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

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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).