Forest productivity and drought in tropical Africa: observations from the Global Ozone Monitoring Experiment-2

Abstract:

The impact of seasonal water stress on Africa’s tropical regions has yet to be characterized despite drought’s potential to cause famine and a reduction of biodiversity across the continent. Through the analysis of a new data set of sun-induced chlorophyll fluorescence (SIF) from the Global Ozone Monitoring Experiment-2, we demonstrate that fluorescence varies with water availability, particularly over regions with distinctive wet and dry seasons. Water availability was determined via both precipitation (from the Global Precipitation Climatology Project) and daytime canopy water content measurements (from the SeaWinds Scatterometer onboard the QuickSCAT satellite). Variance in SIF values was largely explained by both canopy water content and precipitation, which paralleled one-another. When viewed in the context of the previously defined relationship between fluorescence and gross primary production (GPP) – SIF scales linearly with GPP – our results suggest that photosynthetic activity in tropical Africa is limited by water availability. The characterization of this trend is critical in defining the response of tropical ecosystems to water stress and corroborating similar relationships in other tropical regions (e.g. Amazonia). Ultimately, the viability of Africa’s tropical regions amidst a changing climate is rooted in its ecosystem-wide response to water stress; the future of the African tropics is limited by how well plants cope with water stress.