Collaborative Research: Regional impacts of increasing fire frequency on carbon dynamics and species composition in the boreal forest

北极变暖的速度比世界上任何其他地区都要快，其北方森林的火灾规模和频率都急剧增加。这些变化的速度之快引起了人们的关注，因为北方森林占全球森林总量的三分之一左右，含有世界上近一半的碳储存，并且在过去的6,000年里，黑云杉在这一景观中占主导地位。预计到世纪末，气温将上升2-8 °C，新的火灾状况的出现有可能破坏这一森林生态系统。例如，在阿拉斯加内陆的一些地区，火灾复发的间隔已经减少到10-50年，导致从黑云杉到落叶树和草的转变。气候和火灾状况的变化预计也会影响全球碳循环，因为火灾和冻土（永久冻土）的融化可能会将大量碳释放到大气中。这项研究将结合实地研究和计算机模拟，以确定火灾频率和气候变化如何影响植被类型之间的变化（例如从针叶树到草的转换）和长期碳储存在这个广阔和研究不足的地区。这项研究将培训研究生，并让来自阿拉斯加农村荣誉研究所（RAHI）的美国土著高中生参与实地工作。研究人员将与你的世界岩石（YWR）合作，这是一个由女性科学家和工程师组成的非营利组织，致力于促进小学的科学教育。他们将开展以气候变化、森林和火灾为重点的实践活动，并在大波特兰/温哥华都会区的小学开展免费实践活动，特别关注服务不足的1级学校。过去几十年来，北方纬度地区气候变暖的速度很快，火灾频率增加，这引起了人们对植被的重大变化以及生态系统捕获和储存碳的长期能力的担忧。北方森林生态系统约占全世界所有森林的33%，约占世界碳储量的45%，其中大部分（约85%）储存在地下。在过去的6,000年里，黑云杉（Picea mariana（Mill.）B.S.P.）在这片土地的大部分地区都是占优势的物种，对气候变化表现出很强的适应能力。然而，在过去60年中，前所未有的变暖（导致积雪融化提前，永久冻土融化和生长季节延长）和新的火灾制度的出现可能会破坏黑云杉的现有优势，并将全球大量的碳释放到大气中。本研究的目标是通过将机械现场和实验室工作与动态，空间明确的景观建模相结合，量化由于气候变化和反复野火导致的北方森林中碳（C）汇强度，C库存和植被大规模变化的潜力。在阿拉斯加中部工作，研究人员将：1）确定火灾频率和气候变化如何影响演替轨迹和地上和地下C循环，2）评估导致植被类型（即针叶树，硬木，禾本科）和C固存（即汇，源）之间的临界点的机制如何在空间和时间上变化。为了实现这些目标，调查人员将凭经验测量地上和地下的碳储量，生产力，异养呼吸，土壤温度和水分含量，并在该领域的活动层厚度和量化C矿化使用实验室土壤培养。他们还将为广泛使用的高分辨率景观模拟模型（LANDIS-II）开发和验证一个基于物理的永久冻土/水文模块，以预测物种组成和C源/汇状态的长期动态，考虑到气候（包括融化的永久冻土）和火灾的预计变化。这项工作将提高我们对北方森林中碳循环和物种组成如何在精细空间尺度上应对气候变化和干扰的理解，这些空间尺度对准确预测北方森林的未来至关重要。

The Arctic is warming faster than any other area of the world and its boreal forests have experienced dramatic increases in the size and frequency of fires. The fast pace of these changes has prompted concern because boreal forests make up about a third of all forests worldwide, contain almost half of the world's stored carbon, and have been historically stable with black spruce dominating this landscape for the past 6,000 years. Warming of 2-8 °C is projected by the end of the century and the emergence of a new fire regime threatens to disrupt this forest ecosystem. For example, in some regions of interior Alaska, the fire return interval has decreased to 10-50 years, causing shifts from black spruce to deciduous trees and grasses. Changes in the climate and fire regime are also expected to affect global carbon cycling since fires and thawing of frozen soils (permafrost) may release large amounts of carbon into the atmosphere. This research will incorporate field studies and computer simulations to determine how fire frequency and climate change affect shifts between vegetation types (e.g. switch from conifer to grasses) and long term carbon storage in this vast and under-studied region. The study will train graduate students and involve Native American high school students from the Rural Alaska Honors Institute (RAHI) in field work. The investigators will collaborate with Your World Rocks (YWR), a nonprofit organization of female scientists and engineers dedicated to promoting science education in elementary schools. They will develop hands-on activities focusing on climate change, forests, and fire and conduct free hands-on activities in elementary schools in the greater Portland/Vancouver metro area, with a particular focus on underserved Title 1 schools. The fast pace of climate warming and an increase in fire frequency over the past few decades in northern latitudes has raised concerns about major shifts in vegetation and the long-term ability of ecosystems to capture and store carbon. Boreal forest ecosystems account for about 33% of all forests worldwide and contain about 45% of the world's carbon stocks, with the majority (~85%) stored belowground. For the past 6,000 years, black spruce (Picea mariana (Mill.) B.S.P.) has been the dominant species over a large proportion of this landscape, exhibiting substantial resilience to changes in climate. However, unprecedented warming (causing earlier snowmelt, permafrost thawing, and longer growing seasons) and the emergence of a new fire regime over the past 60 years threatens to disrupt the existing dominance by black spruce and release globally significant amounts of carbon into the atmosphere. The goal of this research is to quantify the potential for large-scale changes in carbon (C) sink strength, C stocks, and vegetation in boreal forests due to climate change and repeated wildfires by integrating mechanistic field and lab work with dynamic, spatially explicit landscape modeling. Working in central Alaska, the investigators will: 1) determine how fire frequency and climate change affect successional trajectories and above- and belowground C cycling, and 2) assess how the mechanisms that cause tipping points between vegetation types (i.e. conifer, hardwood, graminoid) and C sequestration (i.e. sink, source) vary spatially and temporally. To achieve these objectives, the investiagors will empirically measure above- and belowground C stocks, productivity, heterotrophic respiration, soil temperature and moisture content, and active layer thickness in the field and quantify C mineralization using laboratory soil incubations. They will also develop and validate a physically based permafrost/hydrology module for a widely-used, high resolution landscape simulation model (LANDIS-II) to forecast long-term dynamics of species composition and C source/sink status given projected changes in climate (including thawing permafrost) and fire. The work will improve our understanding of how C cycling and species composition in boreal forests will respond to climate change and disturbances at the fine spatial scales critical to accurately project the future of the boreal forest.