Sapling recruitment and mortality dynamics following partial harvesting in aspen-dominated mixedwoods in eastern Canada
Forest Ecology and Management
Boreal mixedwood management has shifted from a relatively narrow focus on commercial wood supply to greater consideration of the natural dynamics and multiple ecological services. This recognition has generated interest in ecosystem management approaches that include diversifying and adapting silvicultural practices, including partial harvesting. The effects of partial harvesting on stand dynamics was assessed over a 12-year period in trembling aspen (Populus tremuloides Michx.) dominated stands in northwestern Quebec, Canada. Four treatments were tested: clearcuts (100% basal area (BA) removal); 1/3 partial cut (1/3 PC, 33% BA removal using low thin); 2/3 partial cut (2/3 PC, 61% BA removal using high thin) and controls (0% removal). Aspen sapling recruitment was directly affected by harvesting intensity with 1/3 and 2/3 partial cuts generating 5% and 56%, respectively, of aspen sapling densities in clearcuts. Aspen sapling recruitment increased continuously following clearcut and partial cut treatments with no significant mortality in the sapling layer over the 12-year period. Recruitment of conifer saplings also increased with time and was significantly higher in the two partial cuts than in the clearcut treatment. Twelve years after treatments, mortality of residual aspen stems (⩾10 cm DBH) reached 250 stems ha−1 12 yr−1 in controls, compared to 106, and 170 stems ha−1 12 yr−1 in 1/3 PC, and 2/3 PC stands, respectively. Initially (1–3 years after treatments), higher overstory aspen mortality was associated with the 2/3 PC treatment. Aspen mortality was strongly associated with small-sized merchantable stems (10–19.9 cm DBH) regardless of treatment. Both partial harvesting treatments had the effect of maintaining mountain maple (Acer spicatum Lamb.), a shade-tolerant, high woody shrub, at densities similar to those in control stands whereas recruitment of mountain maple saplings was negligible in clearcuts due to high aspen recruitment. Our results indicate that (i) heavy-high partial harvesting promotes sapling recruitment of both aspen and conifers when advance regeneration of the latter is present, (ii) because aspen sucker response can be controlled by varying harvesting intensities and stem selection, it is possible to create a range of mixedwood conditions, depending on whether mixed, structurally complex or more regular aspen-dominated stands are desired, and (iii) on rich mixedwood sites, tall woody shrubs could hinder desirable partial harvesting outcomes.
Bose, A.K., BD Harvey, S. Brais. 2014. Sapling recruitment and mortality dynamics following partial harvesting in aspen-dominated mixedwoods in eastern Canada. Forest Ecology and Management 329:37-48