Disentangling the effects of topography and space on the distributions of dominant species in a subtropical forest

Topography and space are two important factors determining plant species assemblages in forest communities.Quantification of the contribution of these two factors in determining species distribution helps us to evaluate their relative importance in determining species assemblages.This study aims to disentangle the effect of topography and space on the distributions of 14 dominant species in a subtropical mixed forest.Spearman correlation analysis and the torustranslation test were used to test the species–habitat associations.Variation partitioning was used to quantify the relative contributions of topography and space at three sampling scales and three life stages.Correlation analyses and torus-translation tests showed species abundance was mostly correlated with topographic wetness index,vertical distance from the channel network and convexity.Variation partitioning showed that pure topography,pure space and spatially structured topography explained about 2.1 %,41.2 % and 13.8 %of the variation in species distributions,respectively.For nine species,total topography fractions peaked in 20 m quadrats.For ten species,the pure space fractions peaked in 50 m quadrats.For many species,the total topography fraction andthe pure space fraction were larger for the most abundant life stages,which reflected the importance of sampling effect.However,some cases did not follow this trend suggesting that the effects of ecological processes such as habitat filtering,density dependence or dispersal limitation may exceed the sampling effects.In conclusion,we found that spatially structured topography and pure space primarily shaped the distribution of dominant tree species.Furthermore,their effects were both scale- and life stage-dependent.