Urban Forestry and Stormwater Management: Investigating the Benefit and Health of Urban Trees in Green Infrastructure Installations

Bioretention is a green infrastructure practice commonly implemented to manage urban stormwater worldwide. While studies have described the many benefits trees provide to urban areas, including improved air quality, wildlife habitat creation, and heat island mitigation, knowledge of their contributions to stormwater management in bioretention is limited. There is a need to characterize tree health in bioretention and the performance benefits they provide to inform appropriate plant selection and maximize the functionality of these systems. In response, several studies were implemented to investigate the role of trees in bioretention practices.The health of trees in existing bioretention practices was compared to urban trees in the southeastern United States. Using crown condition to measure overall tree health, health differences were linked to dissimilarities between bioretention conditions and species-specific site preferences. The environmental factors influencing tree health in bioretention were investigated using random forest models, which identified parameters relating to media composition and chemistry, along with species selection and planting location. Results indicated that tree health may be improved in bioretention if species selection is guided by media analysis and species compatibility with bioretention growing conditions is considered.The contributions of various tree species in bioretention were investigated in a mesocosm-scale study. Differences in pollutant uptake between species were not significant, indicating the role of bioretention media in pollutant removal. Evapotranspiration from treed mesocosms was significantly higher than nonvegetated mesocosms, highlighting the role of transpiration in the systems. Results suggested that trees contribute to bioretention hydrology and that significant differences among species, which were attributed to growth rate, exist.Two bioretention suspended pavement systems were installed and monitored over 27-months. Significant runoff volume reductions were observed at both practices. Influent suspended solids were significantly reduced at the underdrained practice, though other influent pollutant removal was not significant. Tree transpiration from the systems increased with greater water availability. Regression models indicated that transpiration was influenced by vapor pressure deficit and that stomatal regulation of water losses were occurring in water-limited conditions. Findings demonstrated the viability of suspended pavement systems in stormwater management applications and illustrated how design parameters influence transpiration within these practices.