Biodiverse cities: The nursery industry, homeowners, and neighborhood differences drive urban tree composition

In arid and semiarid regions, where few if any trees are native, city trees are largely human planted. Societal factors such as resident preferences for tree traits, nursery offerings, and neighborhood characteristics are potentially key drivers of urban tree community composition and diversity, however, they remain critically understudied. We investigated patterns of urban tree structure in residential neighborhoods of the Salt Lake Valley, Utah, combining biological variables, such as neighborhood and plant nursery tree species and trait composition, and sociological data comprised of resident surveys and U.S. Census data. We sampled nine neighborhoods that varied in household income and age of homes. We found more tree species were offered in locally owned nurseries compared with mass merchandiser stores and yard trees at private residences were more diverse than public street trees in the same neighborhoods. There were significant differences among neighborhoods in street and yard tree composition. Newer neighborhoods differed from older neighborhoods in street tree species composition and trait diversity, while neighborhoods varying in affluence differed in yard tree composition. Species richness of yard trees was positively correlated with neighborhood household income, while species richness of street trees was negatively correlated with home age of neighborhood residences. Tree traits differed across neighborhoods of varying ages, suggesting different tree availability and preferences over time. Last, there was a positive correlation between resident preferences for tree attributes and the number of trees that had those attributes both in residential yards and in nursery offerings. Strong relationships between social variables and urban tree composition provides evidence that resident preferences and nursery offerings affect patterns of biodiversity in cities across Salt Lake Valley. These findings can be applied toward efforts to increase taxonomic and functional diversity of city trees in semiarid regions in ways that will also provide ecosystem services of most interest to residents.