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: $ 4.37万
• 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: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=754706
• 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，影响着陆地表面-大气相互作用和大尺度环流模式。世界上大约80%的北方森林含有永久冻土层。在北美西北部（NNA），最北端的北方森林生长在从连续到不连续的永久冻土带过渡的相对寒冷的永久冻土带上。在永久冻土带的南部边界，北方森林生长在与当前气候不平衡的相对温暖和薄的永久冻土带地区。在那里，永久冻土的存在是由非生物和生物生态系统特性（例如，地形、植被、雪）驱动的。北半球永久冻土区的变暖速度是全球变暖速度的两倍，但我们对变暖如何影响北方森林生产力以及北方森林如何作为气候系统的一部分发挥作用的理解仍然有限。通过为NNA提供受限的北方森林生产力估算（COPE），通过整合叶片、全树、景观特征和生态系统水平的测量来解决这一知识缺口，以增强地球系统模型（ESMs）中的北方森林生态现实性。COPE的四个增量短期目标（2018-2022）通过五个项目来实现。中心部分是在加拿大西北部沿2000公里纬向永久冻土梯度的四个北方森林站点进行的生态系统水平净碳(C)、水和能量通量、全树水平液通量密度和茎直径变化的持续涡动相关方差（EC）测量。首先，结合稳定碳同位素比率分析和封闭动态室测量，后者将用于了解北方树种水分利用和储存的种间和种内变异，并有助于限制目前由ec引起的北方森林生产力。这些努力将通过重复调查来补充，这些调查将描述植物的功能特征和叶片水平的气体交换变异性，以及沿梯度的永久冻土条件。最后，将基于植物功能特征的概率建模方法应用于社区土地模型（CLM）。根据作为COPE的一部分收集的观测结果，使用改进的CLM版本进行评估，将检验在不同的永久冻土条件控制下，NNA未来北方森林生产力将有明显差异的假设。COPE是对FLUXNET等全球倡议和美国宇航局北极-北方脆弱性实验的重要高纬度贡献。根据加拿大审计长最近的一份报告（2017年10月18日），COPE在制定森林管理适应战略方面具有根本重要性，这是西北地区急需的能力。