Extreme drought impacts have been underestimated in grasslands and shrublands globally

Abstract

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.

Experimental drought reduces the productivity and stability of a calcareous grassland

“…From our 6-year study of precipitation manipulation in a calcareous grassland, we show that simulated drought reduced productivity and its temporal stability, but that species diversity and composition were generally resistant. These results add to global findings of decreased grassland productivity with drought (Kröel-Dulay et al, 2022;Smith et al, 2024), but we add a key perspective that the reductions in productivity are coupled with reduced temporal stability, and an accentuated pattern in graminoids and legumes.…”

“…Reductions in primary productivity and biomass in response to drought have been widely reported in plant communities globally (Haddad et al, 2002;Kröel-Dulay et al, 2022;Smith et al, 2024).…”

“…weebly. com/ ) (Smith et al, 2024). The goal of the DroughtNet experimental network is to explore ecosystem sensitivity to precipitation extremes through experimental manipulations of precipitation (Knapp et al, 2017).…”

“…Productivity in grasslands is typically measured through biomass (Fahey & Knapp, 2007). Indeed, there have been wide efforts to understand how grassland biomass changes with precipitation (Grime et al, 2008;Knapp et al, 2017;Kröel-Dulay et al, 2022;Smith et al, 2024).…”

“…Generally, drought conditions reduce primary productivity in grasslands (Herben et al, 1995;Kardol et al, 2010;Smith et al, 2024;Wang et al, 2007), which can impact ecosystem services such as pollination (Phillips et al, 2018). However, despite overall reductions in productivity, grassland biomes with different baseline climatic conditions react differently, where arid or xeric biomes are more susceptible to losses in productivity with drought than mesic biomes (Cleland et al, 2013;Huxman et al, 2004;Moran et al, 2014).…”