Soil nutrients, canopy gaps and topography affect liana distribution in a tropical seasonal rain forest in southwestern China

Questions Lianas are a conspicuous element of tropical forests but have largely been ignored in species-level vegetation surveys. As a result, there is limited understanding of how environmental factors structure liana communities. Location A 20-ha forest dynamics plot in Xishuangbanna National Nature Reserve, southwestern China. Methods We evaluated the distribution of the 50 most abundant liana species, comprising >18,000 individuals, in the 20-ha forest plot. Ordination analysis and generalized linear mixed models were used to evaluate how species distribution and abundance are associated with soil pH, soil phosphorus (P), soil nitrogen (N), and soil potassium (K), canopy gaps and topography. We calculated the average weighted distribution as a proxy for the optimum resource condition for each species. Results The first two axes of a canonical correspondence analysis explained 65% of the variation in liana species composition, with pH and P being the strongest drivers and highly correlated with each other. We modelled the responses of liana species to soil nutrients, and found a negative, unimodal or positive response of liana abundance with increasing soil nutrient concentrations. Forty-six of the 50 species occurred under significantly higher or lower soil nutrient conditions than expected at random. Lianas mainly separated along the P gradient, whereas for N and K most liana species tended to occupy locations with high nutrient concentrations. Conclusions Although lianas are thought to be notoriously light-demanding, soil conditions were stronger drivers of liana species distribution than gaps. Species differences in distributions were mainly driven by soil gradients in pH and P, highlighting the importance of soil nutrient status for liana niche partitioning in wet tropical forests on highly weathered soils. Most liana species had high resource requirements for N, K and light, which come along with their fast growth and acquisitive resource use strategy. Hence, below-ground resource availability plays an important role in shaping the assembly of liana communities.