The purpose of this research was to examine the effects of pruning and thinning on the growth and mortality of young Douglas-fir (Pseudotsuga menziesii [Mirb] Franco) stands on high-productivity sites in coastal British Columbia. To accomplish this, a two-way randomized incomplete block design with two blocks was established on a coastal site with three levels of thinning (no thinning, thin to 500 stems per ha, and thin to 250 stems per ha) and three levels of pruning (no pruning, prune 250 stems per ha, and prune all trees). The response variables of interest were diameter at breast height (dbh), height, basal area, total and merchantable volume, mortality, damage, and deformities. Dbh and height were examined both for all trees and for only the largest 250 sph by dbh trees (the crop trees). The dynamics in partially pruned stands were also examined. We found that only dbh, basal area, total and merchantable volume, and mortality were affected by thinning. Pruning did not have any effect on the response variables. The pruned trees in unthinned plots and the unpruned trees in thinned plots had a competitive advantage over unpruned trees in unthinned plots and pruned trees in thinned plots, respectively.
Significance: Applying a partial pruning silviculture treatment with the objective of reducing treatment costs by pruning only the minimum number of trees for full site utilization at the end of a rotation did not effectively target the crop trees 20 years after treatment in either thinned or unthinned stands.