This research is to determine the variability of nutrient supply to trees in tropical forests, and its causes. Although most tropical forests are considered nutrient poor, there is evidence that erosion can increase the supply of nutrients by exposing new, nutrient rich rock to weathering. In Hawaii, this effect can be pronounced and trees on slopes are often much bigger, with higher nutrient concentrations, than trees on uneroded surfaces. As a result, there is as much variation in fertility across a small section of tropical forest on the old island of Kauai as there is on uneroded surfaces across the entire Hawaiian Islands. Despite the importance of these results for understanding Hawaiian forests, it is not clear how good a proxy Hawaii is for continental forests. To clarify this question, we are quantifying nutrient variability across a lowland tropical forest in Costa Rica. Comparing these systems will shed light both on the applicability of the Hawaiian model to the continental tropics and the extent of nutrient variability across tropical landscapes. The answer has broad implications for both scientists and policy makers, because spatial variation in nutrient supply affects species distributions, carbon storage, and the sustainability of agriculture.
