Sydney Blue Gum for Farm Forestry

Updated: January 2008

AG0848

Philippa Noble, Wangaratta

This Agriculture Note describes the characteristics, site requirements and wood quality of Sydney blue gum (Eucalyptus saligna) as a farm forestry species.

Figure 1. Sydney blue gum plantation

Figure 2. Thinning of Sydney blue gum plantation

Sydney blue gum (Figure 1) is a well-known Australian timber tree. It is an excellent candidate for farm forestry and is increasing in popularity as a plantation species. This is due to its characteristics of good form, self-pruning and early wood maturity, its ability to grow in a wide range of soils and the suitability of the timber for a wide range of uses.

The name Sydney blue gum refers to its natural occurrence in the Sydney area, and to the sometimes-bluish appearance of the smooth bark. The species is not closely related to the blue gums of Victoria or Tasmania.

Natural occurrence

Sydney blue gum naturally occurs in tall open coastal forests, northward from around Bateman’s Bay to southern Queensland, mostly on deeper, moist soils in valleys or on sheltered lower slopes. In northern localities it extends up to the high slopes and ridges. It is usually found within 160 km of the coast, from sea level up to 300 m in the south and 1200 m elevation in the north.

Provenances

Sydney blue gum is closely related to southern mahogany (E. botryoides) and flooded or rose gum (E. grandis). It has a similar appearance to E. grandis, making identification difficult. There has been little provenance selection although some variation in stem form, growth and resistance to frost seems to exist. A provenance from Kangaroo Valley in the Nowra area has been reported as having reduced end-splitting. So far, trials of 9 year old trees in Western Victoria have shown minimal significant differences between the provenances with the best performer being a provenance from Clyde R, Yadboro, and 3 year old trials in southern NSW have shown the provenances from Camden Park, Koorlong and Paddys Landing are showing superior growth. Improved seed from stands in WA are available, with seed orchard seed soon to be available in NSW and Victoria.

Site requirements

Sydney blue gum prefers sites with an average rainfall of 850 -1600 mm, with a minimum of 760 mm. The species has fairly shallow surface roots so it does not tolerate dry sites. It can tolerate light frosts, but the absolute minimum temperature is -8oC. While naturally occurring in a summer rainfall zone, it has been grown successfully in areas where there is a winter rainfall maximum and in irrigation areas. Best growth is on good quality alluvial flats, with other preferred soil types being sandy loams, podsols and volcanic loams. It does not like very heavy clay soils, having only a little tolerance of poor drainage. It is sensitive to exposure and crown and branch breakage can occur in strong winds.

Growth rates

Sydney blue gum is a fast growing tree which can reach a height of 30-55 m and 2 m in diameter in its natural habitat. Growth rates of around 24 m3/ha/yr have been reported in Australia. In Brazil, growth rates of 35 m3/ha/yr have been recorded and in New Zealand, growth rates comparable to Radiata pine were observed ie. diameters of 58-62 cm at breast height in 20 years. On fertile loams with a high rainfall, growth rates are similar to E. grandis. In New Zealand, initial high growth rates were followed by declining growth rates, irrespective of site or stocking density. This has resulted in the species becoming less popular in that country than in the past

Management

The species has generally good form, with a long, straight bole. It sheds its branches evenly and cleanly for half to two thirds of its total height, but occasionally large branches remain which need pruning to ensure knot defects do not downgrade the timber. Wider spaced plantation grown trees will usually need pruning as heavy branches commonly develop in these circumstances.

The shallow root system makes weed control in the establishment phase a high priority for maximum growth.

The species coppices vigorously and a second crop can be grown. The advantages of coppicing need to be weighted against the cost of protecting stumps from damage during harvesting and the lack of potential to use improved seedlots or provenances.

Pest and disease risks

Sydney blue gum is susceptible to attack from a number of insect pests. Leafblister sawfly, christmas beetles, lerps, and leaf hoppers can infest trees at any age. Autumn gum moth and grasshopper outbreaks can occur in young trees with juvenile foliage. Borer attack can occur where trees are weakened due to disease or pest attack or by being grown on poor quality sites.

Uses

The timber from Sydney blue gum is one of the more important general construction timbers in New South Wales. It is also used for cladding, flooring, panelling, and boat building. It has potential as a furniture timber, as well as for export sawlogs and poles. The pulpwood produced from this species is acceptable but not preferred because of its low pulp yield and low paper tensile strength

Wood quality

Figure 3. Wood grain

The wood is dark pink to red brown in the heartwood with a paler, easily distinguishable sapwood. The grain is straight or slightly interlocked, and gum veins are common. It is moderately durable, with garden sleepers lasting 8 – 15 years. It is easy to work, dress and finish and takes a good polish. Mature wood characteristics develop at an early age. The green density is about 1070 kg/m3 and the air-dry density at 12 % moisture content is about 850 kg/m3. Rapidly grown plantation timber can have densities as low as 450 – 600 kg/m3.

High levels of growth stresses in Sydney blue gum logs can have a significant impact on yield, frequently causing brittleheart near the centre of the stem, with log splitting and distortion of the timber during sawing. Unfortunately, it is difficult to detect brittleheart, which means it is difficult to grade material for structural uses. Low recoveries from sawing are likely if logs of less than 30 cm small end diameter are used.

Drying characteristics

Sydney blue gum is easy to dry, relative to most other eucalypts, with moderate shrinkage. Collapse is slight but the heart centre material is inclined to split quite severely, so it is not recommended for large girders. Air drying to moisture content of 25% is a normal practice. Reconditioning is recommended during the kiln-drying process.

Summary

Sydney blue gum is an excellent farm forestry species. It grows on a variety of soil types, and is well suited to irrigation. It grows with a good straight trunk which needs minimal pruning to produce clearwood, and the timber is easy to dry and useful for a wide range of products.

References

• Bootle, K.R. (2004). Wood in Australia. Types, properties and uses. McGraw-Hill Book Co, Sydney.
• Borschman, R., (May 1996). Report on the Monitoring and Evaluation of Farm Forestry Sites in North East Victoria. North East Farm Forestry Program, Centre for Forest Tree Technology.
• Costermans, L., (1994). Native Trees and Shrubs of South Eastern Australia. Lansdowne Publishing Pty Ltd, Sydney.
• Hall, N., Johnston, R.D., and Chippendale, G.M. (1975). Forest Trees of Australia, Australian Department of Agriculture, Forestry and Timber Bureau, Australian Government Publishing Service, Canberra.
• Hillis, W.E. & Brown, A.G., Ed. (1984). Eucalypts for Wood Production , CSIRO Australia.
• Northway R.L (1996). Evaluation of Drying Methods for Plantation-Grown Eucalypt Timber: (a) Kiln drying trials with four species. CSIRO Forestry and Forest Products Report. Australia.