Dead Again: Predictions of repeat tree die-off under hotter droughts confirm mortality thresholds for a dryland conifer species

Tree die-off, driven by extreme drought and exacerbated by a warming climate, is occurring rapidly across every wooded continent - threatening carbon sinks and other ecosystem services provided by forests and woodlands. Forecasting the spatial patterns of tree die-off in response to drought is a priority for the management and conservation of forested ecosystems under projected future hotter and drier climates. Several drought-related metrics have recently been proposed to predict the mortality threshold (i.e., tipping point) for Pinus edulis, a model tree species in many studies of drought-induced tree die-off. To improve future capacity to forecast tree mortality, we used a severe drought in 2018 across the southwestern United States as a natural experiment. We compared the ability of published mortality thresholds derived from four drought metrics (the Forest Drought Severity Index, the Standardized Precipitation Evapotranspiration Index, and raw values of precipitation and vapor pre...由极端干旱驱动、且因气候变暖而加剧的树木死亡事件，正快速波及所有覆盖森林植被的大陆，严重威胁森林与林地所提供的碳汇及其他生态系统服务。在未来预估的暖干化气候背景下，预测干旱诱导的树木死亡空间格局，是森林生态系统管理与保护的核心优先事项。近期已有多项干旱相关指标被提出，用于预测埃氏松（Pinus edulis）的死亡阈值（即临界点）——该物种是诸多干旱诱导树木死亡研究中的模式树种。为提升未来树木死亡事件的预测能力，我们以2018年美国西南部发生的严重干旱作为自然实验，对比了基于四项干旱指标所得到的已发表死亡阈值的预测性能，这四项指标分别为：森林干旱严重度指数（Forest Drought Severity Index）、标准化降水蒸散指数（Standardized Precipitation Evapotranspiration Index），以及降水与水汽压的原始值……