Climate models predict more frequent, extreme, and spatially extensive droughts in the future, and drought impacts to terrestrial ecosystems have increased globally over the last century. Given the potential for intensified droughts to damage ecosystems and degrade the land carbon sink, there is a pressing scientific and societal imperative to better understand their impacts on terrestrial ecosystems. To prepare for such events, we need to understand how different ecosystems will respond to drought and the mechanisms that drive drought responses across ecosystems.
Our research explores whether global terrestrial ecosystems vary in their response to one year of extreme drought (1 in 100 year event). Specifically, we assess how one year of extreme drought affects aboveground net primary productivity (ANPP) and drought sensitivity—measured as the difference in ANPP between drought and control plots divided by the difference in precipitation received by drought and control plots. Based on the Huxman-Smith model, we expected ecosystems with higher mean annual precipitation (MAP) to be less sensitive to one year of extreme drought than ecosystems with lower MAP. To test this hypothesis, we synthesized a global dataset from the Drought-Net Research Coordination Network’s International Drought Experiment (IDE), which consists of 112 sites from 24 countries and 6 continents.
Results/Conclusions
On average, terrestrial ecosystems exhibited a negative ANPP response to one year of extreme drought, with grassland ecosystems exhibiting more negative responses in ANPP than forest ecosystems. Drought sensitivity also decreased and was less variable with increasing mean annual precipitation. Thus, our study found that terrestrial ecosystems vary substantially in their response to extreme 1-year drought. In addition, our results provide support for the Huxman-Smith model by demonstrating that water-limited terrestrial ecosystems display greater sensitivity to extreme, short-term drought than those that are less water-limited. These findings have important implications as arid ecosystems, which are important drivers of variability in the global carbon cycle, are expected to be more vulnerable to intensified drought than more mesic ecosystems.