Comparison of seed rain and seed limitation between community understory and gaps in a subtropical evergreen forest

Treefall gaps have been identified as important sites for plant recruitment. In this study, we compared seed rain between forest gaps and forest interior using 150 seed traps in the understory and 19 traps in gaps in a 24 ha permanent plot of subtropical evergreen broad-leaved forest in East China. We asked how total seed abundance and seed species richness, the relative representation of different dispersal modes, and seed limitation and its components differed between canopy gaps and the understory. Results showed that most of the species found in both the understory and in gaps were animal-dispersal, but most of the seed rain was comprised of wind-dispersed species in both habitats. No significant differences in either density or diversity of seeds between gaps and non-gap sites were found. Contrary to expectations, wind-dispersed seeds did not occur significantly more in treefall gaps than in the forest understory. There were also no significant differences in seed limitation and its components (source limitation, dispersal limitation) between the understory and gaps. Seed limitation was strong for all but a few of the best-dispersed species in both gap and understory seed traps. Source and dispersal limitation showed large inter-specific variation in both the understory and in gaps. Overall, our results indicate that: (i) gaps may play a neutral role in maintaining seed diversity in this subtropical forest; (ii) under strong seed limitation both in gaps and in the understory, population and community dynamics slows and ecological drift in species composition may become a more important determinant of community structure.

► Community-wide comparison of seed limitation between gaps and understory in subtropical forests.
► The empirical evidence on whether gaps contribute to seed diversity and abundance.
► The results support the hypothesis that gaps play a neutral role in maintaining seed diversity.