Seedling recruitment in a hurricane-driven tropical forest: Light limitation, density-dependence and the spatial distribution of parent trees

Abstract

1. We used inverse modelling to parameterize spatially-explicit seedling recruitment functions for nine canopy tree species in the Luquillo Forest Dynamics Plot (LFDP), Puerto Rico. We modelled the observed spatial variation in seedling recruitment following Hurricane Georges as a function of the potential number of seedlings at a given location (based on local source trees and the potential contribution of parents from outside of the mapped area) and of light levels and density-dependent mortality during establishment. We adopted the model comparison paradigm and compared the performance of increasingly complex models against a null model that assumes uniform seedling distribution across the plot. 2. Our data supported a model in which parents must reach a threshold size before any seedling production will occur. Once parents attain that size, the relationship between tree diameter and the number of seedlings produced is fairly flat for the majority of species. These results contradict previous analyses that simply assumed a linear relationship between biomass and seedling production and a uniform size threshold for seedling production across species. 3. The majority of species tested supported models that included at least one of a bath term (contribution from non-local trees), conspecific density dependence and light availability after the hurricane. Density dependence shifted the mode of the effective dispersal kernel away from potential parent trees and significantly reduced the number of seedlings established near parent trees. Recruitment from non-local sources accounted for 6-81% of observed seedling recruitment depending upon the tree species. Light availability appeared to divide species into three groups that showed more successful seedling establishment at low (< 5% of full sun), intermediate or high light levels (> 30% full sun). 4. Differences between individual species in the importance of local vs. bath recruitment and the intensity of density dependence suggest the existence of distinct recruitment syndromes that go beyond the traditional focus of tropical tree life histories. Understanding these syndromes will provide valuable insights into the spatial distribution of tropical tree species and the maintenance of tropical forest diversity. © 2005 British Ecological Society.