COS 294-4 - Tree Health Depends on Local Site Characteristics and Patterns of Urban Displacement in Chicago’s West Side

Abstract: Tree health is essential for ecosystem services in cities; however, most literature focuses on patterns of tree canopy cover. Here, we explore major contextual indicators of urban tree health. While the legacy of redlining in U.S. urban tree canopies has been well studied, the added impacts of recent urban displacements are less established. Gentrification affects the built environment (e.g. construction and retrofitting) and the social landscape (e.g. displacement, community disruption) and could therefore impact tree health through damage, shifts in species composition, or changes to relationships between communities and greenspaces. Simultaneously, small-scale site conditions and management (i.e. mulching) are known to impact tree health but are not studied across neighborhoods. Using field data of 700 street trees in the west sides of Chicago (summers of 2021-22), we ask 1) how local-scale growing conditions impact tree health across multiple neighborhoods and 2) if tree health varies across areas in different stages of gentrification. For question 1, the best model for tree health included conditions like tree size, tree species, the presence of mulch and other forms of resident intervention, and the presence of power lines. We found that the model fit varied greatly depending on which metric of tree health we used (r2 ranging from 0.067 to 0.415) but that improperly placed mulch was consistently correlated with lower tree health, and signs of resident interaction with the trees were correlated with less crown stress. Larger tree size tended to correlate with lower tree health, though tree health varied by species with trees that had been classified as appropriate for urban areas generally having lower crown stress. Looking then at differences across levels of gentrification, for question 2, differences were visible primarily for two of four tree health metrics: leaf discoloration and crown stress. Areas actively undergoing gentrification generally had a smaller proportion of their trees with low stress (40%) and low discoloration (32%) than areas that were near a university (58%, 69%), had already been gentrified (51%, 57%). Gentrifying areas had similar proportions of trees with low crown stress to areas susceptible to gentrification (40% vs 42%) but not for discoloration (32% vs 58%). Our results indicate that small-scale growing conditions and management decisions (like mulching and tree species selection) are important across neighborhoods and that there are differences in tree health that map onto patterns of gentrification, though it depends on the health metric.