Patterns of species diversity and its determinants in a temperate deciduous broad-leaved forest

Biodiversity conservation has long been a subject of extreme interest to community ecologists, with a particular focus on exploring the underlying causes of species diversity based on niche and neutral theories. This study aims to identify the potential determinants of species diversity in a deciduous broad-leaved forest in the transitional region from subtropical to temperate climate in China. We collected woody plant data and environmental variables in a fully mapped 25-ha permanent forest plot, partitioned the beta-diversity into local contributions (LCBD) and species contributions (SCBD), and then applied multivariate linear regression analysis to test the effects of biotic and abiotic factors on alpha-diversity, LCBD, and SCBD. We used variation partitioning in combination with environmental variables and spatial distance to determine the contribution of environment-related variations versus spatial variations. Our results showed that the indices of alpha-diversity (i.e., species abundance and richness) were positively correlated with soil available phosphorus (P) and negatively with slope. For the beta-diversity, environment and space together explained nearly half of the variations in community composition. Approximately 60% of the variation of LCBD in the understory layer, 40% in the substory layer, and 29% in the canopy layer were jointly explained by topographic, soil and biological variables, with biotic factors playing a dominant role in determining the beta-diversity. Species abundance accounted for a large proportion of the variations in SCBD in each vertical stratum, and niche position (NP) was the ecological trait that significantly affected the variations in SCBD in the substory and canopy layers. Our findings help to gain better understanding on how species diversity in forest ecosystem responds to environmental conditions and how it is influenced by biotic factors and ecological traits of species.