Successional, spatial, and seasonal changes in seed rain in the Atlantic forest of southern Bahia, Brazil

Seed arrival is a limiting factor for the regeneration of diverse tropical forests and may be an important mechanism that drives patterns of tree species' distribution. Here we quantify spatial and seasonal variation in seed rain of secondary forests in southern Bahia, Brazil. We also examine whether secondary forest age enhances seed dispersal and whether seed rain density and diversity in secondary forests decay with distance from mature forest. Across a chronosequence of 15 pairs of mature and secondary forests, 105 seed traps were installed and monitored for one year. We tested the effects of secondary forest age, distance from mature forest, and seasonality on monthly seed rain density, diversity, seed dispersal mode, and diaspore size. We found that secondary forest age had strong, positive effects on the diversity of seed rain, which was generally higher during the wet season. Moreover, contrasting patterns among diversity indices revealed that seeds of rare species occurred more often in 40 yr old secondary forests and mature forests. While the proportion of biotically and abiotically dispersed seeds did not change significantly with distance from mature forest across all forest age classes, we found that biotically dispersed seeds contributed disproportionately more to seed rain diversity. Our results emphasize the importance of biotic dispersal to enhance diversity during secondary succession and suggest that changes in secondary forest structure have the potential to enhance the diversity of tropical secondary forests, principally by increasing dispersal of rare species.