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Climate change is increasing the frequency and severity of short-term (~1 y) drought events-the most common duration of drought-globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function-aboveground net primary production (ANPP)-was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought.

Climate change is increasing the frequency and severity of short-term (~1 y) drought events—the most common duration of drought—globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function—aboveground net primary production (ANPP)—was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought.

Sustainable provision of critical ecosystem services in drylands is reliant on their stability under anthropogenic disturbances. Livestock grazing and shrub encroachment are the primary drivers of disturbance that impact their biodiversity and production dynamics. However, the effects of grazing on the stability at multiple scales, particularly following the transition from grass-dominated to shrub-encroached drylands, is still largely unexplored. Here, we conducted comparable sheep-grazing experiments in two types of drylands (grass-dominated vs. shrub-encroached grasslands) on the Mongolia Plateau to explore the effects of grazing and shrub encroachment on biodiversity and stability at multiple scales. We examined how grazing affected the temporal stability of aboveground biomass in herbaceous communities in both grass-dominated and shrub-encroached grasslands, through two potential mechanisms: insurance effects and changes in the population-level stability of individual species. We found that an increase in sheep grazing intensity had significant and negative effects on insurance effects by decreasing both species asynchrony and spatial asynchrony but it had no effects on population stability, consequently leading to reductions in herbaceous community stability of the grasslands. However, grazing-increased insurance effects canceled out grazing-decreased population stability, contributing to no changes in the community stability of shrub-encroached grasslands. Likely, because grazing-induced reductions in the relative abundance of the dominant species were more noticeable in shrub-encroached grasslands than that of in grasslands. Moreover, the grazing-decreased abundance of dominant species was directly correlated to increases in insurance effects in shrub-encroached grasslands but not in grasslands, despite the positive relationships between population stability and the relative abundance of the dominant species in both grass-dominated and shrub-encroached dryla, Sustainable provision of critical ecosystem services in drylands is reliant on their stability under anthropogenic disturbances. Livestock grazing and shrub encroachment are the primary drivers of disturbance that impact their biodiversity and production dynamics. However, the effects of grazing on the stability at multiple scales, particularly following the transition from grass-dominated to shrub-encroached drylands, is still largely unexplored. Here, we conducted comparable sheep-grazing experiments in two types of drylands (grass-dominated vs. shrub-encroached grasslands) on the Mongolia Plateau to explore the effects of grazing and shrub encroachment on biodiversity and stability at multiple scales. We examined how grazing affected the temporal stability of aboveground biomass in herbaceous communities in both grass-dominated and shrub-encroached grasslands, through two potential mechanisms: insurance effects and changes in the population-level stability of individual species. We found that an increase in sheep grazing intensity had significant and negative effects on insurance effects by decreasing both species asynchrony and spatial asynchrony but it had no effects on population stability, consequently leading to reductions in herbaceous community stability of the grasslands. However, grazing-increased insurance effects canceled out grazing-decreased population stability, contributing to no changes in the community stability of shrub-encroached grasslands. Likely, because grazing-induced reductions in the relative abundance of the dominant species were more noticeable in shrub-encroached grasslands than that of in grasslands. Moreover, the grazing-decreased abundance of dominant species was directly correlated to increases in insurance effects in shrub-encroached grasslands but not in grasslands, despite the positive relationships between population stability and the relative abundance of the dominant species in both grass-dominated and shrub-encroached dryla

Sustainable provision of critical ecosystem services in drylands is reliant on their stability under anthropogenic disturbances. Livestock grazing and shrub encroachment are the primary drivers of disturbance that impact their biodiversity and production dynamics. However, the effects of grazing on the stability at multiple scales, particularly following the transition from grass-dominated to shrub-encroached drylands, is still largely unexplored. Here, we conducted comparable sheep-grazing experiments in two types of drylands (grass-dominated vs. shrub-encroached grasslands) on the Mongolia Plateau to explore the effects of grazing and shrub encroachment on biodiversity and stability at multiple scales. We examined how grazing affected the temporal stability of aboveground biomass in herbaceous communities in both grass-dominated and shrub-encroached grasslands, through two potential mechanisms: insurance effects and changes in the population-level stability of individual species. We found that an increase in sheep grazing intensity had significant and negative effects on insurance effects by decreasing both species asynchrony and spatial asynchrony but it had no effects on population stability, consequently leading to reductions in herbaceous community stability of the grasslands. However, grazing-increased insurance effects cancelled out grazing-decreased population stability, contributing to no changes in the community stability of shrub-encroached grasslands. Likely, because grazing-induced reductions in the relative abundance of the dominant species were more noticeable in shrub-encroached grasslands than that of in grasslands. Moreover, the grazing-decreased abundance of dominant species was directly correlated to increases in insurance effects in shrub-encroached grasslands but not in grasslands, despite the positive relationships between population stability and the relative abundance of the dominant species in both grass-dominated and shrub-encroached dryl