Density and shrinkage of four low-rainfall plantation-grown eucalypts

Summary

Density and shrinkage values are presented for four eucalypt species (27-y-old Eucalyptus cladocalyx F.Muell. (sugar gum), 42-y-old E. occidentalis Endl. (swamp yate), 41-y-old E. astringens (Maiden) Maiden (brown mallet) and 40-y-old E. leucoxylon F. Muell. (yellow gum)) grown in low-rainfall plantations near Horsham in western Victoria. The mean basic densities for the four species were 752–827 kg m⁻³. The mean unit shrinkages were 0.37–0.41% for tangential shrinkage and 0.22–0.29% for radial shrinkage. These values are more or less comparable with those of wood sampled from mature trees of the same species.

Density and shrinkage values were also compared with published data for E. delegatensis R.Baker (alpine ash). The four low-rainfall species have much higher densities than E. delegatensis (511 kg m⁻³), but their unit shrinkages are only slightly higher than those for E. delegatensis (0.35% tangential and 0.22% radial) and should be manageable with appropriate design allowances.

Recoverable collapse, measured as the difference between shrinkage values (from green to 12% MC) before reconditioning (BR) and after reconditioning (AR), was evident in all four plantation-grown species (tangential, 2.4–4.1 %; radial, 0.4–1.3%). Despite this, steam reconditioning to recover collapse is not generally recommended because existing surface checks may reopen or become worse after steam reconditioning. In addition, the volume lost by not steaming is not large and ‘washboarding’ (localised earlywood collapse that results in a corrugated radial surface) does not occur with these species.

Keywords:

• wood properties
• wood density
• shrinkage
• dry conditions
• forest plantations
• eucalypts