Patterns of species and phylogenetic diversity of Pinus tabuliformis forests in the eastern Loess Plateau, China

Pinus tabuliformis forests are major components of temperature coniferous forests in North China. These forests harbor a remarkable richness of both animal and plant taxa while providing multiple goods and services. However, the species distribution patterns and the underlying mechanisms of community assembly for P. tabuliformis forests are still not very well understood. We analyzed the distribution patterns, construction, and main drivers of P. tabuliformis forests based on 113 forest plots (20 m × 30 m) in the mountain areas of Shanxi, in the eastern Loess Plateau, China. Our findings indicated the plant flora composition was rich, but significantly different among different mountain areas. A total of 357 species belonging to 227 genera, 71 families, 36 orders, 4 classes, and 3 phyla were recorded in the 113 plots. The species richness (SR) and phylogenetic diversity (PD) of the natural forests were higher than that of the artificial forests. The main influence factors of PD and the net relatedness index (NRI) were the natural environment, and then forest type and forest structure, and the relative roles were different for woody and herbaceous species in the different areas. Overall, the primary environmental drivers of PD were topographic conditions, including slope and slope position, followed by total phosphorus and water factors. The topographic and soil variables had primary impacts on the PD and NRI patterns on Mount Luliang, while climate and soil variables had strong independent effects on PD and NRI patterns on Mount Taihang. In addition, the differences in forest type and structure had strong effects in determining PD and NRI patterns in the plant community. The tendency of increasing phylogenetic clustering along the temperature gradient indicated that environmental filtering played an important role in community assembly at a broad scale. The differences of PD and NRI between artificial and natural forests indicated that forest origin, microhabitat, and interspecific competition played an important role in the PD and NRI patterns at a local scale. Our results indicated that conservation projects have been effective for conservation and restoration of the P. tabuliformis forests. However, some problems still need to be addressed in afforestation, management, and exploitation.