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Abstract: The boreal forest, earth''s second largest terrestrial biome, is currently thought to be an important net carbon sink for the atmosphere. In this study, a newly developed carbon exchange model of TRIPLEX-Flux (with half-hourly time step) is used to simulate the ecosystem carbon exchange of a 75-year-old boreal mixedwood forest stand in northeast Ontario and a 110-year-old pure black spruce stand in southern Saskatchewan, Canada. Results of net ecosystem exchange (NEE) simulated by TRIPLEX-Flux for 2004 are compared with those measured by eddy-flux towers and suggest overall agreement between model simulation and observations. The mean coefficient of determination (R 2) is approximately 0.77 for boreal mixedwood and 0.62 for old black spruce. Differences between model simulation and observation may be attributed to uncertainties not only in model input parameters and calibration, but also in eddy-flux measurements caused by systematic and random errors. The model is able to capture the diurnal variations of NEE for the growing season (from May to August) of 2004 for both sites. Both boreal mixedwood and old black spruce were acting as carbon sinks for the atmosphere during the growing season of 2004. However, the boreal mixedwood stand shows higher ecosystem productivity, carbon sequestration, and carbon use efficiency than the old black spruce stand. [Copyright &y& Elsevier]

Individual-tree models of five-year basal area growth were developed for jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP) in northern Ontario. Tree growth data were collected from long-term permanent plots of pure and mixed stands of the two species. The models were fitted using mixed model methods due to correlated remeasurements of tree growth over time. Since the data covered a wide range of stand ages, stand conditions and tree sizes, serious heterogeneous variances existed in the data. Therefore, the coefficients of the final models were obtained using weighted regression techniques. The models for the two species were evaluated across 4-cm diameter classes using independent data. The results indicated (1) the models of jack pine and black spruce produced similar prediction errors and biases for intermediate-sized trees (12–28 cm in tree diameter), (2) both models yielded relatively large errors and biases for larger trees (> 28 cm) than those for smaller trees, and (3) the jack pine model produced much larger errors and biases for small-sized trees (< 12 cm) than did the black spruce model. [ABSTRACT FROM AUTHOR]

With 2% of the world’s forests and 17% of Canada’s forested land, Ontario plays a major role in maintaining Canada’s forests and managing them sustainably. Ontario is developing a set of criteria and indicators of sustainable forest management (SFM) to aid in conservation and sustainable management of its temperate and boreal (BO) forests. The criteria and indicators are intended to provide a framework for describing and assessing processes of SFM at a regional scale; and to improve the information available to the public and decision-makers. This paper describes three ecological indicators, evaluated using a carbon (C) budget model, a forest inventory database, and disturbance records to assess long-term sustainability of Ontario’s forest ecosystems based on the environmental conditions of the past 70 years. Results suggest that total net primary productivity (NPP) of Ontario’s forest ecosystems increased from 1925 to 1975 and then decreased between 1975 and 1990; Ontario’s forest ecosystems acted as a C sink between 1920 and 1980, and a C source from 1981 to 1990, mainly due to decreased average forest age and NPP caused by increased ecosystem disturbance (e.g. fire, insect and disease infestations, harvesting) since 1975. Current estimates from this analysis suggest that there is significant potential for Ontario’s forests to function as C sinks by reducing ecosystem disturbances and increasing growth and storage of C in the young forests throughout the province. [Copyright &y& Elsevier]