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

Abstract

Abstract. 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.

Contribution of non‐native plants to the phylogenetic homogenization of U.S. yard floras

“…In this regard, a majority of trees in the southwestern U.S. urban areas were shown to be non‐native (Nowak , Avolio et al. ) because the original vegetation prior to urbanization was predominantly shrubland. Pincetl et al.…”

“…, Avolio et al. ; Table ). It has been suggested that traits related to overall plant size, such as plant height and larger growth forms (usually perennial), can influence aesthetic preferences.…”

Spatiotemporal variability in water sources of urban soils and trees in the semiarid, irrigated Salt Lake Valley

“…The valley was originally mainly composed of shrublands and is now dominated by non-native vegetation in cultivated landscapes (Avolio, Pataki, Trammell, & Endter-Wada, 2018), resulting in a substantial alteration in vegetation composition and structure that has to be sustained with irrigation. Despite receiving one of the lowest annual rainfall rates in the country, Utah uses the most water per capita in the United States as end-user consumption, and 60% of residential water is used outdoors (DWR, 2015).…”

Assessing methods for comparing species diversity from disparate data sources: the case of urban and peri‐urban forests

“…Previous urban ecology studies that test the hypothesis of ecological homogenization have used Jaccard's index (McKinney 2006), Sørensen's index (Pearse et al 2018 (Yang et al 2017, Avolio et al 2018, and a variety of qualitative methods, as well as specifically designed protocols which have included data on herbaceous vegetation and soils (Groffman et al 2014). Our study, which further incorporated disparate data sources, demonstrates that the Raup-Crick dissimilarity indices, based on presence/absence data, are robust to sampling differences.…”

“…However, traditional multivariate analysis methods, such as MANOVA, make stringent assumptions which are untenable for most ecological datasets (McArdle and Anderson 2001). More recently, permutational analysis of variance (PERMANOVA; Anderson 2001) has been used to compare urban forests composition across geographic and urbanization gradients (Blood et al 2016, Yang et al 2017, as well as to test for differences among neighborhood species compositions within an urban region (Avolio et al 2018). Thus, non-parametric methods are preferable.…”