Geographical Distribution Pattern of Species Diversity of the Genus Salix L. and Its Relationship with Climate in China

The geographical distribution of the species diversity of the genus Salix L. in China is studied using the geographical information system and spatial statistics. The relationship between the Salix L. species diversity pattern and climate is analyzed using (stepwise) generalized linear regression analysis. The results show that:1) The genus Salix L. species is predominantly extensive on the regional scale and clustered on the local scale. The aggregation areas are located in northeastern and southwestern China and some areas of Altay Diqu in Xinjiang. 2) The diversity center of the Salix L. species is located in the adjacent area of the southwestern Qinghai-Tibetan Plateau and southern Hengduan Mountains in the latitudinal and longitudinal bands of (25°N-35°N, 95°E-105°E), with 19 sections including 173 species, accounting for more than 60% of the total in China. 3) The species richness of the Salix L. is the greatest, affected by single factor where the amount of energy or moisture is respectively optimized, and decreases as the amount of energy and moisture moves above or below the optimal condition. 4) Given the combined effect of energy and moisture, climate accounted for 44% (adjusted R²; P < 0.0001) of the Salix L. species diversity variation, and moisture is the dominant factor. Species diversity of Salix L. increases as the amount of moisture increases and the regression coefficient of mean annual precipitation is 0.66. The conclusion of this study partly supports the water-energy dynamic hypothesis and niche conservative hypothesis. However, the cause of the species diversity pattern of Salix L. species cannot be completely explained by any single hypothesis, which indicates that other factors like historical factors, terrain heterogeneity, soil factors or disturbances etc. are also important factors in shaping the diversity pattern of Salix L. species.