Modelling Carbon Dynamics of Boreal Forest Ecosystems Using the Canadian Land Surface Scheme

The ecosystem carbon (C) and nitrogen (N) simulations recently implemented in the Canadian Land Surface Scheme (CLASS) are presented. The main calculations include plant photosynthesis, autotrophic respiration, root N uptake, litterfall, plant growth, and soil heterotrophic respiration. Model experiments are made on two boreal forest ecosystems, deciduous (aspen) and conifers (black spruce). Simulated plant, soil, and ecosystem CO₂ exchanges are analysed on half-hourly, daily, and annual time scales and compared with tower eddy correlation flux measurements and estimates from various authors. Modeled daily ecosystem CO₂ exchange explained86% and 54%, respectively, of the observed variance of eddy correlationflux at the aspen site and at the black spruce site. Annual results show that the aspen ecosystem was simulated as a C sink in both 1994 (+164 g Cm^–2) and 1996 (+142 g C m^–2), and the black spruce ecosystem wassimulated as a C sink in 1994 (+39 g C m^–2) and 1995 (+25 g Cm^–2), but as a C source in 1996 (–27 g C m^–2).