Lumber volume and value yields of balsam fir trees affected or killed by the spruce budworm in the northeastern boreal forest of Canada

Abstract Spruce budworm ( Choristoneura fumiferana (Clemens)) is the most destructive native forest defoliating insect in North America. Repeated defoliation causes tree mortality over large areas, reducing timber supply and wood quality. Since trees do not all die at the same time, the challenge for the wood transformation industry is to know if dead trees are worth salvaging. The objective of this study was to compare visual lumber grade yield and value extracted from live and dead balsam fir trees in three different states of degradation, based on Hunter classes 2 (live but declining trees), 3 (recently dead trees) and 4 (dead trees with bark peeling off). A total of 92 balsam fir trees were felled on five sites located in the Quebec North Shore region. The trees yielded 354 sawlogs, which were processed into 1044 pieces of lumber. All products were graded visually according to National Lumber Grades Authority (NLGA) standards. Results showed a major loss in wood quality following tree death, with a significant decrease in the volume proportion of high-quality Select Structural and No. 2 lumber grades (No. 2 and Better) from 51% in Hunter class 2 to 32% in class 3 and 13% in class 4, and a notable increase of low-quality No. 3 lumber from 25% in Hunter class 2, 36% in class 3, and 63% in class 4. Decay was the most important downgrading defect for the three Hunter classes, accounting for 22% of the lumber volume produced in class 2, 39% in class 3, and 69% in class 4. Lumber values per tree and per volume (m 3 ) significantly decreased from Hunter class 2 to 4. Compared to Hunter class 2, total lumber value dropped by 13% for class 3 and 34% for class 4 when grading lumber according to NLGA Para. 124 (Structural), and by 13% and 27% when grading the same lumber as Stud (NLGA Para. 121), indicating that the use of NLGA 121 helps reduce value losses in degraded dead trees. Based on these results, Hunter class 3 trees can still be harvested as their lumber value is close to that of live but declining class 2 trees, while trees of the most degraded class (4) may not be economically suitable to salvage, as wood degradation caused a major drop in lumber quality and value, especially in the largest diameter trees (29–33 cm).