The global rise in temperature and associated changes in climate have led to decline of forests around the globe, across multiple species and ecosystems. Yellow‐cedar (Callitropsis nootkatensis) decline is one of the most severe in North America. We found abundant evidence of tree decline and mortality on Haida Gwaii across multiple watersheds and over a range of elevations. This decline on Haida Gwaii parallels the broader yellow‐cedar decline in terms of spatial distribution, symptoms, magnitude, and timing. However, Haida Gwaii has a more temperate climate and ephemeral snowpack than declining yellow‐cedar forests in Alaska where the link to climate was first uncovered. Given these important differences, we investigated several possible drivers both at the local and at the regional scale, using population demography, dendrochronology, and daily weather data. We explored stand dynamics as a driver and tested the known link to climate. Our results are inconsistent with stand dynamics as a driver of elevated decline and mortality. Neither increased competition nor aging of a cohort explains the decline. Alternatively, the magnitude and timing of the decline are consistent with well‐documented long‐term directional trends in regional climate. Onset of basal area increment decline and mortality have been accumulating over time, with increased rates since the 1980s. Our sites were located at the edge of the expected range of mortality, and we found only four thaw–freeze events over the past ~80 yrs. However, superposed epoch analysis using daily weather data revealed that mortality and onset of decline events were associated with warmer winter conditions, consistent with the drivers from Alaska. Rather than isolated extreme thaw–freeze events, warmer winter temperatures on Haida Gwaii may mean less cold hardening throughout the winter, which exposes yellow‐cedar’s fine roots to varying degrees of freezing damage over multiple winter thaw–freeze cycles, causing physiological stress, tree decline, and eventual death.

中文翻译：

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海达瓜伊岛群岛由气候引起的黄柏下降

全球温度上升以及相关的气候变化导致全球范围内多种物种和生态系统的森林退化。黄柏（Callitropsis nootkatensis））下降是北美最严重的下降之一。我们发现，在多个流域和一系列高程上，海达瓜的树木砍伐和死亡的大量证据。在空间分布，症状，大小和时间上，海达瓜的下降与更广泛的黄柏下降平行。但是，相比最早发现气候联系的阿拉斯加衰退的黄柏森林，海达瓜的气候和短暂的积雪更为温和。鉴于这些重要的差异，我们使用人口人口统计学，树木年代学和每日天气数据调查了本地和区域范围内的几种可能的驱动因素。我们以驱动力的形式探讨了展位动力学，并测试了与气候的已知联系。我们的结果与导致下降和死亡率升高的林分动态不一致。竞争的增加或同龄人的老化都不能解释下降的原因。另外，下降的幅度和时间与区域气候中有据可查的长期方向性趋势一致。自1980年代以来，随着时间的推移，基底面积增加的减少和死亡率的发作一直在累积。我们的站点位于预期死亡率范围的边缘，并且在过去约80年中，我们仅发现了4次解冻事件。但是，使用每日天气数据进行的历时分析表明，死亡率和下降事件的发生与冬天暖和的天气有关，与阿拉斯加的驾驶员一致。海达瓜（Haida Gwaii）较暖的冬季温度可能意味着整个冬季较少的冷硬化，而不是孤立的极端解冻事件。