Effects of tree spacing on branch-size development during early growth of an experimental plantation of Eucalyptus pilularis in subtropical Australia

ABSTRACT Branch development in trees 1.6–5.7 years after planting was studied in a plantation experiment involving Eucalyptus pilularis in subtropical eastern Australia. The experiment compared stocking densities at planting in the range of 816–1667 stems ha−1 and rectangularities of tree spacing in the range of 1–6. Branch diameters at their bases were measured on the lowest 5 m of the stems of trees judged likely to yield sawn timber of high quality at final harvest. Neither stocking density nor rectangularity had substantial effects on branch numbers or diameters. Particular interest was paid to the presence of branches with diameters in excess of 2.5 cm that might produce knots large enough to degrade the quality of sawn timber. Such branches developed on lower stems between 2–4 years of age. An average of nearly five such branches was found on more widely spaced trees, reducing to 2–3 on more closely spaced trees. The results confirmed other work suggesting that pruning of high-quality eucalypt plantations should start near 2–3 years of age to both limit the development of large branches and restrict the size of knotty cores in logs. There was no evidence that changing the rectangularity of spacing to 3 or a little more, from the more normal practice of close to square, would affect such pruning regimes: increasing the distance between rows can reduce establishment and harvest costs and allow easier access for silvicultural operations.