Aim: Rainfall manipulation experiments are essential tools for deciphering mechanisms leading to variation in ecosystem stability across sites. Here, we gathered articles reporting results of experimental droughts on grasslands above-ground biomass: to identify which indices have been used to assess stability, to evaluate the overall grassland responses to drought, and to quantify the relative importance of drought characteristics and climatic conditions on explaining variation in stability.

Location: Global

Time period: 1989-2018

Major taxa studied: Grasslands

Methods: We used meta-analysis approaches to evaluate overall grassland stability in terms of resistance, recovery and resilience, and multi-model inference to assess the relative importance of different moderators on explaining variability on those three stability properties.

Results: Numerous indices of stability have been used, but they are inadequate for comparisons across sites. After applying standardized indices, we found that grasslands were resilient (biomass remained unchanged one year after drought) and exhibited a trade-off between low resistance (biomass was lost during drought) and high recovery (new biomass was produced after drought). Overall, climatic conditions and drought characteristics (intensity, duration and frequency) were not important to explain the differences in stability observed across grasslands.

Main Conclusions: Grasslands are resilient, but if drought events last longer than a year, there might be long-term declines of biomass production due to incomplete recovery. Despite the hundreds of experiments conducted in grasslands across the globe, results are still inconclusive due to four important shortcomings: 50% of the studies have failed on creating drought, 81% have not included recovery and resilience only assessing resistance, 87% have not applied quantitative indices to assess stability, and less than 1% of the studies were conducted on tropical grasslands. We discuss how to overcome those limitations to further improve our ability to ensure a stable grassland productivity under climate changes.