Impact du charançon du pin blanc (Pissodes strobi Peck) dans les plantations d'épinettes de Norvège (Picea abies [L.] Karst.) Partie 1 : Productivité et qualité des sciages

Abstract

A study to assess the effects that major deformations in merchantable stems of Norway spruce (Picea abies [L.] Karst.), caused by the white pine weevil (Pissodes strobi [Peck]), have on lumber productivity and quality was performed on logs obtained from the second commercial thinning operation in three weevil-affected plantations. Deformed stems were found to be 6.3% shorter than undeformed stems and their lumber characteristics — merchantable volume, number of board feet and lumber monetary value — were 14.7%, 20.6% and 23.7% lower, respectively. However, when the respective proportions of deformed and undeformed stems were analyzed for a given plantation over a time horizon of a complete rotation, these shortfalls almost disappeared, with a loss of less than 3% being noted for total merchantable volume. The presence/absence of major deformations had no effect on visual grading of the lumber, which considers defects such as wane, knots and compression wood. For two of the three sites studied, almost 75% of the lumber was graded as Select Structural, No. 1 or No. 2. The plantation site and its characteristics (spacing and level of thinning) were found to have a more significant effect than deformations on productivity, lumber quality and monetary value. Furthermore, using the same methodology, one of the Norway spruce sites was compared with a white spruce (Picea glauca [Moench] Voss) plantation containing trees of similar quality and height but no weevil problems. The Norway spruce stems, including those with deformations, were found to yield higher merchantable and usable log volumes, a larger number of board feet and a higher monetary value than the white spruce. On average, for the diameter-at-breast-height values tested — 14 to 23 cm — the monetary value of the lumber was 26% higher for Norway spruce. These findings are largely attributable to the less pronounced taper of Norway spruce. In conclusion, in spite of weevil attacks and its negative impact, Norway spruce trees growing on sites of moderate to very good quality maintain lumber potential, in terms of both quantity and quality for second thinning logs. The negative impact should gradually diminish at the time of next thinnings and final harvest. Key words: white pine weevil, Pissodes strobi (Peck), Norway spruce, Picea abies (L.) Karst., wood quality, plantation, productivity