Growth and wood quality of black spruce and balsam fir following careful logging around small merchantable stems (CLASS) in the boreal forest of Quebec, Canada

Abstract

Careful logging around small merchantable stems (CLASS) is a partial cutting treatment in which 70–90 per cent of the merchantable volume of uneven-aged, irregular or multi-layered conifer stands is harvested. The decrease in stand density by means of partial cutting is known to induce an increase in residual stem growth, which could also influence wood properties. This research aims to evaluate the effect of CLASS on the growth and some wood quality parameters of black spruce (Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) Mill.) in the boreal forest of Quebec, Canada. Four uneven-aged black spruce-balsam fir stands were selected for the study and 15 black spruce and 15 balsam fir trees were sampled in each stand, distributed between a treated and a control area. Radial growth, latewood proportion, ring density, tracheid length and the moduli of elasticity and rupture were measured in each tree. A high proportion of residual stems significantly increased their radial growth after CLASS. No significant change was obtained for latewood proportion, average ring density, tracheid length or mechanical properties for black spruce. However, latewood proportion and ring density were significantly reduced in balsam fir after treatment, with no effect on modulus of elasticity or modulus of rupture. When looking at the wood properties comprehensively, a canonical discriminant analysis did not detect any significant difference between the wood properties before and after treatment for either species. This suggests that CLASS can stimulate the radial growth of residual stems with limited short-term effects on wood quality.