Regional effects of plant diversity and biotic homogenization in urban greenspace – The case of university campuses across China

The human introduction and spread of species in urban greenspace may lead to an increase in the similarity of plant species composition between distant areas. Univervsity campuses are an important element of greenspace in many cities, but we know little about the extent to which such biotic homogenization of plant species can be detected across different regions and plant growth forms. Here, we collected plant species occurrence data from 253 Chinese university campuses in 130 cities to explore patterns and drivers of plant diversity and biotic homogenizations across different geographical regions and growth forms. We found that native species richness was positively correlated to campus area at the national scale, while non-native species richness was significantly associated with mean annual temperature, precipitation seasonality, campus area and campus age. We found limited support for homogenization caused by non-native plants in most regions. For growth forms, tree species exhibited significant biotic homogenization at the national scale, with weak or no effect for shrubs or herbs. Plant compositional similarity varied among regions, and eastern China always had the highest similarity in species composition with other regions. Combined effects of mean annual temperature and geographic distance overshadowed the roles of other predictors in shaping compositional dissimilarity in most regions. These findings suggest that multi-region settings and plant growth forms should be considered in urban biodiversity management, with special attention towards avoiding homogenization in trees. Increasing native species with local characteristics and considering region-specific environmental and socio-economic conditions are beneficial to mitigate biotic homogenization in urban greenspace.