Legacy effects of a regional drought on aboveground net primary production in six central US grasslands

Authors: GRIFFIN-NOLAN, ROBERT - Colorado State University; CARROLL, CHARLES - Colorado State University; Denton, Elsie; Johnston, Melissa; COLLINS, SCOTT - University Of New Mexico; SMITH, MELINDA - Colorado State University; KNAPP, ALAN - Colorado State University

Submitted to: Plant Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2018
Publication Date: 5/5/2018
Citation: Griffin-Nolan, R.J., Carroll, C.J., Denton, E.M., Johnston, M.K., Collins, S.L., Smith, M.D., Knapp, A.K. 2018. Legacy effects of a regional drought on aboveground net primary production in six central US grasslands. Plant Ecology. 219(5):505-515. https://doi.org/10.1007/s11258-018-0813-7.
DOI: https://doi.org/10.1007/s11258-018-0813-7

Interpretive Summary: Legacy effects are changes to an ecosystem that persist after a climatic event has taken place. As severe weather events, such as extreme drought, increase in frequency with climate change, knowing how long ecosystem changes persist after the event will aid in management. Preliminary research expects drought legacies in grassland ecosystems to be primarily negative and reduce ecosystem function. Additionally, it might be expected that ecosystems that are more sensitive to drought in the moment would exhibit greater negative legacies. This has not been tested. In this study, we examined legacy effects after the extreme, central US wide drought of 2012. Our study included six sites across NM, CO, WY and KS. We found that while legacy effects were common, positive legacy effects (i.e. improved ecosystem function) occurred at more sites than negative legacy effects. Some sites displayed no legacy effects at all. Legacy effects seem highly site dependent and more must be learned about what causes them before they can become a useful predictor for management.

Technical Abstract: 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.