Black locust is a widespread alien species, which is considered to influence natural ecosystems. However, its effects on plant species diversity in forests are still controversial. Here, we compared species composition, species diversity, phylogenetic diversity and phylogenetic structure between black locust community and native deciduous oak community dominated byQuercus acutissima orQ. variabilis, to clarify the impacts of black locust. A total of 17 black locust communities and 17 corresponding native oak communities (with plot size of 20 m×30 m for each) were selected in the hilly areas of Shandong Province, China. We measured understory plant species composition and diversity. There was no significant difference in species and phylogenetic α diversity between black locust community and native oak community. The species and phylogenetic β diversity in black locust community were lower than that in deciduous oak community. The decay rate of phylogenetic similarity was lower in black locust community than in deciduous oak community, indicating that plant species had close phylogenetic relationships in black locust communities. Black locust led to more homogenous understory communities. In addition, black locust community had higher alien species richness than native oak community. While black locust did not affect plant species richness, it changed the structure and composition of plant community. Long-term monitoring of black locust forests should be carried out to effectively control the threat from exotic plants to local ecosystems.
