Effect of Top Pruning, Branch Thinning and Gibberellin A4/7 Treatment on the Production and Distribution of Conebuds in Douglas-fir

1989

S. 177-185

4 Abb., 3 Tab., 26 Lit. Ang.

Unselbständiges Werk

200051093

Three levels each of top pruning and branch thinning (in February), with and without stem injections of GA4/7 (during June and July), where replicated in two blocks of a 7-year-old Douglas-fir (Pseudotsuga menziesii) seedling seed orchard. Flowering was assessed the following year and height extension over two years when the study was accidently terminated by management activities. In one orchard block, topping trees from six whorls of branches to five or three whorls depressed female and male flowering disproportionately relative to contributions of the removed crown regions in untopped trees. Trees in the other block were less vigorous and fecund. Here the light top pruning also depressed female and male flowering but only in proportion to its severity. Heavy pruning increased the tree production of seed cones relative to untopped trees and had no effect on male flowering. Thinning of interwhorl and (or) smaller whorl branches depressed female flowering in approximate proportion to the branches' contribution in unthinned trees, but had a disproportionate effect on pollen-cone production. Results are discussed in relation to the hypothesis that flowering response to top pruning and branch thinning is a function of the vegetative vigor response of shoots following release from apical control. Treatment with GA4/7 increased the production of seed- and pollen-cone buds by 161% and 91%, respectively, although seed-cone abortion was also 35% higher in GA4/7- treated trees. A modified stem- injection method for the operational GA4/7 treatment of Douglas-fir seed orchards is discussed.