Geomorphic Impacts of Catastrophic Fire in Ponderosa Pine Ecosystems: Modern and Holocene Perspectives from Granitic Mountains of Central Idaho

[00:90 . 05]近几十年来，林冠大火席卷了美国西部半干旱的黄松林。在爱达荷州中部，大约300年的树木年轮记录表明，20世纪初，低强度地表火灾的频率急剧下降，这表明灭火和燃料堆积是最近灾难性火灾的主要原因。然而，人们对气候变化在改变火灾制度中的作用知之甚少。加剧的燃烧和随之而来的斜坡侵蚀也可能是上个世纪气候变暖的一个症状，导致了异常严重的干旱和强烈的对流风暴。因此，最近的冠层火灾、斜坡侵蚀和黄松林的泥石流在冰川后历史中真的是例外吗？过去这些事件发生的频率和强度是多少？严重火灾和斜坡侵蚀的频率是否随着全新世气候变化而改变？我们将通过爱达荷州中部帕耶特河流域众多小型冲积扇的全新世地层记录来解决这些问题。最近来自燃烧盆地的泥石流和洪水事件使得在扇地层剖面中区分与火灾有关的沉积物的相模型得以发展。被烧毁的土壤表面提供了明确的地层标记和准确的火灾日期，与火灾有关的泥石流沉积物是强烈的树冠火灾和地貌反应的可确定的证据。大量的14C年代数据将估算出与火灾有关的沉积事件随时间和空间变化的概率和频率。沉积斜坡沉积物和主要河流活动的定年将与冲积扇记录相结合，以便对全新世地貌对火灾、气候变化和内在控制的反应进行全面的全系统分析。它还将为了解黄松生态系统的火灾制度和山区环境中的自然灾害提供长期背景。

0000905MeyerIn recent decades, large canopy fires have swept through ponderosa pine forests of the semi-arid western United States. In central Idaho, ~300-year tree-ring records indicate a dramatic decrease in the frequency of low-intensity surface fires in the early 1900s, suggesting that fire suppression and fuel buildup due are largely responsible for recent catastrophic burns. The role of climatic variations in changing fire regimes, however, is much less understood. Intensified burning and ensuing slope erosion might also be a symptom of climatic warming over the last century, leading to unusually severe droughts and intense convective storms. Thus, are recent canopy fires, slope erosion, and debris flows in ponderosa pine forests truly exceptional in postglacial history? What has been the frequency and magnitude of these events in the past? And, has the frequency of severe fires and slope erosion changed in response to Holocene climatic variations?We will address these questions through the Holocene stratigraphic record in numerous small alluvial fans in the Payette River drainage of central Idaho. Recent debris-flow and flood events from burned basins allow development of facies models for distinguishing fire-related sediments in fan stratigraphic sections. Burned soil surfaces provide unambiguous stratigraphic markers and accurate fire dates, and fire-related debris-flow deposits are datable evidence of both intense canopy fires and geomorphic response. A large set of 14C dates will yield estimates of the probability and frequency of fire-related sedimentation events over time and space. Dating of colluvial slope deposits and mainstem fluvial activity will combine with alluvial fan records to allow comprehensive system-wide analysis of Holocene geomorphic response to fire, climatic change, and intrinsic controls. It will also provide a long-term context for understanding fire regimes in ponderosa pine ecosystems and natural hazards in mountain environments.