State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing, China.
Key Laboratory of Environmental Change and Natural Disaster of Ministry of Education, Academy of Disaster Reduction and Emergency Management, Beijing Normal University, Beijing, China.
Glob Chang Biol. 2018 Nov;24(11):5380-5390. doi: 10.1111/gcb.14367. Epub 2018 Jul 29.
Droughts, which are characterized by multiple dimensions including frequency, duration, severity, and onset timing, can impact tree stem radial growth profoundly. Different dimensions of drought influence tree stem radial growth independently or jointly, which makes the development of accurate predictions a formidable challenge. Measurement-based tree-ring data have obvious advantages for studying the drought responses of trees. Here, we explored the use of abundant tree-ring records for quantifying regional response patterns to key dimensions of drought. Specifically, we designed a series of regional-scaled "natural experiments," based on 357 tree-ring chronologies from Southwest USA and location-matched monthly water balance anomalies, to reveal how tree-ring responds to each dimension of drought. Our results showed that tree-ring was affected significantly more by the water balance condition in the current hydrological year than that in the prior hydrological year. Within the current hydrological year, increased drought frequency (number of dry months) and duration (maximum number of consecutive dry months) resulted in "cumulative effects" which amplified the impacts of drought on trees and reduced the drought resistance of trees. Drought events that occurred in the pregrowing seasons strongly affected subsequent tree stem radial growth. Both the onset timing and severity of drought increased "legacy effects" on tree stem radial growth, which reduced the drought resilience of trees. These results indicated that the drought impact on trees is a dynamic process: even when the total water deficits are the same, differences among the drought processes could lead to considerably different responses from trees. This study thus provides a conceptual framework and probabilistic patterns of tree-ring growth response to multiple dimensions of drought regimes, which in turn may have a wide range of implications for predictions, uncertainty assessment, and forest management.
干旱具有多重特征，包括频率、持续时间、严重程度和起始时间，会对树木的径向生长产生深远影响。不同维度的干旱独立或共同影响树木的径向生长，这使得准确预测的发展成为一项艰巨的挑战。基于测量的树木年轮数据在研究树木对干旱的响应方面具有明显优势。在这里，我们探讨了利用丰富的树木年轮记录来量化区域对干旱关键维度的响应模式。具体来说，我们设计了一系列基于美国西南部 357 个树木年轮年表和位置匹配的月度水量平衡异常的区域尺度“自然实验”，以揭示树木年轮对每个干旱维度的响应。我们的研究结果表明，树木年轮受到当前水文年的水量平衡状况的影响明显大于前一年的影响。在当前水文年内，干旱频率（干旱月数）和持续时间（连续干旱月数的最大值）的增加会产生“累积效应”，放大干旱对树木的影响，并降低树木的抗旱能力。发生在生长前期的干旱事件强烈影响后续的树木径向生长。干旱的起始时间和严重程度增加了对树木径向生长的“滞后效应”，降低了树木的抗旱能力。这些结果表明，干旱对树木的影响是一个动态过程：即使总水分亏缺相同，干旱过程的差异也可能导致树木产生明显不同的响应。因此，本研究为树木对多个干旱制度维度的生长响应提供了一个概念框架和概率模式，这反过来可能对预测、不确定性评估和森林管理产生广泛的影响。
