Widespread but Divergent Drought Legacy Effects on Gross Primary Productivity Across Biomes.

Drought can impact terrestrial ecosystems concurrently but also lagged in time, that is, through legacy effects. Drought legacy effects have been identified in parameters such as tree radial growth or satellite-based greenness. Evidence in ecosystem-scale fluxes, for example, gross primary productivity (GPP), is emerging, but still limited to individual sites or specific regions. Based on GPP data at 76 long-term (≥ 7 years) eddy-covariance sites across climates and biomes, we found drought legacy effects for 26 out of 52 droughts, with magnitudes comparable to the drought concurrent effects and lasting typically up to 1 year following drought. These effects diverged in direction: 19 events led to reduced GPP in the following years (negative legacy effects), while 7 showed increased GPP (positive legacy effects). Forests experienced more negative legacy effects than non-forest ecosystems. Legacy effects were more pronounced in forests with higher hydraulic vulnerability. Our findings demonstrate the global relevance of drought legacy effects on GPP and the need for their integration into drought impact assessments.