“Boxed-Heart” Posts From Small-Diameter Durable-Eucalypt Plantation Thinnings PRB357-1415
This project assessed the suitability of young (9-16 year-old) hardwood logs for the production of boxed-heart posts from four species being Eucalyptus botryoides (southern mahogany), E. cladocalyx (sugar gum), E. muelleriana (yellow stringybark) and Corymbia maculata (spotted gum) – all durability class 1 and 2 above ground. The primary potential benefit being to increase income from thinning operations, which would otherwise only be suitable for low-grade pulpwood or firewood markets.
This project sought to identify key log attributes, silviculture treatments, harvesting techniques and drying methods to improve post quality.
Logs were sourced from commercially managed plantations that were age 9.5 and 11.5 years at the time of thinning. Records of Dbh, competition index (CI) and pruning were taken for each tree prior to harvesting. A target of approximately 80 posts was sought from each species.
Four drying treatments were employed across each of the four species. These included three Green-sawn treatments and one Dried Round (under water) treatment. Two of the green sawn treatments were air dried and one received a combination of air and kiln drying. Gang plates and End-wax sealer treatment was used in combination with the air dried treatments.
Posts were assessed after approximately 12 months of drying for both moisture content and checking (splits) of post surfaces and ends. The widest split on the ends and faces of each post was recorded. Splits in excess of 5 mm on any face or end rendered posts unacceptable.
The results suggest the potential for producing viable numbers of posts from small-diameter eucalypt-plantation thinnings, in particular from spotted gum and yellow stringybark. The best outcome across all of the treatments and species was found to be a 50% recovery of acceptable posts from spotted gum when green sawn, End Waxed and Plated (EWP).
The largest impact on post acceptability was checking in excess of 5mm on at least one face. Anecdotally this was most common on the face exposing the largest amount of inner heartwood.