A QUEENSLAND trial of two Corymbia hybrids could hold the key to major changes in sub-tropical plantation silviculture. The results could also help ease the transition from native forest logging on State-owned lands within 25 years (the Government and the forest industry reached agreement on this cut-off date in 1999) and development of a replacement sawlog resource based on plantations.
Dr Kevin Harding is leading a major silvicultural trial of Corymbia hybrids that has been planted at a site near Brigooda, north-west of Kingaroy, as part of Queensland Department of Primary Industries and Fisheries’ contribution to the CRC for Forestry Project 2.5, High-value wood products from sub-tropical plantations.
Dr Harding is a principal research scientist with Queensland DPI&F Innovative Forest Products section of Horticulture and Forestry Science. He leads a wood quality improvement research unit and has nearly 30 years experience focused on wood quality assessments of genetic and silvicultural trials and screening genotypes.
Corymbia hybrids (particularly the interspecific hybrids between C. torelliana and C. citriodora subspecies variegata) are among the most promising candidate taxa for eucalypt plantations in Queensland. They have performed well across a range of soil types in lower-rainfall climates where reasonably-priced land is available for future plantation development. They also display faster growth and better disease tolerance and frost tolerance than pure spotted gum (C. citriodora subspecies variegata).
The trial, covering over five hectares of experimental plots and buffers, tests several selected Corymbia hybrid families at two initial stockings (600, 800 stems per hectare). Thinning treatments (thinning to 200, 300 and 600 stems per hectare) and pruning treatments (nil, large branches only and to 5.4m) will be imposed as the stand develops.
“During the life of the CRC for Forestry, the trial will yield early results that will help growers optimise silviculture,” said Dr Harding.
He said that whether thinning carried out at early ages of three to four years could yield a useful commercial product would have an important bearing on plantation economics.
Study of the impacts of silviculture and genetics on growth and wood quality of the retained final-crop trees will be carried out over a longer time frame.
Conditions for planting were challenging for the DPI&F planting crew. Because of a prolonged dry period in the months leading up to planting, the site had to be pre-watered and seedlings watered in. Fortunately, substantial rain fell in the days immediately after planting.
Dr Harding is a wood quality specialist experienced with x-ray densitometry and non-destructive evaluation tools, and his recent research work is contributing to the development of wood quality models for exotic pine plantation decision support systems. Project design and implementation experience has included a variety of work in Australia, China and Vietnam. He has a Forestry degree from ANU (1978) and PhD from North Carolina State University (1995).
