A form diagram to optimise pruning schedules for eucalypt clear-wood production

SummaryBranch pruning is necessary to produce high-value wood products from eucalypt plantations. Four requirements of an effective and efficient pruning regime for clear-wood production are to (a) restrict the pruned-stem diameter to a specified maximum, (b) ensure only green branches are pruned, (c) remove a proportion of the green crown that allows for continued competitiveness of the pruned trees and (d) minimise the number of pruning interventions. In this paper, we present a pruning decision support tool that diagrammatically combines results from growing stands and crown reduction trials. Elements depicting the pruning schedule, target maximum pruned diameter (PDmax), lower height of the green crown (GCLH) and target retained proportion of the green crown (GCRP) are overlaid onto a set of stem-taper curves. The form diagram was demonstrated using data from two adjacent commercial plantations of Eucalyptus pellita (Caravan Hill and Fishtail), established in the same planting season, for solid-wood production in northern Queensland, Australia. We fitted a cubic tree taper model that described 89% of the variation in stem diameter at a given height. PDmax was set at 12 cm and GCRP was set at 50%. Pruned height was set at 6 m assuming two lifts.Site differences in E. pellita growth, slenderness and green-crown height resulted in different optimum pruning schedules even on adjacent holdings. Within-stand heterogeneity in slenderness and green-crown height contributed further to the complexity of pruning scheduling. Our results suggest that it would have been necessary to complete the Fishtail site pruning program at the commencement of the second dry season after planting to ensure that the pruned height was always greater than GCLH. On the other hand, the first pruning lift could be conducted at the Caravan Hill site at the same time that the second lift was being completed at Fishtail. Management options that increase the height growth in the first year, promote live crown retention and increase within-stand homogeneity will improve the effectiveness of fixed-lift pruning for eucalypt clear-wood production. © 2013 Institute of Foresters of Australia (IFA).