Tropical forests play a crucial role in regulating carbon and water cycle at global scale and can dampen or amplify anthropogenic climate change through biogeochemical and/or biophysical feedbacks. However, there are signs of a weakening of the Amazonian forest carbon sink during the past three decades, as a consequence of growth-rate leveling off, concomitant with an increase in tree mortality in response to a greater climate variability. Disturbances, including droughts, are likely to become more intense and/or frequent under climate change. Dynamic global vegetation models (DGVMs) represent the exchanges between the surface and the atmosphere and are embedded in global climate models.
Results/Conclusions
Here we first evaluate and discuss mortality mechanisms implemented in a spatially aggregated (SURFEX) and a cohort based (ORCHIDEE-CAN) DGVM over the Amazon when the DGVMs are forced by observed climate. Using forest inventories and remotely sensed data, we show that both models lack the ability to account for (1) the spatial pattern of biomass and (2) mortality induced by disturbances. In light of significant progress in large-scale vegetation modeling (forest structure representation, competition) and the growing concern about tropical tree mortality under climate change, we also explore tree mortality representation, sensitivity to climate (variability and trends) and CO2 increase, and impact on climate feedbacks using the models that participated in the phase 6 of the Coupled Model Inter-Comparison Project (CMIP6). These simulations are becoming available.