Potential productivity of aspen cohorts originating from fire, harvesting, and treefall gaps on two deposit types in northwestern Quebec

Height growth of trembling aspen (Populus tremuloides Michx.) stands originating from three different disturbance types (fire, clearcut, and tree-fall gap) was compared on two different deposits (glacial till and lacustrine clay) in the Abitibi region in northwestern Quebec using stem analysis techniques. Several soil properties were also measured to investigate relationships between soil properties and aspen growth. Height growth of aspen was not significantly different among stands of different origins, although on both deposits and at all stages of growth, trees originating from fire were the tallest. Differences in total height among stands of different origins were less than 3 m at 50 years of age. The greatest differences in height growth among stands were expected at younger stages likely because of lower light levels for trees originating from gaps at this stage, but the opposite was observed; height growth differences for 5-year intervals were greater for taller trees. Height growth was greater on clay than on till soils but only for trees greater than 15 m. Soil pH and availability of nitrogen and calcium were correlated with aspen height growth on till soils, while only exchangeable calcium was related to this property on clay soils. Fire had beneficial effects on soils, because it increased soil pH and exchangeable cations. However, these effects did not significantly affect tree growth over one or two rotations.