Figures for "California forest die-off linked to multi-year deep soil drying in 2012-2015 drought"

Data underlying main figures in "California forest die-off linked to multi-year deep soil drying in 2012-2015 drought", published in Nature-Geoscience, July 2019, ML Goulden and RC Bales. 

Abstract of paper: Widespread episodes of recent forest die-off have been tied to the occurrence of anomalously warm droughts, though the underlying mechanisms remain inadequately understood. California’s 2012-2015 drought, with exceptionally low precipitation and warmth and widespread conifer death, provides an opportunity to explore the chain of events leading to forest die-off. Here we present the spatial and temporal patterns of die-off and moisture deficit during California’s drought based on field and remote-sensing observations.  We found that die-off was closely tied to multi-year deep-rooting-zone drying, and that this relationship provides a framework to diagnose and predict mortality. Marked tree death in an intensively studied Sierra Nevada forest followed a four-year moisture overdraft, with cumulative 2012-2015 evapotranspiration exceeding precipitation by ~1500 mm and subsurface moisture exhaustion to 5-15 m depth. Observations across the entire Sierra Nevada further linked tree death to deep drying, with die-off and moisture overdraft covarying across latitude and elevation. Unusually dense vegetation and warm temperatures accelerated southern Sierran evapotranspiration in 2012-2015, intensifying overdraft and compounding die-off by an estimated 55%. Climate change is expected to further amplify evapotranspiration and moisture overdraft during drought, potentially increasing Sierran tree death during drought by ~15 to 20% per oC.

Methods
See Methods section of paper and figure captions for details.

发表于2019年7月《自然-地球科学》（Nature-Geoscience）、作者为ML Goulden与RC Bales的论文《2012-2015年干旱期加州森林枯亡与多年深层土壤干燥相关》的主图支撑数据集。

论文摘要：近期频发的森林枯亡事件与异常暖旱事件存在关联，但其背后的机制仍未得到充分阐明。2012-2015年加州干旱期降水异常偏少、气温偏高，且针叶林大面积死亡，这为探究森林枯亡的完整事件链提供了绝佳研究契机。本研究基于野外观测与遥感观测数据，揭示了加州干旱期间森林枯亡与水分亏缺的时空分布特征。
研究发现，森林枯亡与多年深层根系区土壤干燥存在紧密关联，这一关系可为树木死亡率的诊断与预测提供理论框架。在被深入研究的内华达山脉（Sierra Nevada）林区，显著的树木死亡事件发生在四年水分透支之后：2012-2015年累计蒸散发（evapotranspiration）量较降水量高出约1500毫米，且5至15米深度的地下土壤水分完全耗竭。对整个内华达山脉的观测进一步证实，树木死亡与深层土壤干燥相关，森林枯亡范围与水分透支程度随纬度和海拔梯度协同变化。2012-2015年期间，异常茂密的植被与偏高的气温加快了内华达山脉南部的蒸散发速率，加剧了水分透支，据估算使森林枯亡规模扩大了55%。气候变化预计将进一步加剧干旱期的蒸散发与水分透支，每升温1摄氏度，内华达山脉干旱期的树木死亡率可能提升约15%至20%。

研究方法
详见论文研究方法章节与图注。