Low-rainfall eucalypts as a potential plantation resource in south-eastern Australia for sawn appearance products

Summary

Four eucalypt species were evaluated for their potential to produce sawn appearance products when grown in the low rainfall (400–600 mm y¹) region of south-eastern Australia. The species were selected on the basis of their suitability for the region and the availability of sawlogs in existing plantations. The sampled trees were about 40 y-old with a minimum diameter at breast height over bark of 30 cm. A butt log 3.1 m long was harvested from ten or eleven trees of each of the following species: Eucalyptus astringens(Maiden) Maiden (brown mallet), E. cladocalyx F.Muell. (sugar gum), E. leucoxylon F.Muell. (yellow gum) and E. occidentalis Endl. (flat-topped yate). The logs were back-sawn with a conventional sawing system to produce boards mostly of 100 mm × 40 mm (nominal) cross-section.

The recovery of green boards that met high-value appearance grades was poor. The recovery of select grade or better boards ranged from only 0.9% of log volume for E. leucoxylon to 8.1 % for E. astringens. The poor recoveries were mostly attributable to the small diameter of logs and the lack of silvicultural treatment in the stands from which they were cut.

The results highlight the difficulties of growing high-value sawlogs in this region, without suitable silviculture. At best, given the expected long rotations, the economics of growing high-value sawlogs are likely to be marginal, and profitability will depend on other land management benefits provided by the trees. Improved genetic stock and appropriate silviculture will be critical if green recoveries (select grade and better) of at least 30–35% are to be achieved. Green recoveries of this magnitude are likely to be required for a viable sawn timber industry to be established in this region.

Use of a conservative air-drying schedule resulted in little drying degrade, surface checking being the main drying defect observed. Given the level of surface checking found, in the absence of other defects 85% of boards would still have made select grade or better. Nevertheless, careful drying practices will be required to minimise surface checking in back-sawn boards of each of these species.

Keywords:

• forest plantations
• sawnwood
• yields
• productivity
• dry conditions
• arid climate
• amelioration of forest sites
• Eucalyptus