Studies of forest dynamics plots (FDPs) have revealed a variety of negative density-dependent (NDD) demographic interactions, especially among conspecific trees. These interactions can affect growth rate, recruitment and mortality, and they play a central role in the maintenance of species diversity in these complex ecosystems. Here we use an equal area annulus (EAA) point-pattern method to comprehensively analyze data from two tropical FDPs, Barro Colorado Island in Panama and Sinharaja in Sri Lanka.
View Article and Find Full Text PDFInteractions among neighboring individuals influence plant performance and should create spatial patterns in local community structure. In order to assess the role of large trees in generating spatial patterns in local species richness, we used the individual species-area relationship (ISAR) to evaluate the species richness of trees of different size classes (and dead trees) in circular neighborhoods with varying radius around large trees of different focal species. To reveal signals of species interactions, we compared the ISAR function of the individuals of focal species with that of randomly selected nearby locations.
View Article and Find Full Text PDFLong-term surveys of entire communities of species are needed to measure fluctuations in natural populations and elucidate the mechanisms driving population dynamics and community assembly. We analysed changes in abundance of over 4000 tree species in 12 forests across the world over periods of 6-28 years. Abundance fluctuations in all forests are large and consistent with population dynamics models in which temporal environmental variance plays a central role.
View Article and Find Full Text PDFNiche and neutral theories emphasize different processes that contribute to the maintenance of species diversity and should leave different spatial structures in species assemblages. In this study we used variation partitioning in combination with distance-based Moran's eigenvector maps and habitat variables to determine the relative importance of the effects of pure habitat, pure spatial, and spatially structured habitat processes on the spatial distribution of tree species composition and richness in a 25-ha tropical rain forest of Sinharaja/Sri Lanka. We analyzed the contribution of those components at three spatial scales (10 m, 20 m, and 50 m) for all trees and the three life stages: recruits, juveniles, and adults.
View Article and Find Full Text PDF