Abstract
At age 5–6 years, rooted cuttings in a western hemlock (Tsuga heterophylla) clonal seed orchard received either a severe (ST) or moderate (MT) top pruning (upper 50 and 25% of live crown removed, respectively), or were left untopped (UT). Over the following 6 years, UT trees increased in height from 1.5 to 3.9 m, whereas through annual and biennial top and side pruning, MT trees grew to 2.2 m and ST trees were maintained at 2.0 m. Crown pruning had no effect on the subsequent annual production of seed or pollen cones. Spray applications of gibberellin A4/7 in years 2 and 4 of the study increased 5-fold and 2-fold the percentage of trees producing a medium and greater crop, respectively, of seed and pollen cones in each year 3 and 5.
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