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Modern departures in fire severity and area vary by forest type, Sierra Nevada and southern Cascades, California, USA

机译：内华达山脉和美国加利福尼亚南部喀斯喀特的森林类型在现代火灾中的严重程度和区域不同

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Acute changes in ecological disturbance regimes can have major consequences for ecosystems and biota, including humans, living within them. Human suppression of fire in the western United States over the last century has caused notable changes to many ecosystems, especially in lower elevation, semiarid forest types dominated historically by fire tolerant taxa like Pinus and Quercus . Recent increases in fire activity in western US forests have highlighted the need for restoration of ecological structure and function, but management targets for restoration in different forest types remain uncertain. Working in the forests of eastern California, we evaluated the direction and magnitude of change in burned area and fire severity between the period prior to Euro‐American settlement (～1500–1850) and the “modern” period (1984–2009). We compared total annual area burned; proportional area burned at low‐moderate severity and high severity; and annual area burned at low‐moderate severity and high severity between the two time periods in seven forest types. We also examined modern trends in fire area and severity. We found that modern rates of burning are far below presettlement levels for all forest types. However, there were major differences between low to middle elevation forests and high elevation forests regarding the components of this departure. Low and middle elevation forests are currently burning at much higher severities than during the presettlement period, and the departure in fire area is overwhelmingly expressed in the low to moderate severity categories; in these forest types, mean annual area of high severity fire is not notably different between the modern and presettlement periods. In higher elevation forests on the other hand, the modern departure in fire area is expressed equally across fire severity categories. Our results underline the critical need for forest and fire restoration in the study area, especially in low and middle elevation forests adapted to frequent, low severity fire. Expanded management of naturally ignited fires for resource benefit is clearly needed, but in many parts of our study area, strategic reduction of forest fuels will likely be necessary before large‐scale restoration of fire becomes ecologically, politically, and financially feasible.
机译：生态扰动制度的急剧变化可能对其中生活的生态系统和生物区（包括人类）产生重大影响。上个世纪以来，人类抑制了美国西部大火，特别是在海拔较低的半干旱森林类型上，造成了许多生态系统的显着变化，这些半干旱森林类型在历史上一直以耐火类群为主导，如 Pinus和 Quercus。美国西部森林最近的火灾活动增加，凸显了恢复生态结构和功能的必要性，但是不同森林类型的恢复管理目标仍然不确定。我们在加利福尼亚州东部的森林中工作，评估了在欧美定居前（〜1500-1850年）至“现代”时期（1984-2009年）之间燃烧面积和火灾严重性变化的方向和幅度。我们比较了每年的总燃烧面积;中低严重度和高严重度燃烧的比例区域;在这两个时间段之间，七种森林类型的年面积和中低度严重度和高度严重度。我们还研究了火灾面积和严重程度的现代趋势。我们发现，对于所有类型的森林，现代的燃烧率都远低于预设的水平。然而，就这次离开而言，中低海拔森林与高海拔森林之间存在主要差异。目前，中低海拔森林的烈度比预设时期要高得多，而中低烈度类别中绝大多数表示着火区的偏离。在这些森林类型中，在现代时期和预置时期之间，高度火灾的年均面积没有显着差异。另一方面，在海拔较高的森林中，火灾严重程度类别中火灾区域的现代偏离被平均表示。我们的结果强调了研究区域对森林和火灾恢复的迫切需求，特别是在适应频繁，低烈度火灾的中低海拔森林中。为了资源利益，显然需要扩大自然点燃的火的管理，但是在我们研究区域的许多地方，在大规模恢复火在生态，政治和财政上可行之前，有必要战略性地减少森林燃料的使用。

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