The persistence and fall rate of snags (standing dead trees) generated during bark beetle outbreaks have consequences for the behavior, effects, and suppression of potential wildfires, hazard tree and timber salvage operations, wildlife habitat, and numerous ecosystem processes. However, post-beetle snagfall dynamics are poorly understood in most forest types. We tagged standing live and dead lodgepole pine (Pinus contorta), subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii), including beetle-killed pine snags following the peak of a recent mountain pine bark beetle outbreak in watersheds at the Fraser Experimental Forest in northcentral Colorado and sampled snagfall 10 and 12 years later. Bark beetle attacks began in 2003, peaked by 2006, and killed 78% of overstory lodgepole pine in 133 plots distributed across a range of stand and site conditions. Of those snags, only 17% fell between 2007 and 2018. Most snags broke at ground level, due to butt rot, and were oriented downhill. In contrast, snags that tipped up or snapped off above the ground were oriented with the prevailing winds. Equal numbers of snags fell singly and in multiple-tree groups, and equal numbers remained elevated rather than in contact with the ground. Lodgepole pine snagfall was 1.6-times higher on steep slopes (>40%) where dead pine density was higher, compared to flatter sites. Based on our findings and previous research, we estimate that one-half the beetle-killed lodgepole pine in high-elevation forests such as those at Fraser may fall within 15-20 yr of beetle infestation, but that some pine snags are likely to persist for decades longer. Post-outbreak snagfall dynamics create a multiple-decade legacy of bark beetle outbreaks that will persist longer in high-elevation compared to lower-elevation forests.

中文翻译：

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在美国科罗拉多州高海拔森林严重树皮甲虫侵染后的第一个十年，陷入困境。

树皮甲虫爆发期间产生的障碍物（站立的死树）的持久性和下降率会对潜在野火、危险树木和木材打捞作业、野生动物栖息地和众多生态系统过程的行为、影响和抑制产生影响。然而，在大多数森林类型中，人们对甲虫后坠落动力学知之甚少。我们标记了站立的活和死的松树 (Pinus contorta)、亚高山冷杉 (Abies lasiocarpa) 和英格曼云杉 (Picea engelmannii)，包括最近在弗雷泽 (Fraser) 流域爆发的山松树皮甲虫爆发高峰后被甲虫杀死的松树刺科罗拉多州中北部的实验森林，并在 10 年和 12 年后采样了障碍物。树皮甲虫攻击始于 2003 年，到 2006 年达到顶峰，并在分布在一系列林分和场地条件的 133 个地块中杀死了 78% 的上层山松。在这些障碍中，只有 17% 在 2007 年至 2018 年间下降。由于对接腐烂，大多数障碍在地面断裂，并且朝向下坡。相比之下，在地面上方倾斜或折断的障碍物则以盛行风为导向。相同数量的障碍物单独落下和多树组落，相同数量的障碍物保持在高处而不是与地面接触。与较平坦的地点相比，在死松密度较高的陡坡 (>40%) 上，Lodgepole 松树的绊倒率高出 1.6 倍。根据我们的发现和之前的研究，我们估计，在弗雷泽等高海拔森林中，有一半被甲虫杀死的松树可能会在甲虫侵扰的 15 到 20 年内发生，但一些松树的障碍可能会持续数十年。与低海拔森林相比，爆发后的障碍动态造成了数十年的树皮甲虫爆发遗产，这些爆发在高海拔地区将持续更长时间。