A major challenge in ecology is to understand the mechanisms that determine the number and relative abundance of plant species in natural communities. This challenge is particularly extreme in wet tropical forests, which harbor the highest species diversity of any ecosystem globally. All plants ultimately start life as a seedling, a phase that is especially sensitive to pathogens and to the availability of light, nutrients, and water. Seedlings are a critical stage, one that impresses a signature on the species composition of forests, from the understory to the canopy. Plants, and especially trees, can live for much longer than humans and the dynamics of forests play out over even longer times scales, necessitating long-term data to capture important events that would be missed by short-term studies (e.g., seed production may occur every 12 years for some species). This proposal will extend a ~7 year record of seedling surveys in five forest stands in Costa Rica, with the goal of developing forest models based upon how seedlings of different species grow and survive in response to light, soil fertility, and natural enemies. A better understanding of the factors that govern the relative abundance of tree species is not merely an academic exercise but is critical to predict forest responses to human influences, including the deposition of nitrogen, sulfur, and other chemical pollutants from the atmosphere. Furthermore, in tropical areas, exotic tree species of known regeneration requirements often are used for reforestation because potentially-useful native species are not well known, a knowledge gap that this research will help remedy. Research results and data will be shared with the public and other scientists through a project website.
