Seed bank diversity and composition during natural tropical forest regeneration

Regeneration of tropical forests following agricultural abandonment is a critical process for global ecosystem restoration and climate change mitigation. Despite being a key component of tropical secondary succession, our understanding of soil seed bank dynamics remains incomplete. This study examines the soil seed bank in 10 forest stands, 10 to 130 years after abandonment, and two agricultural areas in and around the Barro Colorado Natural Monument in central Panama. Using this chronosequence that spans early to late successional stages, we investigated changes in density, species richness, dispersal mode, and composition of the soil seed bank. While early succession was dominated by herbaceous species, their density and richness declined sharply in the first decades. By 50 years, seed densities had stabilised at a lower level and were dominated by woody species, whose species richness and density increased over time. In terms of species composition, forest sites ≤ 10 years old differed significantly from sites ≥ 50 years. Seed banks of sites 50 to 130 years old were similar to each other in species composition based on abundance but not incidence, suggesting a slow recovery of rare species. Our findings also indicate the recovery of animal-dispersed seeds in older forests and that forest integrity, which reflects the condition and continuity of the surrounding forest, was more influential than forest age in driving seed bank recovery. These results emphasise the prominent role of animal seed dispersers and intact, well-connected forest patches in driving seed bank recovery and, by extension, forest regeneration.