ABSTRACT Fire is a critical ecosystem process that has played a key role in shaping forests throughout the Beartooth Mountains in northwestern Wyoming. The highly variable topography of the area provides ideal conditions to compare fire regimes across contiguous forest types, yet pyro-dendrochronological research in this area is limited. We reconstructed fire frequency, tree age structure, and post-fire tree growth response in the Clarks Fork Ranger District of the Shoshone National Forest to infer variations in historical fire behavior and stand effects. We collected fire-scarred trees and plot-based tree ages on plots ranging 0.5-5 km2 in size across two forest types separated by 2 km: a lower-elevation forest of mixed Douglas-fir and lodgepole pine and a higher elevation treeline forest dominated by whitebark pine. Fires occurred in the lower-elevation forest in 1664, 1706, 1785, 1804, 1846, and 1900 with a mean fire return interval of 47 years. The fires in 1804 and 1900 were also recorded in the higher elevation forest, with significant tree mortality at high elevation in the 1900 fire. Both forests were multi-aged with little evidence of tree cohorts in response to severe, stand-replacing events. On average, tree growth increased after fires, with mean ring widths after fire 39% wider in Douglas-fir and 40% wider in lodgepole pine than pre-fire averages, suggesting that some tree mortality likely occurred in association with lower-elevation forest fires. Burns were more frequent in the lower-elevation forest and were occasionally able to spread into the upper-elevation whitebark stand. Although we suspect the transition of fires from low-to high-elevation occurred during drier years, we did not find any relationship between fire years and available climatic reconstructions via superposed epoch analysis. Regeneration during the 20th Century in the whitebark forest documents recovery of this forest after the 1900 moderate-severity fire event. Finally, especially in the lower-elevation Douglas-fir forest, the period since the last recorded fire (1900) appears to be longer than any fire-free period in the historical record, suggesting that fire exclusion may be creating changes in landscape and patch-scale stand structures, which will likely impact future fire behavior, especially the extent of crown-replacing fire, in these forests.

中文翻译：

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怀俄明州南熊牙山不同森林类型的火灾历史

摘要 火灾是一个关键的生态系统过程，它在整个怀俄明州西北部的熊牙山脉形成森林方面发挥了关键作用。该地区高度多变的地形为比较相邻森林类型的火灾状况提供了理想的条件，但该地区的火树年代学研究有限。我们重建了肖肖尼国家森林克拉克斯福克游侠区的火灾频率、树龄结构和火灾后树木生长响应，以推断历史火灾行为和林分效应的变化。我们在面积为 0.5-5 平方公里的地块上收集了火伤树木和基于地块的树龄，横跨两种相距 2 公里的森林类型：低海拔的花旗松和黑松混合森林和高海拔的林线森林占主导地位白皮松。1664 年、1706 年、1785 年、1804 年、1846 年和 1900 年，低海拔森林发生了火灾，平均火灾重现间隔为 47 年。1804 年和 1900 年的火灾也记录在海拔较高的森林中，在 1900 年的火灾中，高海拔地区的树木死亡人数显着。两片森林都经过多次老化，几乎没有证据表明树木群落对严重的林分更换事件做出反应。平均而言，火灾后树木的生长增加了，与火灾前的平均值相比，道格拉斯冷杉的平均年轮宽度增加了 39%，而黑松的平均年轮宽度增加了 40%，这表明一些树木死亡可能与低海拔森林火灾有关. 烧伤在低海拔的森林中更为频繁，偶尔能够蔓延到高海拔的白皮林。虽然我们怀疑火灾从低海拔到高海拔的转变发生在干燥年份，但我们没有通过叠加时代分析发现火灾年份与可用气候重建之间的任何关系。20 世纪白皮林的再生记录了这片森林在 1900 年中度火灾事件后的恢复情况。最后，特别是在海拔较低的花旗松森林中，自上次记录火灾（1900 年）以来的时间似乎比历史记录中的任何无火期都长，这表明排除火灾可能会造成景观和斑块的变化- 规模的林分结构，这可能会影响这些森林中未来的火灾行为，尤其是树冠替代火灾的范围。通过叠加纪元分析，我们没有发现火灾年份与可用气候重建之间的任何关系。20 世纪白皮林的再生记录了这片森林在 1900 年中度火灾事件后的恢复情况。最后，特别是在海拔较低的花旗松森林中，自上次记录火灾（1900 年）以来的时间似乎比历史记录中的任何无火期都长，这表明排除火灾可能会造成景观和斑块的变化- 规模的林分结构，这可能会影响这些森林中未来的火灾行为，尤其是树冠替代火灾的范围。通过叠加纪元分析，我们没有发现火灾年份与可用气候重建之间的任何关系。20 世纪白皮林的再生记录了这片森林在 1900 年中度火灾事件后的恢复情况。最后，特别是在海拔较低的花旗松森林中，自上次记录火灾（1900 年）以来的时间似乎比历史记录中的任何无火期都长，这表明排除火灾可能会造成景观和斑块的变化- 规模的林分结构，这可能会影响这些森林中未来的火灾行为，尤其是树冠替代火灾的范围。