Interspecific variation in seedling responses to seed limitation and habitat conditions for 14 Neotropical woody species

1. We assessed the relative importance of dispersal and niche processes in structuring plant populations at the seedling stage for 14 woody plant species (12 trees and 2 lianas) in an old-growth tropical forest of French Guiana. 2. We combined long-term data from a network of 160 stations, each comprising a seed trap and two to three neighbouring seedling plots, with fine-scale quantification of environmental variables. 3. For each species, we quantified seed limitation as the proportion of seed traps that were not reached by seeds, and establishment limitation as the proportion of stations where seeds arrived but where seedlings did not occur. All species showed strong seed limitation, whereas only one species showed significant establishment limitation. 4. We determined the proportion of variance in local seedling density explained by either seed density or environmental factors, and we assessed the effect of environment on seedling survival. 5. Although seeds showed considerable spatial clumping in all species, seed density explained a significant fraction of the variance in seedling density for only five species. Habitat preferences explained a significant fraction of the variance in seedling density for six species. Of the remaining species, four showed no significant relationship with either seed arrival or habitat conditions. 6. Environmental effects on local seedling abundance were weakly related to those on seedling survival. When seedling density was significantly correlated with a given environmental factor, survival was usually not correlated with that factor. Habitat association patterns might change over time, as environmental filtering operates. 7. Synthesis. Our results show that both seed arrival and habitat preferences contribute to explaining the abundance of tropical woody species at the seedling stage, but their relative importance showed important interspecific differences. Although our study was limited to a subset of woody species, they accounted for 27% of the individuals composing the seedling layer. Thus, our findings are likely to have important consequences in the structuring of the seedling community.