Tree mortality during drought

Understanding the drivers and mechanisms of tree mortality during drought has significant implications for forest management, especially under the background of global climate change with increasing drought frequency and severity. Tree structures have been identified as an important factor influencing tree mortality during drought, but how it functions remained controversial.Here, we provide the datasets and codes used to examined the influence of canopy structure on tree mortality in the southern Sierra Nevada during the 2012-2016 California drought. These datasets include maps of nearly 1.5 million individual trees, with their species information, tree health conditions during the drought, tree structure features, and environmental attributes. With these, we found that drought-induced tree mortality rate has a “negative-positive-negative” piecewise relationship with tree height, but remains a consistent negative relationship with neighborhood canopy structure. Our analyses further revealed that trees in a structurally complex forest and overshadowed by tall neighboring trees experienced lower mortality rate, likely due to reduced exposure to solar radiation and less water demand from evapotranspiration. Our finding suggests establishing complexity in canopy structure could improve forest resistance to drought.

解析干旱过程中树木死亡的驱动因子与作用机制，对森林经营管理具有重要意义，尤其在全球气候变化背景下，干旱发生频率与严重程度均呈上升趋势。树木结构已被证实是影响干旱期树木死亡的重要因素，但其具体作用机制仍存在争议。本研究提供了用于分析2012-2016年加州（California）干旱期间内华达山脉（Sierra Nevada）南部冠层结构对树木死亡影响的数据集与代码。该数据集涵盖近150万株单木的相关信息，包括树种信息、干旱期树木健康状况、树木结构特征以及环境属性的空间分布图。基于上述数据，研究发现干旱诱导的树木死亡率与树高呈"negative-positive-negative"分段式相关关系，而与邻体冠层结构始终呈负相关关系。进一步分析表明，生长在结构复杂森林中、且被高大邻体树木遮阴的个体，其死亡率更低，这可能得益于太阳辐射暴露量的减少以及蒸散作用（evapotranspiration）带来的水分需求降低。本研究结果表明，构建冠层结构复杂性可提升森林的干旱抗性。