Pruning density is the relative number of trees pruned; pruning severity is the amount of live crown removed. Pruning density and severity experiments were installed in two coastal western hemlock (Tsuga heterophylla [Raf.] Sarg.) plantations, 12 and 13 years old, on Vancouver Island. The pruning density experiment indicated that a single 3-m pruning lift significantly reduced 4-year average diameter by 1.3 cm and height by 0.5 m, regardless of whether all or half the trees were pruned on a plot. Treatments in the pruning severity experiments reflected a range of residual crown lengths: 1.5, 2.5, 3.5, and 4.5 m, plus no pruning (control). After 4 years, there were obvious downward trends in both average diameter and height with increasing pruning severity. Significant growth reduction appeared below a threshold of about 50% retained crown ratio. The most severe pruning treatment (1.5 m) reduced 4-year average diameter by 4.3 cm and height by 1.5 m, compared with the control.
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Updated April 19, 2007