Impact of the white pine weevil (Pissodes strobi [Peck]) on Norway spruce (Picea abies [L.] Karst.) plantations. Part 2: Lumber properties

Abstract

We studied the lumber characteristics of 148 trees acquired for that purpose during commercial thinning operations in three Norway spruce (Picea abies [L.] Karst.) plantations, aged from 32 to 34 years, which had been attacked repeatedly by the white pine weevil (Pissodes strobi [Peck]). The trees, with diameters ranging from 14 to 23 cm, were grouped into three quality classes according to the number of major deformations caused by the weevil. The effects of the deformations on bending strength and stiffness, wood density and lumber defects were examined. Results show that in general deformations caused by the weevil do not affect the lumber properties of Norway spruce on sites of medium to high quality. For the three Norway spruce plantations, the mean values of the modulus of elasticity (MOE) of the lumber varied between 8510 and 9357 MPa, and for the modulus of rupture (MOR) they ranged from 36.0 to 42.5 MPa, whereas wood density varied from 324 and 343 kg·m-3. For comparison purposes, the same measurements were taken on lumber from 38 trees in a white spruce (P. glauca [Moench] Voss) plantation that was unaffected by the weevil, but comparable to the Norway spruce plantation on one of the sites studied. The lumber properties from Norway spruce taken from deformed or undeformed stems were 34% superior to white spruce for MOE, 20% for MOR and 8% for wood density. The smaller knots in Norway spruce could explain this difference. On the other hand, a visual grading of this type of wood reveals few differences in lumber strength and stiffness.