Effects of annual crown pruning and serial propagation on rooting of stem cuttings from Douglas-fir

Abstract

Success of rooting from stem cuttings of 14 Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) clones increased significantly from 42% in 1974 to 67% in 1981. The increase was slightly more than 3% each year despite ortet age increasing from 10 and 13 years in 1974 to 17 and 20 years in 1981. The greatest increase occurred from the 3rd through the 6th year of annual rooting trials. Yearly pruning of ortets and rooted ramets of the same clones is thought to have reinvigorated shoots from the pruned crowns of trees. Several annual prunings seemed to be required before average rooting potential increased markedly. No translocation of the reinvigoration stimulus from the pruned to the adjacent unpruned areas of the same trees was detected. Rooting of cuttings from ortets from pruned areas was at least 9% more than cuttings from unpruned areas. No additional invigoration from serial propagation of cuttings was noted for rooting potential, but such cuttings grew a little taller and slightly less plagiotropic 1 year after rooting than were ramets propagated from pruned ortets. Significant clonal variation was found with all treatments. Evidence of a change in physiological vigor of the ortets and rooted ramets was externally visible in the formation of abundant lammas shoots on pruned areas of the 17- and 20-year-old ortets and rooted ramets. Abundant lammas growth is normally found only on Douglas-fir trees less than 10 years old.