Assessing macro-scale patterns in urban tree canopy and inequality

Urban forests provide a variety of ecosystem services that influence environmental and social welfare, but variable distribution of urban tree canopy (UTC) within and among urban areas can lead to inequitable provisioning of these benefits. Variation in UTC among and within urban areas is associated with local development patterns and socio-economic factors as well as broad-scale variation in the biophysical and socio-cultural context of urban regions. The objective of this study was to evaluate regional and continental trends in UTC distribution within and among urban areas, including assessing relationships of UTC and UTC inequality with socioeconomic/demographic factors and characteristics of urban regions. Remotely-sensed UTC assessments and US Census data were used to derive census block group-level UTC-related response variables (e.g., percent UTC, inequality in UTC) and socio-economic/demographic predictor variables (e.g., median income, population density) for forty U.S. cities spanning several biophysical and socio-cultural regions. Multiple regression analysis was used to analyze relationships of UTC with socio-economic/demographic predictor variables and the strength of these relationships was compared among cities across regions. There was a significant negative relationship (R-2 = 0.45) between total UTC and UTC inequality across the 40 cities, as the equality of UTC distribution within cities increased with decreasing total UTC. There was significant variation across biophysical and socio-cultural regions in UTC, UTC inequality, and the strength of the correlation of fine scale UTC with socio-economic/demographic factors. These findings illustrate the important role of broad-scale biophysical and socio-cultural factors as drivers of UTC patterns within and among cities.