Extreme drought impacts have been underestimated in grasslands and shrublands globally

Authors: SMITH, MELINDA - Colorado State University; WILKINS, KATE - Colorado State University; HOLDREGE, MARTIN - Utah State University; WILFAHRT, PETER - University Of Minnesota; COLLINS, SCOTT - University Of New Mexico; KNAPP, ALAN - Colorado State University; SALA, OSVALDO - Arizona State University; DUKES, JEFFREY - Purdue University; PHILLIPS, RICHARD - Indiana University; YAHDJIAN, LAURA - University Of Buenos Aires; GHERARDI, LAUREANO - University Of California Berkeley; OHLERT, TIMOTHY - Colorado State University; BEIER, CLAUS - University Of Copenhagen; FRASER, LAUCHLAN - Thompson Rivers University; JENTSCH, ANKE - University Of Bayreuth; LOIK, MICHAEL - University Of California Santa Cruz; MAESTRE, FERNANDO - Universidad De Alicante; POWER, SALLY - Western Sydney University; YU, QIANG - Beijing Forestry University; FELTON, ANDREW - Montana State University; Larson, Julie Elizab; O'Connor, Rory

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2023
Publication Date: 1/8/2024
Citation: Smith, M.D., Wilkins, K.D., Holdrege, M.C., Wilfahrt, P., Collins, S.L., Knapp, A.K., Sala, O.E., Dukes, J.S., Phillips, R.P., Yahdjian, L., Gherardi, L.A., Ohlert, T., Beier, C., Fraser, L.H., Jentsch, A., Loik, M.E., Maestre, F.T., Power, S.A., Yu, Q., Felton, A.J., Larson, J.J., O'Connor, R.C., Zuo, X., et al. 2024. Extreme drought impacts have been underestimated in grasslands and shrublands globally. Proceedings of the National Academy of Sciences (PNAS). 121(4). Article e2309881120. https://doi.org/10.1073/pnas.2309881120.
DOI: https://doi.org/10.1073/pnas.2309881120

Interpretive Summary: Extreme droughts used to be rare but are becoming more frequent around the world because of climate change. Droughts change how ecosystems function and how much aboveground net primary productivity (ANPP) is present. Using an international drought experiment network (Drought Net) we looked at how experimental drought influences ANPP. At 55 distributed international grassland and shrubland sites there was a 21% reduction in ANPP from a nominal drought severity. In an additional 45 distributed international grassland and shrubland sites, there was a 1-in-100-year drought severity that reduced ANPP by 34%. These reductions in ANPP from a single drought event exceeds previously reported losses of ANPP in grasslands and shrublands demonstrating that current estimations of ANPP reductions from droughts are being underestimated.

Technical 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.