Impacts of the attributes of patches and the surrounding matrix on the phylogenetic diversity of tree species in urban remnant forests

Urbanization is a major cause of biotic homogenization and evolutionary poverty. Urban remnant forests are biodiversity hotspots in cities but are prone to phylogenetic homogenization. However, how urbanization-driven changes in patch attributes and landscape heterogeneity levels of the surrounding matrix affect plant phylogenetic diversity in urban remnant forests remains unclear. We quantified tree phylogenetic diversity and structure in 30 remnant forest patches in Guiyang, China, using chloroplast genome data and analyzed the effects of patch attributes and the surrounding matrix on tree phylogenetic diversity and structure in the forests while considering tree species stage. The phylogenetic diversity of saplings/seedlings was lower than that of adult trees. Small patches contributed more than large patches to the overall phylogenetic diversity of remnant forest ecosystems. Additionally, tree phylogenetic diversity was positively associated with configurational heterogeneity of the surrounding matrix, while phylogenetic diversity and relatedness were negatively related to the percentage of surrounding impervious surfaces and patch size. Accordingly, we suggest maintaining configurational heterogeneity and controlling the speed of urban expansion in the surrounding matrix to better conserve urban remnant forests. Furthermore, the preservation of small forest remnants and tree species in the sapling/seedling stage should be prioritized.