Collaborative Research: Fire regime influences on carbon dynamics of Siberian boreal forests

北方森林覆盖了北极圈以上40%的植被覆盖面积，是北极生态系统的重要组成部分。全球变化模型预测，随着气候变暖，北方森林将变得越来越容易受到火灾活动的影响。由于这些森林包含了全球陆地碳（C）储量的很大一部分，火灾制度的变化可能会改变全球C循环。火灾活动的增加将增加碳排放到大气中，对气候变暖有潜在的积极反馈作用。然而，改变的火灾制度也可能引发对森林再生和永久冻土退化的级联效应，这可能会放大或抵消这种反馈。火灾对这些生态机制的影响仍然不确定，但最终将决定北极生态系统是否作为碳源或汇在未来的气候变化情景。本研究的主要目的是增加我们的理解火灾后的C动态在西伯利亚北极的北方森林的生态机制，通过阐明火灾的严重程度增加可能会影响C积累和存储的演替间隔。总体假设是，火灾后土壤有机层（SOL）深度调节净生态系统碳平衡（NECB）通过间接影响森林再生和永久冻土的稳定性，因为它的作用作为种子萌发和热调节的障碍。该小组将：1）将近期火灾对SOL深度的影响与2012年创建的实验燃烧地块中落叶松补充和永久冻土特征的变化联系起来，2）确定火灾后林分结构与不同年龄和地形位置的林分在当地和景观水平上的地上和地下C库之间的关系，3）通过实验操作和野外观察，测试火驱动的林分密度变化间接影响苔藓生长、SOL发展和深层C库对变暖、分解并释放到大气中。这项研究将为北极生态系统内的植被和土壤过程在确定火灾加剧对气候系统的净反馈方面的重要性提供新的见解。学术价值：西伯利亚北极的落叶松林占所有北方森林生态系统的20%，与其他北方森林不同的是，它们由单一的树属（落叶松属）组成。具有落叶生长习性，经常连续生长，碳含量丰富？yedoma？永久冻土因此，它们对气候变暖和火灾状况改变的反应可能不同于其他地区的北方森林。目前西伯利亚北方森林中碳库的不确定性仍然是影响我们预测气候引起的全球碳循环变化能力的一个重要因素。拟议中的研究将有助于我们了解北极森林火灾如何影响全球碳循环，并提供必要的数据，扩大北极碳池，估计碳排放量从北极火灾，并校准未来的全球碳cycling.Broader影响预测模型：该项目将导致本科生和研究生的培训，从两个主要的本科院校和一个西班牙裔服务机构。PI和她的学生将与德克萨斯州南部的当地K-12学校开展外展活动，帮助教师制定涉及北极科学，北方生态学和气候变化的课程计划，并将研究人员介绍到科学教室，以提供北极研究的真实例子，并使K-12学生接触科学中不同的职业和教育路径。

Boreal forests cover 40% of the vegetated land area above the Arctic Circle and are a critical component of arctic ecosystems. Global change models predict boreal forests will become increasingly susceptible to fire activity with climate warming. Because these forests contain a large proportion of global terrestrial carbon (C) stocks, changes in the fire regime are likely to alter global C cycling. Increased fire activity will increase C emissions to the atmosphere, with a potential positive feedback to climate warming. However, an altered fire regime may also initiate cascading effects on forest regrowth and permafrost degradation that could magnify or offset this feedback. Fire effects on these ecological mechanisms remain uncertain but will ultimately determine whether arctic ecosystems act as a C source or sink under future climate change scenarios. The primary objective of this research is to increase our understanding of post-fire C dynamics in boreal forests of the Siberian arctic by elucidating the ecological mechanisms by which increased fire severity could influence C accumulation and storage over the successional interval. The overarching hypothesis is that post-fire soil organic layer (SOL) depth regulates net ecosystem carbon balance (NECB) through indirect impacts on forest regrowth and permafrost stability because of its role as a barrier to seed germination and thermal regulator. The team will: 1) link near term fire effects on SOL depth to changes in larch recruitment and permafrost characteristics in experimental burn plots created in 2012, 2) determine the relationship between post-fire stand structure and above- and belowground C pools at the local and landscape level across stands of varying age and topographic positions, and 3) test via experimental manipulations and field observations the mechanisms by which fire-driven changes in stand density indirectly affect moss growth, SOL development, and susceptibility of deeper C pools to warming, decomposition, and release into the atmosphere. This research will offer novel insights into the importance of both vegetation and soil processes within arctic ecosystems in determining the net feedback of an intensified fire regime to the climate system.Intellectual Merit: Larch forests of the Siberian arctic comprise 20% of all boreal forest ecosystems and are distinct from other boreal forests in that they consist of a single tree genus (Larix spp.) with a deciduous growth habit and often grow on continuous, C-rich ?yedoma? permafrost. Thus, their response to warming climate and an altered fire regime is likely to differ from boreal forests in other regions. Uncertainties regarding current C pools in Siberian boreal forests remain a significant factor affecting our ability to predict climate-induced changes to the global C cycle. The proposed study will contribute to our understanding of how arctic forest fires impact global C cycling and provide essential data necessary for scaling-up arctic C pools, estimating C emissions from arctic fires, and calibrating predictive models of future global C cycling.Broader Impacts: This project will result in the training of undergraduate and graduate students from two predominantly undergraduate institutions and one Hispanic-Serving Institution. The PI and her students will develop outreach activities with local K-12 schools in south Texas to help teachers create lesson plans involving arctic science, boreal ecology, and climate change and involve researcher presentations to science classrooms to provide real-life examples of arctic research and expose K-12 students to different career and educational paths in the sciences.