SG: Synergistic effects of forest fragmentation and droughts on tropical plant demography

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Droughts have many negative effects on species in forest ecosystems, including increased risk of population decline and even extinction. It has been hypothesized that the effects of drought are especially severe for populations found in the fragments of habitat that remain following deforestation. This is thought to be especially true for plant species in biodiversity rich tropical forests, which are often especially sensitive to changes in environmental conditions. The research team will use a long-term dataset on plant growth, reproduction, and mortality collected in the Central Amazon to determine how droughts influence the risk of plant extinction in rain forest fragments. In addition to answering an important unresolved ecological question, the results will help those tasked with managing biologically, socially, and economically critical forest ecosystems for a future in which droughts are predicted to become more frequent or intense. In doing so the investigators will be training early-career scientists in advanced statistics and mathematical modeling, making several ecologically valuable datasets publicly available, and curating an art museum exhibit about rain forests and their global importance to society. To determine how droughts and deforestation interact to increase the risk that plant populations will go extinct, the researchers will use previously collected data on the growth, reproduction, and mortality of thousands of individuals of a plant species from the central Amazon: the understory herb Heliconia acmuniata. These data were collected in both unbroken rain forest and experimentally isolated forest fragments near the city of Manaus, Brazil. The researchers will first use four decades of data on rainfall in the region to identify drought years and categorize drought intensity. They will then compare plant growth, reproduction, and mortality before and after droughts, as well as how long after droughts any differences can be detected. Finally, these statistical analyses, along with the analysis of drought frequency, will be used to calibrate mathematical models with which they will simulate future population sizes under alternative drought scenarios predicted for the Amazon. The results of these simulations will indicate if the probability that populations will go extinct because of drought is greater in unbroken rain forest or forest fragments, and if this probability changes when droughts are more frequent or severe.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.