COS 46-4 - Biotic homogenization in parklands and vacant lots in a shrinking city

Abstract: Urbanization is thought to be a major driver of biotic homogenization, or an increase in the similarity in biological communities. Similar types of disturbances likely favor similar species, and developed and urbanized areas are generally more homogenized. The urban matrix can be a complex mix of disturbed and less disturbed areas, and impacts of this on the diversity patterns is unclear. Here we investigated the extent of homogenization at different levels of urbanization in parklands, as well as areas recovering from recent disturbances (vacant lots) in Cleveland, Ohio. In shrinking cities like Cleveland, vacant lots represent a large portion of the green space present, followed by parklands. We quantified the plant and soil microbial communities at different levels of urbanization to determine the extent of homogenization. We surveyed vacant lots, as well as utilized existing parkland plant community datasets from the Cleveland Metroparks, and examined soil microbial samples, to assess plant and soil microbial community alpha and beta diversity. We hypothesized that urban sites would exhibit less floral and microbial β diversity than rural sites, with intermediate levels in suburban sites. We further hypothesized that vacant lots, with a more recent history of human impacts, were likely more homogenized.





In parklands, spatial turnover in plants was significantly greater in exurban sites than in urban sites (F_2,8 = 5.18, P = 0.036). Additionally, the mean increase in native plant richness over a five-year period was significantly greater in exurban sites relative to suburban sites (P = 0.032), indicating that the rate at which parklands gain native species may be affected by urbanization. Bacterial communities were not significantly different by urbanization level intensity, nor were fungal communities. In vacant lots, while alpha diversity was higher in exurban areas for plants, fungal alpha diversity was lower. Plant and bacterial communities did not differ significantly in beta diversity by urbanization level, but fungal communities were more homogenized in urban vacant lots. Our findings suggest that the degree of homogenization varies considerably by land use type, and that plant and microbial communities may respond differentially to urbanization.