Quantifying the Thermal and Permafrost Impacts of a Tundra Wildfire

阿拉斯加是一个以火为主的生态系统，在许多重要方面与美国大陆和加拿大的北部森林不同。阿拉斯加的火灾多发区主要位于内陆北部森林地区。多年冻土分布的不连续性倾向于促进植被类型的马赛克，在最近历史上没有燃烧过的永久冻土区，发育着茂密的易起火的黑云杉和厚厚的有机层。在苏厄德半岛和育空库斯科维姆三角洲没有树木的苔原地区，火灾也以较低的频率发生。尽管起火原因尚不确定，但火灾记录显示，过去50年来，西沃德半岛的火灾数量出现了明显的积极趋势。显然，这些火灾将对地表能量平衡、土壤水分动态和多年冻土热状况产生显著影响，但这些变化及其相互作用在冻土带地区尚未被量化。四年来，PIS在Seward半岛和Ivotuk附近的四个地点运营了许多气象站，并进行了广泛的土壤测量。其中一个空间站在去年秋天的一场严重火灾中被烧毁，造成了毁灭性的仪器损失，同时也提供了一个独特的机会，可以量化地记录火灾后这个系统将如何变化。在几个月内更换了损坏的设备，以保持对烧伤区域几乎连续的测量记录。这项工作将维持目前在该地区运作的六个气象站。这些地点以前记录的重大年度变化需要维护所有站点，以便能够确定火灾引起的变化的特征，而不是气候的时间变化造成的变化。此外，该小组将利用这一机会调查冻土带火灾对地表能量平衡和地下热状况的影响。这些研究将试图刻画烧伤严重程度对短期影响和长期恢复后果的微妙影响。它们将维持一系列气象站，以记录地表能量平衡的变化，并收集现有1平方公里平静网格(其中一半被烧毁)上活动层厚度的分布测量，以便与过去四年收集的测量结果进行比较。他们将用其他分布在地下的湿度和温度测量来补充这些测量，以表征野火的影响，特别是关于烧伤的严重程度。知识价值：尽管人们对世界北部森林地区的野火进行了广泛的研究，但人们对冻土带火灾对当地生态系统、区域气候或永久冻土和水文状况的影响知之甚少。由于厚厚的冻土带垫的绝缘能力，永久冻土层离地表很近。这个系统如何应对如此剧烈的干扰，还没有得到严格的研究。该盆地内现有的气候网络为立即和经济地记录影响和恢复过程提供了基础。鉴于最近气候和水文制度的变化，有关这些过程的定量信息非常重要。更广泛的影响：野火可能是控制北极和亚北极地区陆地表面变化的主要因素。火灾后立即产生的巨大影响是相当明显的，但更长期的影响可能更重要的是它们对区域和全球气候动态的影响。这项研究将记录这些影响，并预测复苏的长期轨迹。这一理解对于动态植被模型的正确参数化和考虑变化的陆地表面的气候模拟至关重要。

Alaska is a fire-dominated ecosystem differing from the northern forests of the continental U.S. and Canada in many important aspects. The fire-prone areas of Alaska are primarily in the interior boreal forest region. The discontinuous nature of the permafrost distribution tends to promote a mosaic of vegetation types with dense forests of fire-prone black spruce and thick organic layers developing in permafrost areas that have not burned in recent history. Fires also occur, on a lower frequency, in the treeless tundra regions of the Seward Peninsula and Yukon Kuskokwim Delta. Although the cause is uncertain, fire records demonstrate a marked positive trend in the numbers of fires over the last 50 years on the Seward Peninsula. It is obvious that these fires will have marked impacts on surface energy balance, soil moisture dynamics and permafrost thermal regime, but these changes and their interactions have not been quantified in tundra regions. The PIs have operated numerous meteorological stations with extensive soil instrumentation in four locations on the Seward Peninsula and near Ivotuk for four years. One of these stations was destroyed in a severe fire last fall, presenting a devastating loss of instrumentation and at the same time, a unique opportunity to document quantifiably how this system will change following a fire. The damaged equipment was replaced within a few months to maintain a nearly continuous record of measurements in the burn area. This work would maintain six meteorological stations currently operating in that area. The significant annual variation previously documented at these sites necessitates maintenance of all stations to permit characterization of changes due to the fire as opposed to those due to temporal variations in climate. In addition, the group will utilize this opportunity to investigate the impacts of tundra fire on the surface energy balance and subsurface thermal regime. These studies will attempt to characterize the subtle influence of burn severity on both short-term impacts and consequences for long-term recovery. They will maintain the series of meteorological stations to document changes in the surface energy balance and collect distributed measurements of active layer thickness on the existing 1 km2 CALM grid (half of which was burned) to enable comparisons with measurements collected during the previous four years. They will supplement these measurements with other distributed measurements of subsurface moisture and temperature to characterize the impacts of wildfire, particularly with respect to burn severity. Intellectual Merit: While wildfires in the boreal forest regions of the world have been extensively studied, little is known about the impacts of tundra fires on the local ecosystem, regional climate or the permafrost and hydrologic regime. The permafrost is quite close to the surface due to the insulative capability of the thick tundra mat. How this system responds to such a drastic disturbance has not been rigorously studied. The existing climatologic network within this basin provides the basis of immediately and economically documenting the impacts and the process of recovery. Quantitative information on these processes is very important in light of the recent changes in climate and hydrologic regimes. Broader Impacts: Wildfire is probably the dominant agent controlling land surface change in Arctic and subarctic regions. The dramatic impacts immediately following a fire are quite obvious, but the longer-term effects are probably more important in their influence upon regional and global climate dynamics. This research will document those impacts and project long term trajectories of recovery. This understanding is critically important for correct parameterization of dynamic vegetation models and the climate simulations that consider a changing land surface.