Environmental and spatial contributions to tree community assembly across life stages and scales in evergreen-deciduous broadleaf karst forests, southwest China

Spatial and environmental processes are two ecological processes that have attracted considerable attention in plant community assembly, depending on sampling scale and life history. However, the processes that determine community assembly have not been studied in the karst region of southwest China. In this study, a 25-ha (500 m x 500 m) monitoring plot within the subtropical climax forest in the karst region was established and canonical correspondence analysis was used to reveal the effects of topography and soil on the spatial patterns of tree community assembly. Our study suggests that spatial processes dominate species composition and the combined effects of spatial and environmental processes play an important role. Overall interpretation rate increases with enlarging the sampling scale. However, the pattern of variation partitioning was similar in different life stages. Environmental variables significantly affected species composition at different sampling sizes and life histories and had a higher interpretation rate of species composition on larger sampling sizes. Topographic wetness index was the most important variable to explain species composition of the environmental variables. These results suggest that it is necessary to consider the relative importance of environmental and spatial factors on community assembly to better understand, conserve, and manage subtropical karst forests.