Four years of girdling trials were carried out on Douglas-fir (Pseudotsuga menziesii) trees of grafted and seedling origin. Different girdling methods were applied, including complete removal of a band of bark and phloem, opposing partial bands, pruning-saw cuts, aluminum girdling inserts and a single knife-cut. Data were collected on seed and pollen cone production, tree vigour, girdle wound health and seed characteristics, for up to 4 years following girdling.
All treatments appear to be equally effective in promoting male and female flowering over ungirdled trees and, there were no differences among treatments in cone abortion, filled-seed percentages, or seed germination. However, treatments differed in their effects on tree vigour, seed weight and the speed with which the girdles healed. A simple knife-cut into the xylem seems to result in the least vigour loss and fastest healing, and is as effective as other treatments at increasing seed production. Recommendations are made for girdling procedures.
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Updated May 29, 2009