Toward an improved understanding of tropical forest carbon cycle feedbacks in the Earth's climate system

There are large uncertainties regarding the response of tropical forest carbon cycling to expected global changes over the 21st Century. Whether tropical forests continue to act as large carbon sinks, or shift to become significant carbon sources, plays a major role in determining the rate and intensity of climate change impacts. Most terrestrial models predict a large current tropical forest carbon sink due to the effects of rising atmospheric CO2 on plant productivity. Yet the strength of this sink is likely limited by multiple factors, and the magnitudes of these constraints remain in question. As atmospheric CO2 levels continue to rise, nutrient limitations are likely to become more prominent, yet the current suite of Earth system models (ESMs) have inadequate representations of nutrient constraints on tropical forest productivity. Concurrently, the negative effects of rising temperatures and shifting precipitation patterns on plant production are expected to become more pronounced, likely driving reductions in tropical forest carbon assimilation and storage. In addition to these carbon-climate feedbacks, human land-use activities in the tropics result in both carbon sources from deforestation, and carbon sinks in secondary forests, both of which are also inadequately represented in ESMs. This talk will focus on recent advances in our understanding of these key carbon cycle processes, and explore several field research activities needed to advance ESM treatment of the underlying mechanisms.