Urbanization strengthens the edge effects on species diversity and composition of woody plants in remnant forests

Background: Urban remnant forests are embedded in urban areas and are threatened directly and indirectly by urbanization. The direct effects(e.g., loss of area) have been well studied. However, knowledge about the indirect influence of urbanization through edge effects on the biodiversity in remnant forests is limited.Methods: In this study, we surveyed woody plant species in 72 plots in nine remnant forest patches in Guiyang,China. We examined the influences of urbanization and edge effects on the species diversity and composition of woody plants in remnant forests. We compared alpha diversities and quantified compositional dissimilarities in interior and edge sites at different levels of urbanization. We also measured the niche width of the recorded plant species and assessed whether high levels of urbanization and edge effects increased the number of generalist species.Results and conclusions: The Shannon index, the Simpson index and the Pielou index of adult trees were lowest in the edge habitat under high levels of urbanization. Significant differences in the Shannon index and the Simpson index of sapling/seedling were detected between interior and edge sites under low urbanization. The edge effects on the species composition of adult trees were intensified by high levels of urbanization. Woody plant species with wide niche widths were more abundant at edge sites under high levels of urbanization. Therefore, we recommend that urban expansion surrounding remnant patches should be strictly controlled to alleviate edge effects on biodiversity.