The effects of local filtering processes on the structure and functioning of native plant communities in experimental urban habitats

Abstract

Despite a growing literature‐base devoted to document biodiversity patterns in cities, little is known about the processes that influence these patterns, and whether they are consistent over time. In particular, numerous studies have identified the capacity of cities to host a rich diversity of plant species. This trend, however, is driven primarily by introduced species, which comprise a large proportion of the urban species pool relative to natives. Using an experimental common garden study, we assessed the relative influence of local assembly processes (i.e., soil environmental filtering and competition from spontaneous urban species) on the taxonomic and functional diversity of native plant communities sampled over four seasons in 2016–2018. Taxonomic and functional diversity exhibited different responses to local processes, supporting the general conclusion that species‐ and trait‐based measures of biodiversity offer distinct insights into community assembly dynamics. Additionally, we found that neither soil nor competition from spontaneous urban species influenced taxonomic or functional composition of native species. Functional composition, however, did shift strongly over time and was driven by community‐weighted mean differences in both measured traits (maximum height, Hmax; specific leaf area, SLA; leaf chlorophyll a fluorescence, Chl a ) and the relative proportions of different functional groups (legumes, annual and biennial‐perennial species, C4 grasses, and forbs). By contrast, taxonomic composition only diverged between early and late seasons. Overall, our results indicate that native species are not only capable of establishing and persisting in vacant urban habitats, they can functionally respond to local filtering pressures over time. This suggests that regional dispersal limitation may be a primary factor limiting native species in urban environments. Thus, future regreening and management plans should focus on enhancing the dispersal potential of native plant species in urban environments, in order to achieve set goals for increasing native species diversity and associated ecosystem services in cities.

Plant and soil microbial community assembly processes across urban vacant lots

“…A higher proportion of spatial structure in the explained variance of species composition and SES_FDis for native plant species (Figure 3) suggested that community assembly of native species would be largely determined by dispersal limitation (Beninde et al, 2015;Borowy & Swan, 2022;Reeve et al, 2022), which supported our hypothesis (Figure 1). Because we investigated a limited number of local environmental variables, however, explained variance of species composition and functional diversity for native species could be enhanced by including environmental factors such as microclimate that can directly regulate plant establishment, growth, and environment.…”

“…Because we investigated a limited number of local environmental variables, however, explained variance of species composition and functional diversity for native species could be enhanced by including environmental factors such as microclimate that can directly regulate plant establishment, growth, and environment. Nonetheless, previous studies have suggested that native species may respond to local filtering pressures by changing their functional traits over time (Borowy & Swan, 2022), making environmental filtering less important for native species assembly than dispersal limitations. Although urban ecosystems are primarily affected by human activities such as habitat conversion and fragmentation of remaining habitats (Williams et al., 2009), our results highlight the primary importance of dispersal limitation in driving native plant species assembly in urban systems (Aronson et al., 2016; Borowy & Swan, 2022).…”

“…Nonetheless, previous studies have suggested that native species may respond to local filtering pressures by changing their functional traits over time (Borowy & Swan, 2022), making environmental filtering less important for native species assembly than dispersal limitations. Although urban ecosystems are primarily affected by human activities such as habitat conversion and fragmentation of remaining habitats (Williams et al., 2009), our results highlight the primary importance of dispersal limitation in driving native plant species assembly in urban systems (Aronson et al., 2016; Borowy & Swan, 2022).…”

“…Since native plant species are originally present in the local species pool, they have adapted to the local environment, and their spatial distributions reflect their dispersal characteristics (Avolio et al., 2021). The spatial structure of the habitat is thus expected to be a primary factor in determining the community assembly of native plant species (Figure 1; Beninde et al., 2015; Borowy & Swan, 2022; Reeve et al., 2022). In contrast, exotic plant species are invaders that subsequently arrive at the local species pool.…”