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

北方森林覆盖了北极圈以上植被面积的40%，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，因此火灾制度的变化可能会改变全球碳循环。火灾活动的增加将增加向大气中排放的碳，对气候变暖有潜在的积极反馈。然而，改变的火情也可能对森林再生和永久冻土退化产生级联效应，从而放大或抵消这种反馈。火灾对这些生态机制的影响仍不确定，但最终将决定北极生态系统在未来气候变化情景下是作为碳源还是碳汇。本研究的主要目的是通过阐明火灾严重程度增加对演替间隔内碳积累和储存的影响的生态机制，增加我们对西伯利亚北极北方森林火灾后碳动态的理解。总体假设认为，火灾后土壤有机层（SOL）深度作为种子萌发的屏障和热调节剂，通过间接影响森林再生和永久冻土稳定性来调节生态系统净碳平衡（NECB）。团队将：1)在2012年建立的实验燃烧样地中，将近期火灾对土壤SOL深度的影响与落叶松补充和多年冻土特征的变化联系起来；2)确定火灾后林分结构与不同林分年龄和地形位置的局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测，测试火灾驱动的林分密度变化间接影响苔藓生长的机制。深层碳库对变暖、分解和释放到大气中的敏感性。这项研究将对北极生态系统中植被和土壤过程的重要性提供新的见解，以确定火灾加剧对气候系统的净反馈。智力优势：西伯利亚北极地区的落叶松森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，它们由一个单一的树属（落叶松属）组成，具有落叶生长习性，通常生长在连续的富含碳的叶面上。永久冻土。因此，它们对气候变暖和火灾变化的反应可能不同于其他地区的北方森林。目前西伯利亚寒带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。这项拟议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，并为扩大北极碳库、估计北极火灾的碳排放以及校准未来全球碳循环的预测模型提供必要的数据。更广泛的影响：该项目将培养来自两所主要本科院校和一所西班牙裔服务机构的本科生和研究生。PI和她的学生将与德克萨斯州南部当地的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，并让研究人员在科学课堂上进行演讲，提供北极研究的真实例子，让K-12学生接触到科学领域不同的职业和教育途径。

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.