Drivers of tree survival in an evergreen-deciduous broadleaf karst forest in southwest China

Understanding tree mortality and the underlying driving mechanisms is essential for understanding forest dynamics and tree species coexistence. Based on survival data from two censuses of a large (25-ha) fully mapped subtropical karst forest plot, the present study quantified the simultaneous effects of tree size, soil, topography, and neighborhoods on tree mortality at three levels (community, guild, and species). Our study suggested that tree size, biotic neighborhood, and abiotic factors influenced tree survival, but the relative importance of these mechanisms for tree mortality differed greatly among species guilds. Of the variables tested, tree size was the most important driver of tree survival, and had a strong negative relationship with tree mortality, while abiotic variables and neighborhood effects were of secondary importance. Regarding abiotic factors, both soil and topography affected tree survival. Abiotic factors generally influenced the survival of common trees, smaller individuals, and slow growing, shade-tolerant understory species. Regarding biotic factors, the biotic neighborhood effects may be irrelevant for tree survival under these conditions, as indicated by the results of both conspecific neighbor density and heterospecific neighbor density analyses. These results suggested that it is necessary to simultaneously consider the relative importance of intrinsic (tree size) and extrinsic (biotic and abiotic) factors on forest dynamics to better understand, conserve, and manage subtropical karst forests.