A sustainable forest management system requires that a balance must be reached between ecosystem nutrient losses and gains in the course of a rotation. In order to determine the influence of stand characteristics (species composition, density, site potential productivity), method of forest harvesting (stem-only versus whole-tree) as well as rotation length on nutrient losses induced by biomass harvesting, a geochemical balance (nutrient inputs minus outputs) was computed from published information and forest inventory databases for the southern portion of the boreal forest of Quebec. Losses were compared with potential nutrient gains that varied according to soil types. We provided a tool for assessing the risk of having a negative nutrient budget (outputs>inputs ) that forest managers can use with information that is already available to them. This exercise was conducted for five commercial tree species, namely paper birch (Betula papyrifera Marsh.), aspen (Populus tremuloides Michx.), balsam fir (Abies balsamea (L.) Mill.), jack pine (Pinus banksiana Lamb.), and black spruce (Picea mariana (Mill.) B.S.P.), grouped into four site indexes and three stand density classes. Strong differences in nutrient exportation in biomass appeared between stands of different compositions as well as between stands of the same species but of different classes of productivity or density. The most nutrient-demanding tree species were trembling aspen and balsam fir. As expected, whole-tree harvesting caused a greater drain on nutrient reserves than stem-only harvesting, but this effect varied strongly with tree species and was greatest for balsam fir and lowest for jack pine. Harvesting the forest before or after the age of financial maturity, which might be desirable under some circumstances, generally created a lesser nutrient drain but this was at the expense of biomass production. Aspen was an exception to this rule showing a greater nutrient drain for stands harvested prior to the age of financial maturity. Implications for the development of indicators of sustainable forestry and for future research are discussed.

Concerns over decreases in soil nitrogen reserves and productivity following the removal of logging residues (windrowing, shearblading and piling.) have been raised by numerous researchers. Medium-term impacts of this practice on soil N reserves and availability and on indices of organic matter quality were assessed for balsam fire (Abies balsamea (L.) Mill.), white birch (Betula paperyfera Marsh.) and white spruce (Picea glauca (Moench) Voss) stands growing on dry to fresh clayey sites in northwestern Quebec, Canada. Unharvested control stands, whole-tree harvested cutovers. and windrowed sites were compared. Fifteen years following harvesting and windrowing, forest floor Kjeldahl N concentrations and content and forest floor in situ net N mineralization rates (undisturbed closed top cores incubation) were affected by harvesting but not by windrowing. No differences in mineralization constant, potentially mineralizable N and cumulative mineralized N (526 day incubation period) were found between treatments, suggesting that treatment differences in field net N mineralization rates were the result of interactions between residual ecosystem structures such as forest floor. coarse woody debris and vegetation and meteorological conditions. If these trends persist over time, it could signal that, while whole-tree harvesting does not have a direct effect on soil organic matter quality, long-term impacts on N dynamics could result from changes in ecosystem structures. Slash removal following whole-tree harvesting did not have any additional negative impact. (C) 2002 Elsevier Science B.V. All rights reserved. © 2002 Elsevier B.V. All rights reserved.