Significant drought legacy effects on gross primary productivity detected in terrestrial ecosystems across the globe

Abstract

The frequency, intensity, and duration of drought are expected to increase in many regions under climate change. A large number of studies have shown that droughts influence terrestrial ecosystems. Yet, assessments of drought impacts on ecosystem carbon cycling usually focus on instantaneous effects during drought, while legacy effects following drought can be important as well. Here, we provide the first synthesis about drought legacy effects on gross primary productivity (GPP) based on 90 long-term (>=7 years) eddy covariance sites across the globe. We predict the ‘potential’ GPP in the 2 years following drought (considered legacy years) based on a random forest model trained by data in non-legacy time periods. Legacy effects are inferred based on the difference between actual and ‘potential’ GPP in legacy periods. Results show widespread drought legacy effects on GPP across the globe. The change in GPP due to legacy effects is of the same order of magnitude as instantaneous effects. Furthermore, using the unconditional dependence test on many different potential factors, we find legacy effects unconditionally depend on aridity, instantaneous impact intensity, and species richness in forests. The conditional dependence test further reveals aridity primarily modulates legacy effects in forests.  These findings highlight the significance of drought legacy effects on ecosystem carbon cycling across the globe. We find a dominant role of climatic controls on drought legacy effects, while species diversity effects did not explain variability in drought legacy effects.