Variation in black spruce (Picea mariana (Mill.) BSP) wood quality after thinning

Abstract

Commercial thinning (CT) could contribute to increase short-term tree growth and be beneficial in a cold climate, as in boreal regions. Thus, growth rate, ring density and flexural modulus of elasticity (MOE) of trees may change after CT. Moreover, mechanical wood properties vary with position in the tree, and there is a need to develop optimal log allocation strategies in order to allocate logs to their best use. The objectives of the study were to evaluate the impact of commercial thinning on the lumber quality of nine thinned stands compared with unthinned stands and to determine whether this impact varies longitudinally along the first 4 m of the stem. Despite a significant increase in ring width following thinning (p = 0.0003), annual variations in ring density were subtle. No significant variation in average ring density due to CT was observed (p = 0.5122) after thinning, which may be explained by between-stand variability. Thinning showed no significant effect on flexural MOE over a 10-year period. Moreover, variability in average ring density along the stem with tree height was greater than that induced by thinning. A significant decrease in ring density was observed up the stem (from 490 to 463 kg m−3 up to the fourth metre, p < 0.0001). Because it induced increased growth without negative effects on wood mechanical properties, thinning is advisable for slow growth naturally regenerated black spruce stands in the northern boreal region.