Recent increases in drought frequency cause observed multi-year drought legacies in the tree rings of semi-arid forests
Recent increases in drought frequency cause observed multi-year drought legacies in the tree rings of semi-arid forests
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DOI：
10.1007/s00442-019-04550-6
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发表时间：
2019-11
期刊：
影响因子：
2.7
通讯作者：
P. Szejner;S. Belmecheri;J. Ehleringer;R. Monson
中科院分区：
文献类型：
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作者：
P. Szejner;S. Belmecheri;J. Ehleringer;R. Monson
最近对森林干旱恢复期长短的分析表明，森林干旱会造成多年的影响，特别是在半干旱的针叶林生态系统中。这种遗产通常归因于生理生态记忆，尽管干旱频率本身及其对重叠恢复时间的影响也可能有所贡献。在这里，我们描述了一个多年代的干旱遗产的研究，使用树轮碳同位素比（δ 13 C）和环宽指数（RWI）inPinus ponderosaat 13个山地网站穿越冬夏季降水梯度在美国西南部的网站和树木的选择，以避免收集偏见，存在于存档的树轮数据库。δ 13 C与大气水汽压亏缺（VPD）的季节和年际相关性很好地预测了水文气候的空间梯度和冬夏季节格局。使用VPD，我们发现在过去的二十年中，该地区极端干旱的可能性增加了70%。当不考虑最近干旱频率的增加时，在大多数站点观察到δ 13 C和RWI的多年遗产。当从树轮年表中消除干旱频率增加的趋势时，一些地点的δ 13 C和RWI都表现出较短的遗产（1-2年），而RWI则表现出较长的遗产趋势。然而，当广泛考虑整个区域和几十年时，没有观察到重大的遗产，这与过去的研究形成鲜明对比。我们的研究结果表明，观察到的多年遗产的贡献是有关的气候系统本身的变化，一个外源性因素，必须考虑沿着生理记忆。
Recent analyses on the length of drought recovery in forests have shown multi-year legacies, particularly in semi-arid, coniferous ecosystems. Such legacies are usually attributed to ecophysiological memory, although drought frequency itself, and its effect on overlapping recovery times, could also contribute. Here, we describe a multi-decadal study of drought legacies using tree-ring carbon-isotope ratios (δ13C) and ring-width index (RWI) inPinus ponderosaat 13 montane sites traversing a winter–summer precipitation gradient in the Southwestern U.S. Sites and trees were selected to avoid collection biases that exist in archived tree-ring databanks. The spatial hydroclimate gradient and winter–summer seasonal patterns were well predicted by seasonal and inter-annual correlations between δ13C and atmospheric vapor pressure deficit (VPD). Using VPD, we found that the probability of extreme drought has increased up to 70% in this region during the past two decades. When the recent increase in drought frequency was not considered, multi-year legacies in both δ13C and RWI were observed at most sites. When the increase in drought frequency was detrended from tree-ring chronologies, some sites exhibited short legacies (1–2 years) in both δ13C and RWI, and there was a sight trend for longer legacies in RWI. However, when considered broadly across the region and multiple decades, no significant legacies were observed, which contrasts with past studies. Our results reveal that a contribution to observed multi-year legacies is related to shifts in the climate system itself, an exogenous factor, that must be considered along with physiological memory.