IBL Tropical Forest Research Program Canopy Foliar Nutrients Our group is also taking advantage of a natural soil fertility gradient on the Osa Peninsula to test the theoretical connections between tree foliar chemistry and soil fertility. We are using sites on both nutrient-rich alluvial Mollisols and nutrient-poor Ultisols throughout the region to investigate how the foliar chemistry of mature canopy trees in lowland tropical rain forests reflects variations in soil nutrient availability. To answer this question, we are using tree climbing techniques to access the canopies of mature trees, sample foliage, and assess differences in foliar chemistry in species common on all of our sites (e.g., Brosimum utile). Our data show that while foliar nutrient content does reflect soil nutrient availability for at least some elements, within site species and seasonal variations in foliar chemistry are often as large as those across large gradients in soil nutrient levels. These data suggest the importance of species diversity in regulating soil nutrient availability through time, and provide the basis for a future, larger scale effort investigating the role of species diversity in regulating biogeochemical cycling in this diverse tropical rain forest.