Changes in phylogenetic structure and species composition of woody plant communities across an elevational gradient in the southern Taihang Mountains, China

Understanding community assembly mechanisms along the geographical gradients is of great importance in ecological research. The Taihang Mountains are the intersection of the north and south flora, with abundant species and complex community structures, which provide multiple services. However, the phylogenetic community structure and composition of woody plants in the south Taihang Mountains are still not very well understood. In this study, 35 forest dynamic plots were established along the natural forest distribution areas from 850 to 1850 m above sea level. We explored the pattern of elevational change in the phylogenetic structure and composition of woody species communities and influencing factors using regression analysis, correlation analysis, and principal coordinate analysis. Our results displayed that both the net relatedness (NRI) and nearest taxon (NTI) values at most of the plots were within random confidence intervals (-1.96 to 1.96). Meanwhile, a significant negative correlation existed between the phylogenetic community structure and the elevational gradient (NRI: r = -0.61, p < 0.05; NTI: r = -0.57, p < 0.05). That is, with the elevation increasing, the phylogenetic community structure tended to be overdispersed. Furthermore, the phylogenetic community structure was only significantly affected by soil total nitrogen (p < 0.05) using multi-stepwise regression analysis. Above all, these illustrated that the assemblages of woody plant communities were mainly influenced by the neutral process and environmental filtering. The results of PCPS displayed that high-abundance rosids plants and asterids plants contributed greatly to the phylogenetic community structure in this region and no significant differences were found in phylogenetic community composition in different elevation areas using the Wilcoxon test (p > 0.05). In summary, our findings reveal the community assembly mechanism of woody plants along an elevation gradient in a local scale and help to gain a better understanding of how species diversity or species composition in the forest ecosystem responds to environmental conditions and it is useful for biodiversity maintenance in the southern Taihang Mountains.