Regeneration and precommercial thinning silviculture of boreal mixed stands

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Harvested mixed aspen/spruce stands often result in planted or pre-established conifer seedlings quickly being overtopped by dense vigorous aspen suckers. Significant silvicultural efforts are then required to release the conifer portion and maintain the mixed structure of these stands. The first goal of this study is to assess the response of spruce growing intimately with aspen to two frequently used precommercial thinning treatments (systematic or crop-tree release) in terms of tree and stand productivity for both species, fauna habitat quality and dynamics of carbon sequestration in soils and above- and belowground vegetation. Second, we want to evaluate the role of aspen's communal root system in the response to precommercial thinning and retention harvesting in mixed stands. Indeed, previous research has shown that interconnected root systems of aspen trees play a role in trees' physiological response to environmental changes, and we want to use this knowledge in order to design adapted silvicultural scenarios in a mixedwood forest context. Precommercial thinning choosing to exclusively keep the largest stems, regardless of their spatial distribution, should produce stands with more vigorous larger individual stems, as well as randomly distributed openings to be enriched with spruce seedlings. Also, retention harvesting selecting to keep interspersed aspen stems, by maintaining apical dominance into the communal root system, should reduce the number of aspen suckers produced post-harvest, offering better growing conditions for spruce seedlings requiring less future silvicultural intervention. Results of this research will be easily transferred to forest industry and managers of the Ministère des forêts, de la faune et des Parcs (MFFP), by offering missing information guiding silvicultural choices according to management objectives, whether they mostly focus on conifer or hardwood productivity or both, or on carbon sequestration or the maintenance of a maximum of quality wildlife habitats, or a mix of these. Accordingly we will use results of this research to recommend appropriate management practices for mixed aspen/spruce stands of the boreal forest.