Lumber and wood chips properties of dead and sound black spruce trees grown in the boreal forest of Canada

Abstract

Little attention has been given to changes in wood properties after isolated mortality events, which characterize the gap dynamics of several forest ecosystems. For the forest industry, dead and sound trees may represent a significant source of timber supply, but of potentially lower quality. The main objective of this study was therefore to compare the properties of wood obtained from dead and sound wood (DSW) trees with those from live trees. In total, 162 black spruce trees (Picea mariana (Mill.) BSP) were felled from three sites comprising three states of tree degradation and three diameter classes. In total, 822 pieces of lumber of different dimensions were produced and visually graded. Full-size lumber pieces of 4.3–5.0 m in length (n 1⁄4 343) were tested for wood stiffness and strength in longitudinal static bending. Samples of wood chips and bark were also collected during the production process at a sawmill. Results indicate that DSW trees produced lumber of significantly poorer mechanical properties than live trees. For the same modulus of elasticity (MOE) value, DSW trees have significantly lower modulus of rupture values than those of live trees, especially for MOE values of ,15 GPa. This suggests that the wood of DSW trees is more brittle, a fact that should be taken into account for the production of machine-stress-rated lumber. Moisture content of wood chips was significantly lower in DSW trees, although it remained above the fibre saturation point. The amount of wood fibre attached to the bark was significantly higher in DSW trees. Considering these differences, DSW trees can be expected to provide wood of inferior quality than live trees but which still meet the technical requirements (Barrett and Lau, 1994) for producing structural lumber.