Lianas exhibit stronger conspecific negative density dependence than trees on tropical seedling survival

Conspecific negative density dependence (CNDD) strongly influences plant demography, especially in highly diverse tropical forests, but its relative importance may vary between growth forms. We used hierarchical Bayesian models to assess how neighbor densities affected the survival of more than 30,000 seedlings from 87 tree and 56 liana species in a tropical forest across two 1-year census intervals. Although standardized CNDD coefficients were similar between lianas and trees, lianas showed a four- to sixfold stronger per capita CNDD on seedling survival compared to trees. Specifically, adding a single conspecific neighbor (2 cm dbh at 1 m distance) reduced liana survival by -1.2% to -1.8%, whereas it only reduced tree survival by 0.3%. Nevertheless, trees exhibited greater inter-annual variation in CNDD prevalence (47%-11% of species with significant CNDD) compared to lianas (13%-23%). These contrasting patterns likely reflect growth form-specific ecological strategies in density-dependent responses to inter-annual environmental fluctuations. Our findings highlight the importance of examining per capita neighborhood effects when assessing CNDD strength and suggest that lianas and trees may utilize different mechanisms driving CNDD and exhibit varying stability in their contribution to diversity maintenance in tropical forests.