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

合作研究：火灾频率增加对北方森林碳动态和物种组成的区域影响

• 批准号: 1737166
• 负责人: Vladimir Romanovsky
• 金额: $ 15.02万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1737166&HistoricalAwards=false
• 关键词: Collaborative; Research; Regional; impacts; increasing

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.

北极变暖的速度比世界上任何其他地区都快，其北方森林的火灾规模和频率急剧增加。这些变化的速度之快引起了人们的关注，因为北方森林约占全世界森林的三分之一，含有世界上几乎一半的碳储存量，而且在过去的 6,000 年里一直以黑云杉为主，历史上一直保持稳定。预计到本世纪末气温将升高 2-8°C，而新的火灾状况的出现可能会破坏该森林生态系统。例如，在阿拉斯加内陆的一些地区，火灾重现间隔已缩短至 10-50 年，导致黑云杉转变为落叶乔木和草丛。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）的融化可能会向大气中释放大量碳。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这个广阔且研究不足的地区植被类型之间的转变（例如从针叶树到草的转变）和长期碳储存。该研究将培训研究生，并让阿拉斯加乡村荣誉学院 (RAHI) 的美国原住民高中生参与实地工作。研究人员将与 Your World Rocks (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中开展免费实践活动，特别关注服务不足的 Title 1 学校。过去几十年来，北纬地区气候变暖的快速步伐和火灾频率的增加引起了人们对植被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球所有森林的 33%，包含约 45% 的世界碳储量，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.) 一直是该地区大部分地区的优势树种，对气候变化表现出强大的适应能力。然而，过去 60 年来前所未有的变暖（导致融雪提前、永久冻土融化和生长季节延长）和新火势的出现，有可能破坏黑云杉现有的主导地位，并向大气中释放全球大量碳。本研究的目标是通过将机械现场和实验室工作与动态、空间明确的景观模型相结合，量化气候变化和反复野火导致北方森林碳（C）汇强度、碳储量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以及地上和地下碳循环，2）评估导致植被类型（即针叶树、硬木、禾本科）和碳封存（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，研究人员将凭经验测量地上和地下碳储量、生产力、异养呼吸、土壤温度和水分含量以及田间活性层厚度，并使用实验室土壤孵化来量化碳矿化。他们还将开发和验证基于物理的永久冻土/水文模块，用于广泛使用的高分辨率景观模拟模型（LANDIS-II），以根据预计的气候变化（包括永久冻土融化）和火灾来预测物种组成和碳源/汇状态的长期动态。这项工作将提高我们对北方森林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，这对于准确预测北方森林的未来至关重要。