Beyond canopy cover: Examining predictors of urban forest composition and diversity across California

Link To Share This Poster: https://cdmcd.co/WkzLgZ

Joanna P. Solins, Bogumila Backiel and Mary L. Cadenasso, Department of Plant Sciences, University of California, Davis, Davis, CA, Marvin Browne, Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA, Stephanie Pincetl, Erik Porse and Julia Skrovan, Institute of the Environment and Sustainability, UCLA, Los Angeles, CA, Erik Porse, Office of Water Programs, Sacramento State University, Sacramento, CA, Lawren Sack, Department of Ecology & Evolutionary Biology, University of California Los Angeles, Los Angeles, CA

Background/Question/Methods
The distribution of urban tree canopy has been widely studied as an environmental justice concern, and numerous studies have shown that canopy cover in urban neighborhoods corresponds to the affluence of their populations. However, total canopy cover is not the only important consideration: the composition and diversity of urban forests also influence the services and disservices urban trees provide. For instance, tree species differ in their provision of cooling, habitat, and food; their demand for water and maintenance; and their production of allergens and litter. Diversity also influences the urban forest’s vulnerability to stress and disturbance over time. Predictors of composition and diversity are thus key considerations for understanding the equity of urban forest distribution. We used 59 municipal tree inventories from cities across California to examine relationships between the composition and diversity of public urban forests and a variety of urban characteristics. Using ordination techniques, we first determined the importance of climate in explaining species composition, and then examined the explanatory power of sociodemographic and development factors while controlling for climate differences. Using linear models, we assessed relationships between diversity (Shannon index) and explanatory variables. We conducted these analyses at both the city scale and the census tract scale.
Results/Conclusions
The composition of urban forests across California cities was strongly related to climate, and city-scale composition was also significantly related to median household income, racial diversity, and ethnicity. At the census tract scale, urban forest composition was related to several sociodemographic factors, including income, racial diversity, ethnicity, and home ownership, as well as to the age of development. Species diversity tended to be greater in larger cities, and was also positively related to median household income at the city scale. At the census tract scale, diversity was most strongly predicted by the age of development, with more recently developed areas typically having less diversity. Our analysis demonstrates that variation in urban forest composition and diversity is tied to sociodemographic and development characteristics, both within and among cities, highlighting the importance of species-level data for better understanding patterns of urban forest distribution. Future analyses that connect compositional variation to differences in the provision of ecosystem services and disservices, as well as vulnerabilities in the face of changing climate conditions and water resources, can inform management and policy decisions that promote equity in the distribution of urban forest benefits beyond canopy cover.