Species richness patterns and the determinants of larch forests in China.

Larch forests are important for species diversity, as well as soil and water conservation in mountain regions. In this study, we determined large-scale patterns of species richness in larch forests and identified the factors that drive these patterns. We found that larch forest species richness was high in southern China and low in northern China, and that patterns of species richness along an elevational gradient depend on larch forest type. In addition, we found that patterns of species richness in larch forests are best explained by contemporary climatic factors. Specifically, mean annual temperature and annual potential evapotranspiration were the most important factors for species richness of tree and shrub layers, while mean temperature of the coldest quarter and anomaly of annual precipitation from the Last Glacial Maximum to the present were the most important for that of herb layer and the whole community. Community structural factors, especially stand density, are also associated with the species richness of larch forests. Our findings that species richness in China's larch forests is mainly affected by energy availability and cold conditions support the ambient energy hypothesis and the freezing tolerance hypothesis.