Tasmanian blue gum is referred to as 'Western blue gum' when genetically-improved material is used for plantations in the State. The Standard Trade Name is 'Southern blue gum'. In the native forest, blue gum varies from a medium-sized woodland tree 15-20 m in height with branches retained to below one-third of total height, to an impressive forest tree of excellent form, to 70 m in height and 2 m diameter. On very harsh, exposed sites such as Flinders and King Islands it may be reduced to a mallee-like shrub. Occurs naturally in south-east Tasmania, the Bass Strait Islands and south-east Victoria. Its low level of frost tolerance restricts distribution to low altitudes and near coastal locations. Extensive plantations have been established in the south-west of Western Australia on ex-pastured land.
Heartwood is a light yellowish brown, sometimes with a pinkish tinge. Sapwood is paler, not always distinguishable from heartwood, and up to 50 mm wide. The texture is medium and grain often interlocked, and growth rings are distinct, particularly on end grain.
Green density is the density of wood in the living tree, defined as green mass divided by green volume, and useful for estimating transport costs. It varies with season and growing conditions.
Air-dry density is the average mass divided by volume at 12 per cent moisture content (this is the average environmental condition in the coastal capital cities around Australia).
Basic density is oven-dry mass divided by green volume. This measure has the advantage that moisture content variations in the tree during the year are avoided.:
Green density of young Western Australian-grown timber is about 1040 kg/m3, air-dry density about 740 kg/m3, and basic density about 540 kg/m3.
Tangential and radial shrinkage of 17-23-year-old material before reconditioning are about 14.5 and 7.0 per cent respectively, and after reconditioning about 9.5 and 4.6 per cent respectively.
With workability, the timber needs care in drying to minimise checking of the tangential surface. Quartersawing (at right angles to the growth rings) is recommended because of surface checking. Considerable collapse can occur, but this can be recovered by steam reconditioning.
The CSIRO Durability Classes are based on the performance in ground of outer heartwood when exposed to fungal and termite attack.
|1||More than 25|
|2||15 to 25|
|3||8 to 15|
|4||Less than 8|
The ratings are not relevant to above-ground use. In late 1996, CSIRO published revised ratings, which include termite susceptibility. Ratings are now available for about seventy species for decay, and for decay plus termites.:
The Durability Class based on the 1996 CSIRO assessment is 3 for decay, and 4 for decay + termites combined. Sapwood is Lyctus-susceptible.
Minimum values (MPa) for strength groups for green and seasoned timber come from Australian Standard AS2878-1986 'Timber - Classification of strength groups'. In grading structural timber, each species is allocated a ranking for green timber of S1 (strongest) to S7, and for seasoned timber SD1 (strongest) to SD8.
MOR is modulus of rupture or bending strength, MOE is modulus of elasticity or 'stiffness', and MCS is maximum crushing strength or compression strength. Hardness refers to the Janka hardness test and is a measure of resistance to indentation.
Minimum values (Mpa) for green timber
Minimum values (Mpa) for green timber
Where test data were available, they are shown in bold print. Most values are from Bootle (1983), Wood in Australia. Types, properties and uses. (McGraw-Hill), or Julius (1906), 'Western Australian timber tests 1906: The physical characteristics of the woods of Western Australia'.
Where no strength data were available, air-dry density was used in accordance with the Australian Standard AS2878-1986 Timber - Classification of strength groups to predict the strength group. Consequently, the strength values quoted are from the above two tables.:
Green and dry strength groups for timber from mature trees are S3 and SD2 respectively. There are no data for plantation-grown trees, but the more important strength properties for mature wood are given in the table below.
|Modulus of Rupture||MPa||78||146|
|Modulus of Elasticity||MPa||11000||20000|
|Max Crushing Strength||MPa||40||83|
There is slowly increasing availability from plantations in Western Australia, but most resource is managed for use as woodchips.
The uses are mainly for pulp and paper, rayon, general structural timber, flooring and furniture timber. If preservative-treated, round timber can be used for posts, poles, sleepers and fence posts.