Towards a constrained estimate of boreal forest productivity across northwestern North America

对北美西北部北方森林生产力的有限估计

• 批准号: RGPIN-2018-05743
• 负责人: Sonnentag, Oliver
• 金额: $ 2.19万
• 依托单位: Université de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=683684
• 关键词: Towards; constrained; estimate; boreal; forest

Boreal forests constitute an integral component of the climate system, affecting land surface-atmosphere interactions and large-scale circulation patterns. About 80% of the world's boreal forests contain permafrost, perennially cryotic ground. In northwestern North America (NNA), the northernmost boreal forests grow on relatively cold permafrost at the transition from continuous to discontinuous permafrost. Along the southern limit of permafrost, boreal forests occur in areas with relatively warm and thin permafrost in disequilibrium with the current climate. There, permafrost presence is driven by abiotic and biotic ecosystem properties (e.g., topography, vegetation, snow). The permafrost region of the Northern Hemisphere has been warming at twice the global rate yet our understanding of how warming may affect boreal forest productivity, and thus how boreal forests function as part of the climate system, remains limited. By providing a COnstrained boreal forest Productivity Estimate (COPE) for NNA, this knowledge gap is addressed by integrating leaf-, whole tree-, landscape feature-, and ecosystem-level measurements to enhance boreal forest ecological realism in Earth System Models (ESMs). The four incremental short-term objectives of COPE (2018-2022) are addressed through five projects. The central component is ongoing eddy covariance (EC) measurements of ecosystem-level net carbon (C), water and energy fluxes, whole tree-level sap flux density and stem diameter variation measurements at four boreal forest sites along a 2000-km latitudinal permafrost gradient across northwestern Canada. First, in combination with stable C isotope ratio analysis and closed-dynamic chamber measurements, the latter be will used to understand inter- and intra-species variability in boreal tree species water use and storage, and to help constraining present EC-derived boreal forest productivity. These efforts will be complemented by repeat surveys that characterize plant functional trait and leaf-level gas exchange variability, and permafrost conditions along the gradient. Last, a probabilistic plant functional trait-based modeling approach will be adopted and implemented in the Community Land Model (CLM). Using the refined version of CLM evaluated against the observations collected as part of COPE, the hypothesis that there will be pronounced different in future boreal forest productivity across NNA as controlled by different permafrost conditions will be tested. COPE constitutes an important high-latitude contribution to global initiatives such as FLUXNET, and to NASA's Arctic-Boreal Vulnerability Experiment. COPE is of fundamental importance in the development of forest management adaptation strategies, an urgently needed capacity that is lacking in the Northwest Territories according to a recent report by the Auditor General of Canada (October 18th, 2017).

北方森林是气候系统的一个组成部分，影响着地表-大气的相互作用和大规模环流模式。世界上大约80%的北方森林都有永久冻土层，这是一种常年冰冻的地面。在北美西北部（NNA），最北端的北方森林生长在相对寒冷的永久冻土上，从连续的永久冻土过渡到不连续的永久冻土。沿着永久冻土的南部界限，北方森林出现在与当前气候不平衡的相对温暖和薄的永久冻土区。在那里，永久冻土的存在是由非生物和生物生态系统特性驱动的（例如，地形、植被、雪）。北方的永久冻土区一直在以全球速度的两倍变暖，但我们对变暖如何影响北方森林生产力的理解仍然有限，因此北方森林如何作为气候系统的一部分发挥作用。通过为NNA提供约束北方森林生产力估计（科普），通过整合叶，整树，景观特征和生态系统水平的测量来解决这一知识差距，以提高北方森林在地球系统模型（ESM）中的生态现实主义。科普的四个增量短期目标（2018-2022年）通过五个项目实现。核心组成部分是正在进行的涡动协方差（EC）测量生态系统水平的净碳（C），水和能量通量，整个树级液流密度和干直径的变化测量在四个北方森林网站沿着2000公里纬度的永久冻土梯度横跨加拿大西北部。首先，结合稳定的碳同位素比分析和封闭动态室测量，后者将被用来了解种间和种内变异的北方树种水分利用和储存，并帮助限制目前EC衍生北方森林生产力。这些努力将通过重复调查来补充，这些调查描述了植物功能性状和叶片水平气体交换的变化，以及沿着梯度的永久冻土条件。最后，一个基于概率植物功能性状的建模方法将被采用，并在社区土地模型（CLM）中实现。使用改进版本的CLM评估对科普的一部分，收集的意见，假设将有显着的不同，在未来的北方森林生产力在NNA控制不同的冻土条件下进行测试。 科普是对FLUXNET等全球倡议和美国航天局北极-北方脆弱性实验的重要高纬度贡献。科普在制定森林管理适应战略方面具有根本重要性，根据加拿大审计长最近的一份报告，西北地区缺乏迫切需要的能力（2017年10月18日）。