Response of Humid Tropical Forests to Emerging Stressors

Humid tropical forests (HTFs) contain the largest reservoirs of global vegetation carbon and serve as the most biologically diverse terrestrial ecosystems. Although these ecosystems are historically adapted to some level of disturbance, they are now facing persistent stresses from land-use and climate changes, impacting their functions and environmental services. We use time series of ground and satellite observations (2000-2018) to develop standardized stress and response indices that quantify changes of tropical forest across spatial and temporal scales. This novel pantropical approach improves our understanding the impacts of stressors on processes that control ecological and biological responses of HTFs. We describe the forest stressors from components of land-use activities including deforestation, degradation and fire, to climatic factors such as excessive warming, atmospheric drying and declining rainfall patterns. Results indicate contrasting effects and highly heterogeneous spatial and temporal patterns of climate and land-use stressors. We show that, although forests are exposed to comparable intensity of stress from land-use and climate change since 2000, the responses in terms of carbon stocks, carbon and water fluxes, and biodiversity demonstrate different degrees of resilience and vulnerability. With increasing stress from hotter and dryer climate, our approach allows detection of early-warning signals for how and where tropical forests are approaching a critical threshold.