Condon Kathleen V, Carroll Charles J W, Griffin-Nolan Robert J, Slette Ingrid J, Wilkins Kate D, Smith Melinda D, Knapp Alan K
Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, USA.
Department of Forest and Rangeland Stewardship, Colorado State University, Fort Collins, CO, USA.
Oecologia. 2025 Jun 19;207(7):104. doi: 10.1007/s00442-025-05746-9.
Climate change is increasing the frequency and severity of droughts globally, and grasslands are particularly vulnerable to such hydrological extremes. Drought effects at the ecosystem scale have been assessed both experimentally and through the study of naturally occurring drought, with emerging evidence that the magnitude of drought effects may vary depending on the approach used. We took advantage of a decadal study of four grasslands to directly contrast responses of aboveground net primary productivity (ANPP) to simulated vs. natural drought. The grasslands spanned a ~ threefold mean annual precipitation gradient (335-857 mm) and were all subjected to a natural 1-year drought (~ 40% reduction in precipitation from the long-term mean) and a 4 year experimental drought (~ 50% precipitation reduction). We expected that the 4 year drought would reduce ANPP more, and that post-drought recovery would be delayed, compared to the 1-year drought. We found instead that the short-term natural drought reduced ANPP more strongly than the simulated drought in all grasslands (~ 10 to ~ 50%) likely due to the co-occurrence of higher temperatures and vapor pressure deficits with reduced precipitation. Post-drought recovery was site specific and each site differed in their recovery from the natural and experimental droughts. These results align with past analyses that experiments that only manipulate soil moisture likely underestimate the magnitude of natural drought events. However, experiments can provide valuable insight into the relative sensitivity of ecosystems to reduced precipitation and soil moisture, a key aspect of drought.
气候变化正在增加全球干旱的频率和严重程度，而草原尤其容易受到此类水文极端事件的影响。已通过实验以及对自然发生的干旱进行研究，评估了干旱在生态系统尺度上的影响，新出现的证据表明，干旱影响的程度可能因所采用的方法而异。我们利用了一项对四个草原进行的十年研究，直接对比地上净初级生产力（ANPP）对模拟干旱和自然干旱的响应。这些草原跨越了约三倍的年平均降水量梯度（335 - 857毫米），并且都经历了一次为期1年的自然干旱（降水量比长期平均值减少约40%）和一次为期4年的实验干旱（降水量减少约50%）。我们预计，与1年干旱相比，4年干旱对ANPP的降低幅度更大，且干旱后的恢复会延迟。然而，我们发现，在所有草原中，短期自然干旱对ANPP的降低作用比模拟干旱更强（约10%至约50%），这可能是由于较高温度和水汽压亏缺与降水量减少同时出现所致。干旱后的恢复具有地点特异性，每个地点从自然干旱和实验干旱中的恢复情况各不相同。这些结果与过去的分析一致，即仅操纵土壤湿度的实验可能低估了自然干旱事件的影响程度。然而，实验可以为生态系统对降水量和土壤湿度减少的相对敏感性提供有价值的见解，而这是干旱的一个关键方面。
