Effect of cutting diameter and stem or branch position on establishment of a difficult-to-root clone of a Populusalba hybrid

A total of 357 hardwood cuttings 20 cm long were collected from 22 one- and two-year-old trees (established from rooted cuttings) of a difficult-to-root Populusalba × P. grandidentata clone. The cuttings, planted in book planters, were grown in a greenhouse for 3 months; survivors were then transplanted into the field. Survival and growth were recorded periodically. After 2 months in the greenhouse, height growth was significantly related to diameter, but there was no further diameter effect on height growth after that. Branches, 1- and 2-year-old stem wood provided cuttings with comparable survival percentages for any given diameter class. Survival increased with increasing cutting diameter of both stem and branches and was highest for cuttings from the lower positions of the stem and branches. Position was slightly more efficient than diameter as a selection criterion of stem cuttings, since cuttings from the lower stem positions generally had high survival even if diameters were relatively small. However, for branch cuttings, selection based on diameter alone adequately segregated those with the best survival. Of several proposed alternative cutting selection criteria, two were judged to be best. They were to select (1) all cuttings with diameter > 9 mm and (2) a combination of all branch cuttings with diameter > 9 mm plus the four basal stem cuttings regardless of diameter. When these selection criteria were used survival increased from 29% to just over 50%.