Detecting vulnerability of humid tropical forests to multiple stressors

Humid tropical forests play a dominant role in the functioning of Earth but are under increasing threat from changes in land use and climate. How forest vulnerability varies across space and time and what level of stress forests can tolerate before facing a tipping point are poorly understood. Here, we develop a tropical forest vulnerability index (TFVI) to detect and evaluate the vulnerability of global tropical forests to threats across space and time. We show that climate change together with land-use change have slowed the recovery rate of forest carbon cycling. Temporal autocorrelation, as an indicator of this slow recovery, increases substantially for above-ground biomass, gross primary production, and evapotranspiration when climate stress reaches a critical level. Forests in the Americas exhibit extensive vulnerability to these stressors, while in Africa, forests show relative resilience to climate, and in Asia reveal more vulnerability to land use and fragmentation. TFVI can systematically track the response of tropical forests to multiple stressors and provide early-warning signals for regions undergoing critical transitions. [Display omitted] •An index to track vulnerability of global rainforests to climate and land use•Four decades of satellite data show widespread vulnerability across the tropics•Response of rainforests to heat and drying varies across the continents•Early warning from the index can identify regions for conservation and restoration Rainforests are being lost at an alarming rate due to deforestation and degradation. As these forests lose their intactness and diversity, their resilience to climate change declines and they become more vulnerable to droughts and wildfires. Here, we built a spatially explicit tropical forest vulnerability index (TFVI) based on observations of forest cover, carbon, and water fluxes to identify areas where rainforests are losing resilience to disturbance and are changing toward an irreversible state, a “tipping point.” Our findings show how and where tipping points may occur, either as a gradual downhill decline of ecosystem services or an abrupt change. We present TFVI as an index to monitor tropical forests and provide early-warning signals for regions that are in need of policies that simultaneously promote conservation and restoration to increase resilience and climate mitigation. Rainforests take hundreds of years to be formed into a diverse and complex structure that is lush but fragile. The re