Spatiotemporal patterns of urban tree canopy and environmental equity in Atlanta

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Koo, Bon Woo
Botchwey, Nisha
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With growing concerns about climate change, the benefits of urban tree canopy has gained a significant attention, leading to various efforts aimed at increasing urban tree canopy. Because urban tree canopy is often considered as environmental amenity, past studies in the field of environmental equity have established that urban tree canopy is unevenly distributed across the socioeconomic spectrum, favoring those with higher socioeconomic status who can outbid others. An increase in urban tree canopy can attract higher socioeconomic classes, allowing the neighborhood-sorting to occur in a longitudinal manner. Many of the past studies used cross-sectional models to examine the relationship between the distribution of urban tree canopy and socioeconomic status of residents, and the understanding of the longitudinal relationship has been limited. In addition to the environmental equity, this study adds the vulnerability theory into the research framework. In vulnerability theory, human vulnerability is defined as a function of exposure, adaptive capacity, and sensitivity. The urban trees are known to be effective risk moderator, and socioeconomic/demographic indicators have been frequently used as proxies of adaptive capacity and sensitivity, together providing a pathway to bridge the uneven distribution of urban tree canopy and their benefits to the vulnerability theory. Based on this research framework, this study examines the longitudinal relationship between residential tree canopy and socioeconomic status in Atlanta between 2000 and 2013. Using census data and two remote sensing datasets, two cross-sectional spatial regression models are developed for 2000 and 2013, and one longitudinal spatial regression for the period of 2000 to 2009. The findings suggest that in 2000, socioeconomic indicators used in environmental equity and vulnerability, such as the proportion of racial minority and poverty rate, generally supported the existence of inequity in Atlanta. The longitudinal model between 2000 and 2009, however, indicates improvements for some of these indicators. Most notably, the higher percentage of African-American and Asian population in 2000 and an increase in poverty rate is associated with an increase in residential urban tree canopy. An increase in the percentage of residents with bachelor’s degree or higher is associated with a decrease in residential tree canopy. There is an interaction effect between the change in the percentage of African-American and the change in the poverty rate. The 2013 cross-sectional model shows that the higher proportions of African-American and Asian are associated with higher tree canopy. However, economic disadvantages – the poverty rate and the proportion of renters – remains as significant predictors of environmental inequity. This study illustrates the importance of a longitudinal perspective in better understanding the relationship between urban tree canopy and socioeconomic status. Policy suggestions aimed at providing urban tree canopy in more equitable ways and reducing the vulnerability gaps are made.
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