| Successional patterns of structure and composition are increasingly well understood in tropical secondary forests, yet little is known of how underlying recruitment processes act to generate divergent successional trajectories. In general, the processes that limit secondary forest composition to a highly site-specific subset of mature forest taxa have been widely theorized but are rarely empirically tested. This information is of critical importance to restoration objectives, as effective strategies will be designed to counteract natural limitations to forest succession. Using a fully-crossed factorial experiment, I tested the effects of source population proximity, seed availability, understory competition, and predator access on patterns of mature forest seedling recruitment (stem and species density, diversity, and composition) over ∼2.5 annual cycles in a 10--12 year-old secondary forest of the Ecuadorian Choco. I also examined dispersal limitation and employed several auxiliary methods to elucidate stage-specific dynamics from seed to seedling. I found that recruitment constraints operated almost exclusively at the seed stage via dispersal limitations and predation pressures, while understory competition and mature forest distance were not limiting factors. Seed rain dynamics were driven by the contrasting roles of dispersal-limiting mature forest proximity and distance-mitigating neighborhood remnant trees, with the key difference in comparison to mature forest pattern being reduced local species density and stand-level diversity. These limitations were largely mitigated via seed additions, the benefits of which overshadowed the limiting influence of predation and generated highly significant increases in both the stem and species density of mature forest seedlings. In the absence of seed additions, mature forest colonists appeared to come from locally available mature forest trees, 'reshuffled' within the secondary forest stand by dispersers. My findings suggest that recruitment niches in secondary forest are largely unoccupied, and that mature forest taxa are well-adapted to fill them provided they arrive. |
