Several mechanisms have been proposed to explain the high number of species present in tropical forests. The outcome of these processes, which could include random or non-random elements, may be reflected in the evolutionary history and distribution of functional traits (plant size, leaf size, flowering pattern, etc.) in a community. Because they reflect "community assembly in action", successional tropical forests (developing after a disturbance) provide an ideal natural laboratory for testing the power of an integrated multi-faceted approach to community assembly. Using data collected in secondary and mature forests in Costa Rica and Puerto Rico, the proposed research will develop a novel approach to understanding community assembly that will integrate detailed forest inventory data. This approach will be used to assess the relative importance of habitat differences, niche differences, and lack of seedlings in driving tropical forest community assembly at different spatial scales and across life history stages. Coordinated data collection will allow for comparisons of functional traits across successional stages within a context of the plants' evolutionary history, which will be reconstructed using DNA bar-coding technology.
The major objectives of this research are to (1) compare patterns of species-level phylogenetic (evolutionary) relationships and functional similarity of plants between successional and mature forest communities; (2) link functional traits and phylogenetic structure with population and community dynamics through sophisticated models of tree mortality and growth, and (3) assess the role of recruitment limitation and the relative importance of functional and phylogenetic relatedness in predicting species- and stage-specific population dynamics during succession.
Secondary forests now cover more area than remaining old-growth forests in many tropical countries and are increasingly important components of tropical landscapes for biodiversity conservation and provision of ecosystem services. A mechanistic understanding of how these forest communities are assembled is urgently needed. The evolutionary relationships among plants that will be discovered as part of this project will contribute to a deepening understanding of the angiosperm evolutionary history. Two doctoral graduate students, one postdoctoral researcher, and undergraduate students from the University of Puerto Rico, the largest Hispanic institution in the US federal system, will be trained.
The proportion of tropical forests worldwide that are disturbed is rising rapidly to the point where they are becoming dominant components of the tropical landscape making them an important carbon sink. Understanding the recovery and regeneration of these landscapes is therefore critical for our ability to manage them and project their fate. Recent developments in community ecology have suggested that incorporating functional and phylogenetic information into modern analytical frameworks may lead to a more predictive ecology. Specifically, knowing what species and where they come from provides a substantial advantage over simply knowing the names of the species one is studying and trying to model. In this research program we asked whether predictable deterministic interactions on very localized scales or stochastic events play a relatively larger role during the succession of tropical forests. To address this issue we employed detailed functional trait and phylogenetic information for trees in Puerto Rico and Costa Rica. This information was used in neighborhood models and co-existence analyses to query whether functionally and phylogenetically similar neighbors positively or negatively influence individual performance and community structure or play no role at all. The results generally have shown that the functional identity of neighbors plays a large role in determining performance and coexistence and therefore the successional trajectory of disturbed tropical forests. The phylongenetic information, on the other hand, was somewhat less informative indicating traits important for determining forest succession have weak, though significant, phylogenetic signal. In sum, the work has shown that management and predictions of the fate of disturbed tropical forests are greatly enhanced by functional trait information pertaining to individuals and species. The award resulted in the training and promotion of three female students. One PhD student and one undergraduate student were trained at Michigan State University in field identification of tropical tree seedlings, functional trait measurement and community ecology. One PhD student was training in functional trait ecology at the University of Connecticut and conducted field research in Costa Rica. One postdoctoral research was trained in hierarchical modeling at Columbia University. The award produced a photographic field guide for the trees of the El Yunque National Forest in Puerto Rico freely available via the Field Museum's Rapid Field Guide website. The results from the research conducted can be directly used to guide management policies for the increasingly large areas of disturbed tropical forests worldwide that provide a valuable carbon sink.
