Effects of precommercial thinning on tree growth and lumber quality in a jack pine stand in New Brunswick, Canada

Abstract

A naturally regenerated jack pine (Pinus banksiana Lamb.) trial established in 1966 in New Brunswick was studied to determine how three precommercial thinning intensities (1.22 m × 1.22 m, 1.52 m × 1.52 m, and 2.13 m × 2.13 m) and a control (154 trees in total) affected tree growth and lumber quality. Mild (thinned to 1.22 m) and moderate (1.52 m) thinning had a modest impact on tree growth after 34 years (stand age 59). However, intensive thinning (2.13 m, or 2212 stems/ha) increased tree height by 13.1% compared with the control, whereas tree diameter and merchantable stem volume per tree increased by >20% and >75%, respectively. Yields of No. 2 and Better increased slightly with increasing thinning intensity, but lumber bending properties decreased with increasing thinning intensity. There was, respectively, >20% and >15% difference in lumber strength (modulus of rupture) and stiffness (modulus of elasticity) between the mild (1.22 m) and intensive (2.13 m) thinnings. Intensive precommercial thinning (2.13 m) is recommended for increased volume growth, but rotation age (>59 years) should not be reduced if lumber bending properties are of concern.