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

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，当地地形、植被组成和结构、有机层厚度、积雪深度以及土壤温度和湿度）。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提供一个约束北方森林生产力估计（科普），我们将解决这一重要的知识差距，通过整合叶，整棵树，景观特征，和生态系统水平的测量概率植物功能性状为基础的建模方法，以提高北方森林生态现实主义在地球系统模型。该提案要求提供资金，以完成一个独特的仪器设置（连续全年涡度协方差补充液流密度和茎直径变化测量）在五个北方森林网站沿着2000公里的纬度永久冻土梯度横跨加拿大西北部的北方森林：自动周长测树仪，自制的热耗散液流密度探头和微气象站。这些测量是用来了解种间和种内的变化，在北方树种水的利用和储存，并帮助限制生态系统规模的总初级生产力从涡动协方差测量在四个北方森林网站沿着梯度。科普是对美国航天局北极-北方脆弱性实验的重要贡献。此外，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（2017年10月18日），西北地区缺乏迫切需要的能力。

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., local topography, vegetation composition and structure, organic layer thickness, snow depth, and soil temperature and moisture). 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, we will address this important knowledge gap by integrating leaf-, whole tree-, landscape feature-, and ecosystem-level measurements in a probabilistic plant functional trait-based modeling approach to enhance the boreal forest ecological realism in Earth System Models. This proposals asks for funds to complete a unique instrumental set-up (continuous year-round eddy covariance complemented by sap flux density and stem diameter variation measurements) at five boreal forest sites along a 2000-km latitudinal permafrost gradient across the boreal forest of northwestern Canada: automatic circumference dendrometers, self-manufactured thermal dissipation sap flux density probes and micrometeorological stations. These measurements are used to understand inter- and intra-species variability in boreal tree species water use and storage, and to help constraining ecosystem-scale gross primary productivity obtained from eddy covariance measurements made at four boreal forest sites along the gradient. COPE constitutes an important contribution to NASA’s Arctic-Boreal Vulnerability Experiment. In addition, 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).