Small-scale heterogeneity in urban ecosystems shapes plant community biodiversity: a case study in Southern Italy

Urban ecosystems exhibit a high degree of spatial heterogeneity because of the complex interactions among the different elements of the urban landscape. For instance, impervious surfaces and various kinds of construction, together with the activities they serve, tend to cause landscape fragmentation and edge effects even at small spatial scales, with potential implications for biodiversity. This is especially concerning in urban green areas, where the combined effects of landscape configuration and management can crucially affect ecological dynamics and the functioning of the urban ecosystem. The present research aims at filling this gap by focusing on the small-scale landscape configuration and the management of green areas as drivers for the structural and functional biodiversity of the herbaceous plant communities. Briefly, the study was conducted in two areas in Southern Italy, subjected to similar Mediterranean climate but different management strategies in terms of mowing, fertilization and irrigation. The structural and functional biodiversity of plant communities in both the areas was investigated through three transects of phytosociological relevées, performed at different distances from the sidewalk surrounding the areas to evaluate the edge effect. The structural biodiversity was investigated by identifying taxa at the species level and estimating their abundance using the cover as a proxy, measured through the Braun-Blanquet scale, whereas the functional diversity was investigated by means of the Raunkiaer biological forms, chorology and the family to which species belong. Results show that the distance from the sidewalk plays a major role in shaping vegetation biodiversity. Where vegetation is subjected to occasional mowing and absence of anthropogenic fertilization/irrigation, patches close to the sidewalk are mainly characterized by opportunist species, in contrast to the species with longer life cycles colonizing the inner parts of the area. Conversely, where vegetation is subjected to frequent mowing such variations in functional traits are not clearly observable, and opportunist species, especially alien and cosmopolitan chorotypes, tend to dominate irrespective of the distance from the sidewalk. Findings shed light on the role of small-scale spatial heterogeneity in shaping vegetation communities in complex urban ecosystems, with potential implications in terms of management, species conservation and preservation of ecosystem functioning.