative correlation with the level of neighborhood stress and that lower neighbor- hood stress will be confirmed by better self-reported health and sense of safety. To address this issue, a survey of residents in neighborhoods in Wilming- ton, Delaware, U.S., was completed from autumn 2013 to spring 2014 (n = 803, with a response rate of 41%) (Figure 1). The data was aggregated to the block level (n = 80) for the analysis, and additional block level variables were added to the data set. This report summarizes the results of this research. METHODOLOGY The Study Was Conducted in Wilmington, Delaware Wilmington is located in the northeastern part of Delaware, along the Christina River and close to the Delaware River and Delaware Bay. It is the largest city in Delaware, with a population of 70,851 (U.S. Census Bureau 2010). The city encompasses 28.23 km2 2,510 people per km2 with a population density of approximately , which is comparable to nearby larger cities of Philadelphia, Pennsylvania, and Bal- timore, Maryland, U.S. The city has a large African- American population of 58% (much higher than the 21.4% for Delaware as a whole) and 32,820 housing units. Wilmington was chosen as the study area because of practical reasons and also because it provided a good opportunity to examine the main hypotheses. The lead author is familiar with the city and its neighborhoods and had a good work- ing relationship with tree organizations and local government. This familiarity was critical in the in- ventory and tree count data collection for the study. Wilmington Has a Troubled Racial History The city was occupied by the Delaware National Guard for twenty months aſter 147 comparison to other mid-sized cities, in 2012, “It topped the list in terms of violent crime, out- ranking 233 other cities for this dubious honor, with 1,703 violent crimes per 100,000 residents” (Nelson 2014). With its polarized racial mix and high crime rate, Wilmington was an ideal lo- cation to research the effect of trees on stress. The Data for This Study Came from Four Main Sources The first source for this study was a physical in- ventory conducted by the lead author, which comprised a visit to each block to conduct a block inventory and tree count. The lead author also used Google Earth™ satellite data to calcu- late tree canopy for each block. A third source of information was a secondary data source for median income and block residences. The fourth source was an individual survey instrument, which was later aggregated to block level mea- surements. Each source is discussed hereaſter. Criteria for Included Blocks For this project, three hundred blocks in Wilm- ington were selected for their uniform size and their visually observed residential nature using the Google Earth mapping service ver- sion 7.1.2.2041 (Google Earth 2013) and Mi- crosoft Bing® (Bing Maps 2014). Tree canopy coverage ranged from 0% to 100%. Commer- cial districts, irregular shaped blocks, river- banks, and freeway entrances were avoided. Using a cross-reference directory, it was possible to determine the number of inhab- ited dwellings on each of the three hundred the assassina- tion of Dr. Martin Luther King, Jr. in 1968. In blocks. From the selection of 300 blocks, 150 were chosen that had an adult population of at least 20 residents and no major commer- cial properties. The selection of 150 blocks was then plotted on a large map of Wilming- ton to visually check that all city neighbor- hoods were represented (map not shown). From this sampling frame, eighty blocks were randomly identified. Before the survey was mailed, the criterion was set that in order for a block to be included in the analysis at least five usable surveys had to be returned. With a mean of 25 eligible adults per block, this rep- resents, at a minimum, a 20% response rate. ©2016 International Society of Arboriculture
May 2016
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