In 1991,a thinning and pruning experiment and pruning severity trial were installed in an 11-year-old coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) plantation near Chilliwack, B.C. The thinning and pruning experiment included three levels of thinning (no thinning, thin to 500 stems/ha, and thin to 250 stems/ha) and three levels of pruning (no pruning, prune 250 stems/ha, and prune all stems/ha) arranged in a 3 ×3 incomplete factorial. Eight-year data showed (1) that thinning and pruning effects were independent, and (2) that thinning had no effect on height growth, increased individual tree diameter and volume, but decreased per hectare total stand volume. Pruning to 3 m reduced height and diameter growth in the first 4 years following pruning, but pruned tree growth was equal to that of unpruned trees from 4 to 8 years. An unreplicated pruning severity trial at the same site examined four levels of crown retention (zero, one, two, four whorls remaining). Mortality exceeded 90% on the zero- and one-whorl treatments, and growth decreased with increasing pruning severity.
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Updated April 19, 2007