Deforestation Increases Vegetation Vulnerability to Drought Across Biomes

Land use and land cover changes have altered terrestrial ecosystem carbon storage, but their impacts on ecosystem sensitivity to drought and temperature fluctuations have not been evaluated spatially over the globe. We estimate drought and temperature sensitivities of ecosystems using vegetation greenness from satellite observations and vegetation biomass from dynamic global vegetation model (DGVM) simulations. Using a space‐for‐time substitution with satellite data, we first illustrate the effects of vegetation cover changes on drought and temperature sensitivity and compare them with the effects estimated from DGVMs. We also compare simulations forced by scenarios with and without land cover changes to estimate the historical land cover change effects. Satellite data and vegetation models both show that converting forests to grasslands results in a more negative or decreased positive sensitivity of vegetation greenness or biomass to drought. Significant variability exists among models for other types of land cover transitions. We identify substantial effects of historical land cover changes on drought sensitivity from model simulations with a generally positive direction globally. Deforestation can lead to either an increased negative sensitivity, as drought‐tolerant forests are replaced by grasslands based on model ensemble mean, or a decreased negative sensitivity, since forests under current land cover are predicted to exhibit greater drought resistance compared to those under pre‐industrial land cover. Overall, our findings emphasize the critical role of forests in maintaining ecosystem stability and resistance to drought and temperature fluctuations, thereby implying their importance in stabilizing the carbon stock under increasingly extreme climate conditions.

Plain Language Summary Human activities, such as agricultural expansion and deforestation, have dramatically changed plant species and their distribution, affecting their growth. Given global warming and more severe and frequent drought events, it is crucial to understand whether land use and land cover changes make the terrestrial ecosystem more resilient or vulnerable to drought events and higher temperatures. We use three satellite observations as proxies for vegetation growth states and process‐based models designed for simulating vegetation growth to evaluate whether different vegetation types respond differently to drought events and temperature fluctuations. We find that forests are more resistant to drought and temperature than grasslands and croplands as observed through satellites. Models also predict decreased ecosystem sensitivity to drought when forests become grasslands, but simulate sensitivity differently when vegetation changes to croplands. Land cover changes since the pre‐industrial era have substantially altered ecosystem sensitivity to drought and temperature. Overall, our findings highlight the vital role of forests in maintaining ecosystem stability or making the ecosystem benefit from climate. Future land management strategies should consider these insights. We need to improve model performance in simulating croplands' response to drought and temperature changes to better guide future land use.

Key Points Satellite observations show that drought impacts on biomass are more severe when forests are converted to non‐forests Dynamic global vegetation models generally agree on a more negative drought sensitivity for the forest‐grassland transition Direct effects from land use and land cover changes increase negative drought impacts on deforestation hotspots, but are partially compensated by indirect effects