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Commercial thinning represents one of the treatments used in intensive management to increase the growth of the residual stems. Therefore, commercial thinning would decrease the wood mechanical properties, but the negative effects are temporary according to some authors. To our knowledge, no studies have focused on the effects of commercial thinning on wood mechanical properties according to tree social classes. The objective of this study is to verify, at the stem level, ( i) the effect of different commercial thinning intensities on the stem volume increment according to social classes (dominant, codominant, intermediate, and oppressed) and ( ii) the effect of commercial thinning on wood mechanical properties of white spruce ( Picea glauca (Moench) Voss), and ( iii) to determine if these effects on wood mechanical properties varied between social classes. The measurements were made from samples collected in a 32-year-old white spruce plantation that was thinned in 1989. We used stem analysis to measure volume increments, while the mechanical properties were measured on small pieces of wood (10 mm × 10 mm × 150 mm) without defects at dbh. Thinning has a significant positive effect on the stem volume increment for the dominant and codominant trees and no negative effect on the wood density, the modulus of elasticity and modulus of rupture for all thinning intensities and all social classes combined. After thinning (1989-2000), the modulus of elasticity increased by 50% in the dominant and by 70% in the codominant trees. This study allows us to consider the commercial thinning as a silvicultural tool to increase the productivity of white spruce plantations without affecting negatively the wood mechanical properties. Considering our results, we recommend that the intensity of the first commercial thinning should remove 35% of the basal area. [ABSTRACT FROM AUTHOR]