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Bark beetles and wildfires: How does forest recovery change with repeated disturbances in mixed conifer forests?

机译:树皮甲虫和野火:针叶树混交林中反复受到干扰,森林恢复如何变化?

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Increased wildfire activity and recent bark beetle outbreaks in the western United States have increased the potential for interactions between disturbance types to influence forest characteristics. However, the effects of interactions between bark beetle outbreaks and subsequent wildfires on forest succession remain poorly understood. We collected data in dry mixed conifer forests across Idaho and western Montana to test whether vegetation responses differ between sites experiencing single and repeated disturbances. We compared tree seedling density and age, surface fuel loading, and stand structure characteristics in stands that experienced either high severity wildfire, large‐scale tree mortality from bark beetles, or stands that experienced high bark beetle mortality followed by severe wildfire within 3–8 years of attack. Tree seedling density was 300–400% higher in gray bark beetle‐affected stands than burned sites, but there was no evidence that a beetle and wildfire interaction affected seedling densities. The age distribution of Douglas‐fir and grand fir seedlings in stands with repeated disturbances differed from those that only experienced wildfire, suggesting that seed availability varies between these stands. Though both bark beetle outbreaks and wildfires resulted in the death of numerous large trees and surface woody fuel loads 100–200% greater than control sites, the creation of large snags and higher fuel loads across the landscape may have ecological benefits. Compounding effects of bark beetle activity and wildfires were not observed in surface fuel loadings or stand densities. Overall, the effects of high severity wildfire drove post‐disturbance fuel complexes and succession whereas the effects of Dendroctonus pseudotsugae and Dendroctonus brevicomis outbreaks before wildfires resulted in minimal post‐wildfire differences. We conclude that although seedling age structure is responsive to bark beetle and fire interactions, in terms of fuel complexes and tree densities these disturbances are non‐additive and compounding effects on forest trajectory of dry mixed conifer forests of the northern Rockies were not supported.
机译:在美国西部,野火活动增加和最近的树皮甲虫暴发增加了干扰类型之间相互作用以影响森林特征的可能性。然而,对树皮甲虫暴发与随后的野火之间的相互作用对森林演替的影响仍然知之甚少。我们收集了爱达荷州和蒙大拿州西部的干混针叶林的数据,以测试经历单一和反复干扰的地点之间的植被反应是否不同。我们比较了经历高强度野火,树皮甲虫大规模造成树木死亡或经历高树皮甲虫死亡率然后在3–8内发生严重野火的林分中的树木幼苗密度和年龄,表面燃料负荷以及林分结构特征。多年的进攻。受灰树皮甲虫侵害的林木的树苗密度比烧毁的树苗高300-400%,但没有证据表明甲虫和野火的相互作用会影响幼苗的密度。受到多次干扰的林分中的花旗松和大杉树苗的年龄分布与仅经历野火的林分不同,这表明这些林分之间的种子可利用性有所不同。尽管树皮甲虫的爆发和野火都导致大量大树的死亡和地表木质燃料负荷比控制地点大100-200%,但在整个景观中形成大障碍和增加燃料负荷可能具有生态效益。在表面燃料负荷或林分密度中未观察到树皮甲虫活性和野火的复合效应。总体而言,高强度野火的影响驱使了灾后燃料的复杂性和演替,而野火之前的 Dendroctonus pseudotsugae和 Dendroctonus brevicomis爆发的影响导致的野火后差异最小。我们得出的结论是,尽管幼苗年龄结构对树皮甲虫和火的相互作用有反应,但就燃料复合物和树木密度而言,这些扰动是非累加性的,并且不支持洛矶山脉北部干混针叶林的森林轨迹复合效应。

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