Understanding drivers of disturbances across scales is critical as environmental constraints change in a warming climate. Outbreaks of native bark beetles (Curculionidae: Scolytinae) are key natural disturbances that shape the structure and function of conifer forests across the northern hemisphere. While drivers of bark beetle outbreaks have been studied extensively at spatial scales ranging from stands to continents, within‐stand processes governing individual tree mortality in an outbreak are less well understood. Here, we use a spatially explicit long‐term monitoring dataset of a lodgepole pine (Pinus contorta var. latifolia) forest (>9000 individually mapped trees in three 2‐ha plots) impacted by a severe mountain pine beetle (Dendroctonus ponderosae) outbreak to explore interactions among fine scale drivers of beetle‐caused tree mortality. Using a Bayesian spatial modeling approach, we evaluated how tree scale and tree neighborhood scale characteristics interact with tree size to mediate host tree susceptibility to mountain pine beetle outbreak in the Southern Rocky Mountains (USA). We found evidence that both tree growth rate preceding the outbreak and neighborhood structure (within a 10 meter radius of the host tree) mediate the effect of tree size, and that the direction and magnitude of these mediating effects vary with tree size. Tree scale mortality probability increased with pre‐outbreak growth rate for small to medium sized host trees (~10–25 cm diameter), but that same effect was not detected for large trees. Conversely, tree scale mortality probability increased with greater neighborhood density, with the most pronounced effects for medium to large sized host trees (~15–30 cm diameter). Within‐stand topographic variability was not an important predictor of mortality probability; among stands, however, the stand in the driest topographic position experienced the greatest overall mortality. By explicitly considering how within‐stand heterogeneity mediates individual tree scale susceptibility to bark beetle outbreak, our findings bridge an important gap in understanding multi‐scale drivers of disturbance dynamics.

中文翻译：

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邻域环境在严重的树皮甲虫暴发中介导寄主树死亡的可能性

随着环境的变化在气候变暖的情况下，跨尺度了解扰动的驱动因素至关重要。本地树皮甲虫的暴发（Curculionidae：Scolytinae）是影响北半球针叶林结构和功能的关键自然干扰。虽然从林分到大陆的空间尺度上对树皮甲虫暴发的起因进行了广泛的研究，但对于控制暴发中单个树木死亡率的树立过程却知之甚少。在这里，我们使用了受到严重山松甲虫（Dendroctonus Pokerosae）影响的黑松（Pinus contorta var。latifolia）森林（在三个2公顷的地块中有9000棵以上单独绘制的树木）的空间明确的长期监测数据集。）暴发，以探讨甲虫引起的树木死亡率的精细尺度驱动因素之间的相互作用。使用贝叶斯空间建模方法，我们评估了树木规模和树木邻里规模特征如何与树木大小相互作用，以调解寄主树木对美国落基山脉南部松树甲虫暴发的敏感性。我们发现证据表明，暴发之前的树木生长速度和邻域结构（在宿主树的半径10米以内）均会影响树木大小的影响，并且这些中介作用的方向和大小会随树木大小而变化。对于中小型寄主树（直径约10–25 cm），树规模的死亡率随着暴发前生长速度的增加而增加，但是对于大树却没有发现相同的影响。反过来，树木密度的死亡率随着邻里密度的增加而增加，对中型至大型寄主树（直径约15–30 cm）的影响最为明显。站内地形变异性不是死亡率概率的重要预测指标；然而，在林分中，处于最干燥地形位置的林分总体死亡率最高。通过明确考虑支架内异质性如何介导单个树规模对树皮甲虫暴发的敏感性，我们的发现弥合了在理解扰动动力学的多尺度驱动因素方面的重要差距。处于最干燥地形位置的林分总体死亡率最高。通过明确考虑支架内异质性如何介导单个树规模对树皮甲虫暴发的敏感性，我们的发现弥合了在理解扰动动力学的多尺度驱动因素方面的重要差距。处于最干燥地形位置的林分总体死亡率最高。通过明确考虑种间内异质性如何介导单个树规模对树皮甲虫暴发的敏感性，我们的发现弥合了在理解扰动动力学的多尺度驱动因素方面的重要差距。