Legacy effects of a regional drought on aboveground net primary production in six central US grasslands
Global climate models predict increases in the frequency and severity of drought worldwide, directly affecting most ecosystem types. Consequently, drought legacy effects (drought-induced alterations in ecosystem function postdrought) are expected to become more common in ecosystems varying from deserts to grasslands to forests. Drought legacies in grasslands are usually negative and reduce ecosystem function, particularly after extended drought. Moreover, ecosystems that respond strongly to drought (high sensitivity) might be expected to exhibit the largest legacy effects the next year, but this relationship has not been established. We quantified legacy effects of a severe regional drought in 2012 on postdrought (2013) aboveground net primary productivity (ANPP) in six central US grasslands. We predicted that (1) the magnitude of drought legacy effects measured in 2013 would be positively related to the sensitivity of ANPP to the 2012 drought, and (2) drought legacy effects would be negative (reducing 2013 ANPP relative to that expected given normal precipitation amounts). The magnitude of legacy effects measured in 2013 was strongly related (r2 = 0.88) to the sensitivity of ANPP to the 2012 drought across these six grasslands. However, contrary to expectations, positive legacy effects (greater than expected ANPP) were more commonly observed than negative legacy effects. Thus, while the sensitivity of ANPP to drought may be a useful predictor of the magnitude of legacy effects, short-term (1-year) severe droughts may cause legacy effects that are more variable than those observed after multiyear droughts.
KeywordsClimate extremes Grasslands Drought legacy Drought sensitivity ANPP
We would like to thank the scientists and technicians at the Konza Prairie, Shortgrass Steppe, and the Sevilleta LTER sites for collecting, managing, and sharing data, and the scientists associated with the Prairie Heating and Carbon Dioxide Enrichment (PHACE) project in Cheyenne, WY. PHACE was supported by the US Department of Agriculture-Agricultural Research Service Climate Change, Soils and Emissions Program, and the US National Science Foundation (NSF; DEB no. 1021559). Primary support for this analysis came from the NSF Macrosystems Biology Program with additional research support from grants from the NSF to Colorado State University, Kansas State University, and the University of New Mexico for long-term ecological research. We also thank Madeline Shields, Joshua O’Malley, and all the undergraduate technicians in the Knapp and Smith labs at Colorado State University for the many hours devoted to processing samples for this study.
AKK, MDS, and SLC conceived the experiment, while AKK and RJGN designed and conducted the analysis. EMD, MJ, CJWC, SLC, and MDS contributed to data acquisition. RJGN and AKK wrote the manuscript, and all authors edited, read, and approved the final manuscript.
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