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Tasmanian blue gum

Image showing the tree Eucalyptus globulus.
Image showing the wood of Eucalyptus globulus.
Eucalyptus globulus

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.

Wood descriptionThis description can include heartwood and sapwood colour, grain, figure.

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.

Wood density

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.

Drying and shrinkageAs wood dries, it shrinks more in the tangential direction (i.e. parallel to the growth rings) than it does in the radial direction (i.e. at right angles to the growth rings). The figures given are shrinkage from green to 12 per cent moisture content, before steam reconditioning treatment, and with some species after stream reconditioning. Reconditioning is essential for recovering collapse which may have occurred during the drying process, and is essential for species such as the ash-type eucalypts of eastern Australia.

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.

WorkabilityWith south-west and plantation-grown trees, comments are made on the comparative ease or difficulty of turning, nailing and bending, on susceptibility to splitting and other working properties. With semi-arid, arid and desert species, a more complex survey was made and reported in Siemon and Kealley (1999). The properties assessed were turning, machinability, boring, screwholding, stability, sanding, gluing and finishing. A semi-quantitative score was used: very poor = 1, poor = 2, average = 3, good = 4, and excellent = 5. This book uses the descriptive terms rather than numbers.

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.

Durability

The CSIRO Durability Classes are based on the performance in ground of outer heartwood when exposed to fungal and termite attack.

ClassLife Years
1More than 25
215 to 25
38 to 15
4Less 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.

Strength group and properties

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

Strength Property S1 S2 S3 S4 S5 S6 S7
MOR 103 86 73 62 52 43 36
MOE 16300 14200 12400 10700 9100 7900 6900
MCS 52 43 36 31 26 22 18

Minimum values (Mpa) for green timber

Strength Property SD1 SD2 SD3 SD4 SD5 SD6 SD7 SD8
MOR 150 130 110 94 78 65 55 45
MOE 21500 18500 16000 14000 12500 10500 9100 7900
MCS 80 70 61 54 47 41 36 30

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.

Property Units Green Dry
Modulus of Rupture MPa 78 146
Modulus of Elasticity MPa 11000 20000
Max Crushing Strength MPa 40 83
Hardness KN 7.3 12
AvailabilityTimber from many species is available only in limited quantities, from near the areas where the trees grow naturally (or in plantations). There are other species such as red tingle and yellow tingle whose timber is rarely commercially available because the areas of occurrence are predominantly in conservation areas. Other species such as Goldfields timbers are only available in limited quantities because of their scattered occurrence and the fact that the industry is in the early stages of development.

There is slowly increasing availability from plantations in Western Australia, but most resource is managed for use as woodchips.

UsesVarious past and potential uses are given as a general guide, but the list is obviously not conclusive. In particular, there is increasing interest in specialty timbers, and the semi-arid, arid and desert area species have considerable potential for this use.

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.