EFFECTS OF LONG-TERM PRUNING, MERISTEM ORIGIN, AND BRANCH ORDER ON THE ROOTING OF DOUGLAS-FIR STEM CUTTINGS

The rooting percentages of 14 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) clones were examined annually from 1974 to 1988. The trees were 10 and 13 years old in 1974 and were pruned to 2.0 m in 1978 and 1979 and then recut annually to 0.5, 1.0, or 1.5 m, starting in 1983. The pruned trees showed no evidence of decreased rooting percentage even after 15 years; average rooting increased from 47% in 1974 to 74% in 1986. Rooting percentage was significantly influenced by tree height. Cuttings collected from 0.5 m tall ramets exhibited better rooting than cuttings from 1.0 or 2.0 m tall ramets, and cuttings from 1.0 m tall ramets rooted better than cuttings from 2.0 m tali ramets. Rooting of cuttings collected from 0.5 m high subinterval zones within trees showed a negative linear relation between rooting percentage and collection height. Cuttings collected from the 0-0.5 m zone rooted 25% better than cuttings from the 1.5-2.0 m zone of the 2 m tall trees. That difference was significant at p < 0.05. A test of rooting of larger, more orthotropic cuttings gathered from the upper flat surface of pruned ramets indicated that the cuttings from the top rooted significantly less than smaller, more plagiotropic cuttings from the contiguous side areas (24 versus 33%, respectively). Rooting comparisons of meristems of primary and secondary origin showed significantly greater rooting of secondary meristems. Comparison of rooting of second-order and first-order meristems of secondary origin indicated the second-order twigs averaged 26% better rooting than the first-order branch tips when the cuttings were collected in January and placed in the rooting beds in February.