Branch occlusion after pruning in four contrasting sub-tropical Eucalypt species

Branch related defects are the major cause of degrade in eucalypts grown for solid wood. The effects of pruning on the growth and branch occlusion in Eucalyptus cloeziana, E. pilularis, E. dunnii and E. grandis were studied. Trees of each species were pruned to remove 30% of the green crown at 3.5 years of age. Diameters and the state of all branches in two 0.5 m sections of trunk were assessed at one, two and four years after pruning. Growth rates were unaffected two years after pruning in all species. In all species, except E. cloeziana, the rate of occlusion of dead branches was not significantly different between pruned and unpruned branches. In contrast, the greatest difference in occlusion rates was between pruned and unpruned live branches. Eucalyptus grandis and E. dunnii showed high early rates of occlusion compared with E. pilularis and E. cloeziana for the first year. The occlusion rates of unpruned branches generally showed a positive correlation between branch size and time to occlusion. Relationships were more complex in species that self-pruned less efficiently. Since occlusion rates in dead branches (pruned and unpruned) were similar, there would be little benefit in pruning dead branches and it may increase susceptibility to decay entry and the occurrence of loose knots. Pruning only green branches may be difficult in efficient self-pruning species.