When does extreme drought elicit extreme ecological responses?

Authors: ZHANG, FANGYUE - Chinese Academy Of Sciences; QUAN, QUAN - Chinese Academy Of Sciences; MA, FANGFANG - Chinese Academy Of Sciences; TIAN, DASHUAN - Institute Of Geographic Sciences And Natural Resources; Hoover, David; ZHOU, QINGPING - Southwest University For Nationalities; NIU, ZHULI - Chinese Academy Of Sciences

Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2019
Publication Date: 7/8/2019
Citation: Zhang, F., Quan, Q., Ma, F., Tian, D., Hoover, D.L., Zhou, Q., Niu, Z. 2019. When does extreme drought elicit extreme ecological responses? Journal of Ecology. 107(6):2553-2563. https://doi.org/10.1111/1365-2745.13226.
DOI: https://doi.org/10.1111/1365-2745.13226

Interpretive Summary: Extreme events such as changes in precipitation extremes are expected to increase with climate change. Due to the rarity of these events, there is a great deal of uncertainty how extreme an event has to be to elicit an extreme ecological response. To address this, we examined three data sets including: long-term historical records, a meta-analysis on drought experiments, and a precipitation experiment. There were three main results. First, in the historical records we found that co-occuring precipitation and ecological extremes were rare. Second, across hundreds of rainfall manipulation experiments, there were no clear thresholds between extreme precipitation and ecological responses. Finally, using a precipitation gradient experiment, we found that while multiple treatments were statistically extreme droughts, only the most extreme treatment resulted in an extreme ecological responses. There results suggest that not all climatically extreme events result in extreme ecological responses.

Technical Abstract: Global climate change models predict an increase in the frequency and intensity of precipitation extremes, with uncertain ecological impacts across ecosystems. In particular, it’s not clear when an extreme in precipitation will elicit an extreme ecological responses. In this study, we combined three approaches to explore the relationships between extreme precipitation and ecosystem responses, including a global data mining, a global meta-analysis and a site-level precipitation extremity gradient experiment. First, we examined global historical observations (1980-2013) to identify years with co-occurring extremes in precipitation amount and gross primary productivity (GPP). We found that only 15.1% and 13.7% of extreme low and high annual precipitation co-occurred with the extreme low and high GPP, respectively. Second, using a global meta-analysis approach, we analyzed data from 368 increased precipitation and 221 decreased precipitation experiments. These results suggest that ecosystem net primary productivity generally responded linearly to the precipitation treatments, and there was no significant difference in the response ratios between the extreme vs. non-extreme treatments for either increasing or decreasing precipitation. Third, we conducted a precipitation extremity gradient experiment with six precipitation levels (1/12 P, 1/4 P, 1/2 P, 3/4 P, P, 5/4 P, where P is growing season precipitation) in an alpine meadow. The results revealed that although the four treatments were statistically extreme, only 1/12 P treatment significantly reduced ANPP during the three years. Meanwhile, the species richness, diversity index and species asynchrony were significantly reduced only under 1/12 P treatment, which led to the loss of ecosystem stability and a significant reduction in productivity. In summary, we found across long-term observations and experiments that precipitation extremes, do not necessarily cause extreme responses of ecosystem productivity; it does so only if it decreases species asynchrony and causes species loss or reordering which decreases ecosystem stability. Our results highlight the key role of species asynchrony and biodiversity in determining the stability of ecosystem productivity under extreme drought event.