Climate and Biodiversity Effects on Standing Biomass in Puerto Rican Forests

Carbon sequestration is a major ecosystem service provided by tropical forests. Especially in light of global climate change, understanding the drivers of forest productivity is of critical importance. Although abiotic conditions (e.g., precipitation) are known to influence forest productivity, ecological theory predicts that biodiversity may also have independent effects on productivity. We estimated standing aboveground biomass (AGB) in mature forests of Puerto Rico that span a strong precipitation gradient and 2 general soil types. With these data, we examined the independent and interactive effects of precipitation and 5 metrics of tree diversity (species richness, phylogenetic diversity, and three aspects of functional diversity) on spatial variation of AGB in forests on 2 soil types. Precipitation had a strong positive effect on AGB on both soil types, and we did not find evidence for an independent effect of diversity on AGB in either soil type. We found some evidence from plots on limestone soils that the increase in AGB along the precipitation gradient was less pronounced in plots where species richness was relatively high. We discuss our results in light of spatial scale and biodiversity–ecosystem function theory.