Effects of initial planting density and commercial thinning combined with pruning on black spruce wood quality and growth

An experiment was established in 1986 near Dégelis in Québec, Canada, to measure the effects of initial planting density and commercial thinning combined with pruning on the wood quality and growth of black spruce ( Picea mariana (Mill.) B.S.P.). A total of 8 levels of initial planting density ranging from 1111 stems/ha to 4444 stems/ha were compared. Except in control (unthinned) plots, commercial thinning from below was then carried out when basal area reached 28 m 2 /ha in each level of planting density. Analyses of variance were performed using generalized linear mixed models (GLMMs). Results show that black spruce wood quality was not affected by commercial thinning combined with pruning, but that it was closely linked to initial planting density. Growth variables were affected by both initial planting density and thinning scenario. Commercial thinning substantially reduced mortality rate, with thinned plots reaching a level 4.5 times lower than in unthinned plantations.