Baltimore Ecosystem Study Institute of Ecosystem Studies

2017 BES Annual Meeting Presentation and Poster Abstracts

Linking community assembly processes and patterns in experimental urban vacant lot habitats
Borowy, Dorothy
Co-Authors: Chris Swan

Abstract: Background/Question/Methods Urbanization induces dramatic land-use changes, which are often reflected in unique biodiversity patterns. Urban habitats, for example, have been found to support high proportions of introduced ‘urban exploiters’ in exchange for native species. Although this trend has been observed in many cities, leading to the characterization of urban communities as globally homogenized, there still lacks a general understanding of the processes responsible for shaping these patterns. We conducted an experimental common garden study designed to identify the relative influence of local assembly processes (i.e., environmental filtering and competition) on native plant communities assembling in urban habitats. The main purpose was to identify which factors limit the representation of native plant species in urban vacant lot habitats, with the broader aim of using this information to guide future city planning efforts that are focused on enhancing biodiversity in abandoned urban green spaces. Native communities consisting of 10 species, representing a variety of functional strategies, were seeded in 2m x 2m plots filled with either topsoil or subsoil fill material used in vacant lot demolition projects. Additionally, a weeding treatment (weeded vs. unweeded) was used to isolate interspecific competition from urban plant species that either recruited into the plots from the surrounding region or were present in the soil seed bank. Species and functional trait data were collected seasonally during peak biomass in October 2016 and during peak plant growth in June 2017. Native plant community responses to treatments were assessed via mixed-effects models and permutational multivariate ANOVA (PERMANOVA) tests on native species richness, Shannon-Weaver diversity, and species and functional composition data. Results/Conclusions Patterns in native species diversity and composition differed between the two sampling seasons. Results showed that taxonomic measures (i.e., native species composition and Shannon-Weaver diversity) did not appreciably change in response to soil environmental- or competition-based filtering processes in either sampling season. Functional trait measures, however, showed distinct patterns between sampling seasons. Specifically, native species height and SLA measures were significantly influenced by soil type in the first season, indicating strong soil environmental filtering effects on functional patterns in the early stages of community establishment. Local effects also became more prominent over time as competition-based filtering was also shown to influenced native species height and SLA by the second season. These results broadly suggest that although native plant species are able to establish and survive in experimental vacant lot habitats, urban assembly processes play a key role in influencing community-level functional trait patterns over time.