On underestimation of global vulnerability to tree mortality and forest die-off from hotter drought in the Anthropocene
On underestimation of global vulnerability to tree mortality and forest die-off from hotter drought in the Anthropocene
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DOI：
10.1890/es15-00203.1
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发表时间：
2015-08-01
期刊：
影响因子：
2.7
通讯作者：
McDowell, Nate G.
中科院分区：
文献类型：
--
作者：
Allen, Craig D.;Breshears, David D.;McDowell, Nate G.
模式，机制，预测，树木死亡率和相关的大规模森林死亡的后果，由于干旱伴随着温暖的温度-“更热的干旱”，人类世的一个新兴特征-是迅速扩大的文献的重点。尽管最近的观察，实验和建模研究表明，树木对干旱和相关的害虫和病原体的脆弱性增加，但研究，管理和决策社区之间关于未来树木死亡风险的争论仍然存在。我们总结了关键的死亡率相关的调查结果，区分那些暗示较低或较高水平的脆弱性。表明脆弱性较低的证据包括：[CO2]升高和水利用效率提高的森林效益;观测到的和模拟的森林生长和树冠绿化的增加;木本植物生物量、密度和范围的广泛增加;补偿性生理、形态和遗传机制;抑制生态反馈;以及森林管理的潜在缓解。相比之下，最近的研究文件更快的死亡率在炎热的干旱下，由于负面的树木生理反应和加速生物攻击。其他证据表明，更大的脆弱性，包括上升的背景死亡率;预计增加干旱频率，强度和持续时间;植被模型的局限性，如不充分代表死亡过程;从死亡的变暖反馈;和野火的协同作用。根据这些发现，我们确定了十个形成脆弱性辩论但尚未集体讨论的对比观点。我们还提出了一组全球脆弱性驱动因素，这些驱动因素具有很高的可信度：（1）干旱最终会在任何地方发生;（2）变暖会导致更热的干旱;（3）干旱期间大气水分需求随温度呈非线性增加;（4）死亡率在更热的干旱中会更快地发生，与基本生理学一致;（5）较短的干旱比较长的干旱发生得更频繁，在变暖的情况下可能成为致命的干旱，非线性地增加了致命干旱的频率;（6）死亡率相对于森林恢复所需的生长间隔迅速发生。这些高可信度驱动因素与支持更大脆弱性观点的研究相结合，支持全球森林更大脆弱性的总体观点。我们推测，死亡率脆弱性被低估的部分原因是难以预测极端气候事件的阈值反应。鉴于低估全球对干旱的脆弱性所带来的深远的生态和社会影响，我们强调研究、管理和决策社区面临的紧迫挑战。
Patterns, mechanisms, projections, and consequences of tree mortality and associated broadscale forest die-off due to drought accompanied by warmer temperatures-"hotter drought'', an emerging characteristic of the Anthropocene-are the focus of rapidly expanding literature. Despite recent observational, experimental, and modeling studies suggesting increased vulnerability of trees to hotter drought and associated pests and pathogens, substantial debate remains among research, management and policy-making communities regarding future tree mortality risks. We summarize key mortality-relevant findings, differentiating between those implying lesser versus greater levels of vulnerability. Evidence suggesting lesser vulnerability includes forest benefits of elevated [CO2] and increased water-use efficiency; observed and modeled increases in forest growth and canopy greening; widespread increases in woody-plant biomass, density, and extent; compensatory physiological, morphological, and genetic mechanisms; dampening ecological feedbacks; and potential mitigation by forest management. In contrast, recent studies document more rapid mortality under hotter drought due to negative tree physiological responses and accelerated biotic attacks. Additional evidence suggesting greater vulnerability includes rising background mortality rates; projected increases in drought frequency, intensity, and duration; limitations of vegetation models such as inadequately represented mortality processes; warming feedbacks from die-off; and wildfire synergies. Grouping these findings we identify ten contrasting perspectives that shape the vulnerability debate but have not been discussed collectively. We also present a set of global vulnerability drivers that are known with high confidence: (1) droughts eventually occur everywhere; (2) warming produces hotter droughts; (3) atmospheric moisture demand increases nonlinearly with temperature during drought; (4) mortality can occur faster in hotter drought, consistent with fundamental physiology; (5) shorter droughts occur more frequently than longer droughts and can become lethal under warming, increasing the frequency of lethal drought nonlinearly; and (6) mortality happens rapidly relative to growth intervals needed for forest recovery. These high-confidence drivers, in concert with research supporting greater vulnerability perspectives, support an overall viewpoint of greater forest vulnerability globally. We surmise that mortality vulnerability is being discounted in part due to difficulties in predicting threshold responses to extreme climate events. Given the profound ecological and societal implications of underestimating global vulnerability to hotter drought, we highlight urgent challenges for research, management, and policy-making communities.