No 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.

This paper examined the impact of commercial thinning on selected wood properties of jack pine (Pinus banksiana Lamb.). Wood properties evaluated include wood density (ring density, earlywood ring density, and latewood ring density), percentage of latewood in the ring, and wood bending properties. Nonlinear, mixed-effect models have been developed using data from three commercially thinned sites in eastern Canada. Ring density followed the same pattern as percentage of latewood, in which cambial age, relative height, and ring width were found to have important effects. Earlywood and latewood ring densities changed within the juvenile wood zone until a plateau was reached. Ring width affected earlywood and latewood ring densities mainly in narrow rings. Wood bending stiffness (measured by modulus of elasticity) and strength (measured by modulus of rupture) increased with cambial age and wood density; whereas, wood strength was also affected by ring width. Commercial thinning did not influence the developed models, but it had an indirect effect through increased ring width.Résumé : Cette étude a examiné l'impact de l'éclaircie commerciale sur certaines propriétés du bois de pin gris (Pinus banksiana Lamb.). Ces propriétés incluaient la densité du bois (densité des cernes, densité du bois initial et densité du bois final), la proportion de bois final dans chaque cerne et les propriétés mécaniques en flexion. Des modèles non liné-aires mixtes ont été développés à partir de données provenant de trois stations qui avaient subi une éclaircie commerciale dans l'est du Canada. La densité des cernes s'est révélée être fortement influencée par l'âge cambial, la hauteur relative et la largeur des cernes, suivant ainsi un patron de variation similaire à celui de la proportion de bois final. La densité du bois initial et celle du bois final ont changé à l'intérieur de la zone de bois juvénile pour atteindre un plateau par la suite. La largeur des cernes a aussi affecté ces densités, en particulier dans le cas des cernes étroits. Les modules d'élasticité (MOE) et de rupture (MOR) en flexion ont augmenté avec l'âge cambial et la densité du bois. De plus, le module de rupture a été affecté par la largeur des cernes. L'éclaircie commerciale n'a pas changé les paramètres des modèles, mais elle a eu une influence indirecte à cause de son effet sur la largeur des cernes.[Traduit par la Rédaction]