AbstractsBiology & Animal Science

The circumpolar boreal forest is an extensive carbon (C) reservoir, storing an estimated 88 petagrams (Pg) of C in vegetation biomass with an additional 471 PgC residing within the soil itself. In the North American boreal, fire disturbance acts as the main stand-renewing agent along an approximate 100-year return interval. However, recent studies suggest that fire intensity and severity are increasing, driven by disproportionate climate warming of the northern latitudes. In this study, we examine carbon dioxide (CO2), water vapour and energy exchange in a 7-year old, post-burn, jack pine stand located in the eastern James Bay region of the North American boreal; an area currently under-represented in fire studies. Over 1.5 years, covering two growing seasons and the spring and fall transitions, we measured net CO2 and energy exchange at the ecosystem level using an eddy covariance tower, and supplemented this with chamber measurements of soil respiration. The objectives of this study were to determine the environmental controls on the variability of the mass and energy fluxes. Net ecosystem exchange of CO2 (NEE) over the stand was typically small (-2.3 to 1 gC m-2 d-1), with respect to other young boreal stands, at times flipping between net uptake and release on a day-to-day basis. Annual cumulative NEE was determined to between +7 and -6 gC m-2 y-1, classifying it as approximately carbon-neutral. Cumulative ecosystem respiration and gross ecosystem productivity were smaller on an annual basis compared to other recently disturbed stands. The low productivity was associated with a lower vegetation abundance and LAI at the site due to very dry soil conditions. The increase in latent heat exchange (and decrease in sensible heat exchange) between growing seasons was determined to be primarily moisture-driven, with evaporation the dominant pathway. Little change in summertime albedo between years suggested that deciduous plant growth was not significant at the site. La forêt boréale circumpolaire est un important réservoir de carbone (C) contenant 88 pétagrammes (Pg) de C dans la biomasse végétale et 471 PgC dans le sol lui-même. Dans les secteurs boréaux d'Amérique du Nord, les feux sont les principaux agents de renouvellement des forêts, avec un cycle d'environ 100 ans. De récentes études suggèrent que la sévérité et l'intensité des feux sont en hausse, due aux effets amplifiés des changements climatiques dans les latitudes élevées. La présente étude vise à documenter les échanges de dioxyde de carbone (CO2), de vapeur d'eau et d'énergie dans une forêt dominée par le pin gris (Pinus banksiana), brûlée il y a 7 ans. Le site d'étude est situé à l'est de la Baie James, dans la partie est de la forêt boréale nord-américaine. Cette région est sous représentée en terme d'études sur les impacts des feux de forêts. Durant une période de un an et demi, incluant deux saisons de croissance et les périodes de transitions d'automne et du printemps, nous avons mesuré les émissions nettes de CO2 et d'énergie à l'échelle de…