Wood and Lumber Properties from Unthinned and Precommercially Thinned Black Spruce Plantations

This study examined wood and lumber bending properties of 44-yr-old plantation black spruce subjected to precommercial thinning (PCT) at age 23. PCT and tree diameter at breast height (DBH) had little effect on heartwood content and the No. 2 & Better lumber grade yield. With increasing DBH of 10 - 18 cm, basic wood density (Db), lumber bending modulus of elasticity (MOE), and modulus of rupture (MOR) decreased by 8.1, 15.8 and 19.0%, respectively. The Db, MOE, MOR, and machine stress-rated (MSR) lumber yield from the stand with 35% basal area removal (T35) were lower than those of the control (T0) and the stand with 20% basal area removal (T20). The T20 had no significant effect on the Db, MOE, MOR, and MSR lumber yield. Juvenile wood content had a negative effect on lumber bending properties. The percentage of lumber pieces complying with the design values decreased with increasing thinning intensity. On average, MOE from T0, T20, and T35 were 10.9, 12.1, and 19.5% lower, respectively, than that from mature natural black spruce stands and 19.6, 18.0, and 10.8% higher, respectively, than that from wider-spaced black spruce plantations. MOE from T0 was also 14.5% higher than that from 50 - 60-yr-old natural jack pine stands. This study indicates that it is possible to produce high-quality lumber from dense black spruce plantations with appropriate thinning.