Urban green space provides refuges for species that are unintentionally introduced by humans and which do not belong to the remnants of natural habitats in urban areas. However, the quantitative relationships between urban green space properties and these spontaneous species are unclear. To address this, we surveyed plant species occurring in urban green patches in Kunming city, which is located in a biodiversity hotspot in southwest China. We classified spontaneous plants into native, non-native and invasive plant species. A total of 386 spontaneous species belonging to 278 genera and 92 families were recorded in 190 patches. Most of the recorded species were herbaceous plants (76.2 %). While invasive species constituted a relatively small proportion of the total species pool (17.9 %), six out of ten of the most frequently occurring species were invasive. Regression models inspired by the theory of Island Biogeography show that total, native, non-native and invasive spontaneous species richness in urban green patches were best explained by the size of the ‘island’ (patch area), dispersal limitations (as expressed by ‘distance to city boundary’) and edge effects (as shown by the landscape shape index). While the set of drivers of spontaneous plants is similar for the different groups of species, the relative importance of each driver varies among them. Our study provides quantification of drivers of biodiversity patterns in urban green space. Based on this understanding, planning and management of urban green space can be adapted to maximize spontaneous plant conservation in rapidly urbanizing biodiversity hotspot regions.
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