Snags (standing dead trees) are important components of forest ecosystems that, among other benefits, provide critical habitat for many species of wildlife, but also represent important safety concerns to firefighters, forest workers, and the public. We identified factors that influence the fall rates of lodgepole pines, Pinus contorta Dougl. ex Loud., killed by bark beetles during a severe regional-scale outbreak of mountain pine beetle, Dendroctonus ponderosae Hopkins, that occurred in 2004–2012. Data were obtained during annual assessments (2010–2019) of a network of 107 0.081-ha circular plots installed in P. contorta forests in Colorado, Idaho, Montana, Utah and Wyoming, U.S. A total of 3789 P. contorta snags were monitored, and in each case we recorded, among other variables, the year the snag was created and the year the snag fell to the forest floor. Among snag age classes (i.e., number of years since tree death), the highest number of snags (1046) were 12 years since death (YSD), and those 13 and 14 YSD exhibited the lowest fall rates to date (<10%) despite being the oldest in our study. Snags 13 and 14 YSD were among the largest in diameter. Snag fall occurred in every snag age class from 1 to 14 YSD, with the greatest proportion of snag fall events occurring 4–8 YSD. By 2019, 24.7% (937) of snags fell to the forest floor. We modeled snag fall using a Cox’s proportional-hazards model that included six covariates of interest: elevation (m), slope aspect (categorical, cardinal direction), slope (%), canopy cover (%), snag height (m), and snag height:dbh (m, diameter at 1.37 m in height). Slope aspect had the strongest influence on fall rates. Northern aspects, increased canopy cover, and taller snag heights decreased the probability of snag fall. Conversely, southern aspects and increased height:dbh ratios (i.e., taller, skinner snags) increased the probability of snag fall. The predicted half-life (i.e., the amount of time since death required for 50% of the snag population to fall to the forest floor) was ~16 YSD after which the function predicted a linear, ~0.04/year decline in snag survival probability 15–30 YSD. The observed longevity of P. contorta snags confers important ecological benefits for some wildlife, and may offer opportunities for extended periods of salvage. However, checking (cracks) rapidly occurred, and many snags 6 YSD and older had at least one check at 1.37 m and 5.5 m in height, which can negatively impact lumber recovery. The relatively slow snag fall rates observed in our study also lengthen concerns regarding hazard trees, human safety, and protection of critical infrastructure. The implications of these and other results to management of P. contorta forests are discussed.

障碍物（死木）是森林生态系统的重要组成部分，除其他好处外，它们为许多野生动植物提供了重要的栖息地，同时也对消防员，林业工作者和公众构成了重要的安全隐患。我们确定了影响黑松，Pinus contorta Dougl下降率的因素。前大声，在2004-2012年间在一次区域性严重的山松甲虫Dendroctonus灰褐色的霍普金斯病暴发中被树皮甲虫杀死。数据是在P内安装的107个0.081公顷圆形样地网络的年度评估（2010-2019年）期间获得的。扭叶松森林在科罗拉多州，爱达荷州，蒙大拿州，犹他州和怀俄明州，美国共有3789的P。扭曲监控障碍物，在每种情况下，我们都记录了障碍物的创建年份和障碍物跌落到森林地面的年份等变量。在障碍物年龄类别（即，树木死亡以来的年数）中，障碍物的最高数量（1046）是死亡以来的12年（YSD），而迄今为止，这13和14个YSD的跌倒率最低（<10％）尽管是我们研究中最古老的。截齿13和14 YSD的直径最大。从1到14 YSD的每个障碍年龄段都发生障碍坠落，最大的障碍坠落事件发生在4-8 YSD。到2019年，有24.7％（937）的障碍物掉到了森林地面上。我们使用Cox比例风险模型对障碍物下降进行了建模，其中包括六个相关协变量：海拔高度（m），坡度（类别，基本方向），坡度（％），树冠覆盖率（％），障碍物高度（m），障碍高度：dbh（米，直径为1.37 m）。坡度对下降率的影响最大。北方方面，树冠覆盖增加，并且更高的障碍物高度降低了障碍物掉落的可能性。相反，南部地区和身高与身高比值的增加（例如，较高的，更苗条的障碍物）增加了障碍物掉落的可能性。预测的半衰期（即自50％的障碍物落入森林地面所需的死亡时间）为〜16 YSD，此后该函数预测了障碍物存活率呈线性〜0.04 /每年的下降15-30日元。观察到的寿命 南方方面和身高与身高比值的增加（例如，更高的，更苗条的障碍物）增加了障碍物掉落的可能性。预测的半衰期（即自50％的障碍物落入森林地面所需的死亡时间）为〜16 YSD，此后该函数预测了障碍物存活率呈线性〜0.04 /每年的下降15-30日元。观察到的寿命 南方方面和身高与身高比值的增加（例如，更高的，更苗条的障碍物）增加了障碍物掉落的可能性。预测的半衰期（即自50％的障碍物落入森林地面所需的死亡时间）为〜16 YSD，此后该函数预测了障碍物存活率呈线性〜0.04 /每年的下降15-30日元。观察到的寿命P。contorta奴隶赋予某些野生生物重要的生态效益，并可能提供长期的打捞机会。但是，检查（裂纹）迅速发生，许多YSD 6岁及以上的障碍物在高度1.37 m和5.5 m处至少有一个检查，这可能会对木材的恢复产生负面影响。在我们的研究中观察到的相对较慢的障碍下降率也延长了人们对危险树，人类安全和关键基础设施的保护的担忧。这些和其他结果对P的管理的影响。讨论了contorta森林。