A NEIGHBORHOOD APPROACH TO THE BIOGEOGRAPHY OF PUERTO RICAN TREES

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The geographic distributions of tree species reflects both physical (e.g., geology, climate) and biological processes (e.g., competition, herbivory). These factors do not act independently. For example, the strength of competition among trees may be stronger in low fertility soils. However, only a few studies have examined the simultaneous effects of physical factors and biological processes on tree growth and survival. Such synthesis is central to predicting tree species responses to environmental change. This is a critical issue in tropical forests because these ecosystems are experiencing rapid environmental change and play a key role in regulating global climate. This research will develop a novel analytical approach to characterize the joint effects of physical heterogeneity and local biological interactions on growth and survival of tree species across the island of Puerto Rico. The island has high tree diversity, marked environmental and climate gradients, and an extensive amount of existing data, making this an ideal site for this research. Results from this study will inform the likelihood of success of several USDA Forest Service initiatives to adapt to rapid environmental change. Existing collaborations between the researchers and local organizations will facilitate a direct impact on the management and conservation of Puerto Rican forests. Data will be made available online and provided directly to local management agencies, including the US Forest Service and the Puerto Rico Department of Natural Resources. The researchers also will organize workshops on the analytical methods at Puerto Rican institutions. Finally, the project will train and employ a Puerto Rican technician and a postdoctoral researcher, contributing to STEM workforce development.Range dynamics and community assembly reflect the interactive effects of regional environmental heterogeneity and local processes. Yet empirical examination of these interactions is rare. The researchers will develop a novel functional trait-based, spatially-explicit neighborhood approach to disentangle local effects of environmental heterogeneity and biotic interactions on tree growth and survival across Puerto Rico while accounting for individual trait variation. To do so, they will couple (a) tree trait measurements across species ranges traits, including traits related to water use strategies, (b) trait-based neighborhood models of tree growth and survival derived from data collected in 24 mapped plots, and (c) generalized joint attribute models that characterize species distributions with respect to regional environmental gradients using herbaria collections. They will test the following hypotheses: (1) the negative effect of local biotic interactions on tree growth and survival is highest at the most environmentally favorable sites for a species, fostering regional coexistence; (2) the spatial structure of intraspecific trait variation across environmental gradients fosters such coexistence. Results from this research will empirically examine the importance of individual trait variation in mediating regional species coexistence and test the importance of a stabilizing mechanism in promoting species-coexistence and diversity in tropical forests. The research will lay a conceptual foundation for future studies that place local community interactions within a biogeographic context and transform understanding of the environmental and biotic factors that mediate forest community assembly at regional scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.