Shelterwood cutting in a boreal mixedwood stand: 10-year effects of the establishment cut on growth and mortality of merchantable residual trees

We used two-step shelterwood cutting to release conifer advance growth and limit development of trembling aspen (Populus tremuloïdes Michx.) suckers in a stratified mixed aspen - conifer stand, in Quebec, Canada. This study presents the 10-year response of residual trees to the establishment cutting. We examined growth and mortality of merchantable trees (diameter at breast height (DBH) ⩾ 9.1 cm) following the application of different cutting intensities (0%, 35%, 50%, 65%, and 100% basal area removal). Initial post-cut densities were 1100, 670, 640, 580 and 150 stems ha−1, respectively. Mortality of aspen was highest in the uncut control and 35% cut due to senescence, while mortality of paper birch (Betula papyrifera Marsh.) was highest in the 65% cut due to post-logging decadence. In the species mixture under study, the 50% cut allowed for the harvest of declining aspen without excessively opening the canopy that would be detrimental for residual paper birch. Low mortality, high recruitment and a relatively high DBH growth in this moderate cut resulted in a higher 10-year net increment in total basal area (7.0 m2 ha−1), compared to the 0%, 35%, 65%, and 100% cuts (2.6-3.7 m2 ha−1). This result was mostly attributable to balsam fir (Abies balsamea (L.) Mill.) that generated two-thirds of the net increment. Therefore, our growth results support retention of small merchantable conifer stems (DBH 9.1-15.0 cm) as a basic strategy to limit hardwood invasion.