Background tree mortality is a complex process that requires large sample sizes and long timescales to disentangle the suite of ecological factors that collectively contribute to tree stress, decline, and eventual mortality. Tree mortality associated with acute disturbance events, in contrast, is conspicuous and frequently studied, but there remains a lack of research regarding the role of background mortality processes in mediating the severity and delayed effects of disturbance. We conducted an empirical study by measuring the rates, causes, and spatial pattern of mortality annually among 32,989 individual trees within a large forest demography plot in the Sierra Nevada. We characterized the relationships between background mortality, compound disturbances (fire and drought), and forest spatial structure, and we integrated our findings with a synthesis of the existing literature from around the world to develop a conceptual framework describing the spatio‐temporal signatures of background and disturbance‐related tree mortality. The interactive effects of fire, drought, and background mortality processes altered the rate, spatial structuring, and ecological consequences of mortality. Before fire, spatially non‐random mortality was only evident among small (1 < cm DBH ≤ 10)‐ and medium (10 < cm DBH ≤ 60)‐diameter classes; mortality rates were low (1.7% per yr), and mortality was density‐dependent among small‐diameter trees. Direct fire damage caused the greatest number of moralities (70% of stems ≥1 cm DBH), but the more enduring effects of this disturbance on the demography and spatial pattern of large‐diameter trees occurred during the post‐fire mortality regime. The combined effects of disturbance and biotic mortality agents provoked density‐dependent mortality among large‐diameter (≥60 cm DBH) trees, eliciting a distinct post‐disturbance mortality regime that did not resemble the pattern of either pre‐fire mortality or direct fire effects. The disproportionate ecological significance of the largest trees renders this mortality regime acutely consequential to the long‐term structure and function of forests.

中文翻译：

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野火和干旱减轻了树木死亡率的空间因素

背景树木死亡率是一个复杂的过程，需要大量的样本和较长的时间规模才能弄清共同导致树木压力，衰退和最终死亡的一系列生态因素。相比之下，与急性干扰事件相关的树木死亡率是引人注目的并且经常被研究，但是关于背景死亡率过程在介导干扰的严重性和延迟影响方面的作用仍然缺乏研究。我们通过测量内华达山脉一个大型森林人口统计图中的32,989棵单株树中每年的死亡率，原因和空间格局进行了一项实证研究。我们描述了背景死亡率，复合干扰（火灾和干旱）与森林空间结构之间的关系，我们将研究结果与来自世界各地的现有文献进行了综合，以建立一个概念框架，描述了背景和与干扰有关的树木死亡率的时空特征。火，干旱和本底死亡率过程的相互作用影响了死亡率的发生率，空间结构和生态后果。火灾前，空间非随机死亡率仅在小（1 <cm DBH≤10）直径和中等（10 <cm DBH≤60）直径等级中明显；死亡率低（每年1.7％），并且小径树的死亡率与密度有关。直接火伤造成最多的道德损失（70％的茎≥1 cm DBH），但是这种干扰对大直径树木的人口统计和空间格局的持久影响发生在火灾后的死亡时期。干扰和生物死亡因子的共同作用在大直径（≥60 cm DBH）树中引起了密度依赖性死亡率，从而引发了一种独特的扰动后死亡率机制，既不类似于火灾前死亡率或直接火灾效应。大树的生态重要性不成比例，这使这种死亡制度对森林的长期结构和功能产生了严重的后果。引发了一种独特的扰动后死亡率制度，既不类似于火灾前的死亡率，也不类似于直接火灾效应。大树的生态重要性不成比例，使这种死亡制度对森林的长期结构和功能产生了严重的后果。引发了一种独特的扰动后死亡率制度，既不类似于火灾前的死亡率，也不类似于直接火灾效应。大树的生态重要性不成比例，这使这种死亡制度对森林的长期结构和功能产生了严重的后果。