Southern Mahogany for Farm Forestry

Note Number: AG0893
Published: August 2003
Updated: September 2009

This Agriculture Note describes southern mahogany (Eucalyptus botryoides) as a farm forestry species.

Description

Eucalyptus botryoides is commonly known as southern mahogany, bangalay, swamp mahogany, or mahogany gum. It is closely related to Sydney blue gum (Eucalyptus saligna). Both species have discolorous leaves (dark green above, pale beneath) with distinctive fine veins at about 45° to the central vein. Mature southern mahogany is readily distinguished by its thick, rough, brown bark. It varies in form from a spreading heavily branched tree to a tall straight forest tree.

Southern mahogany naturally occurs in a narrow coastal belt of 700-1300 mm rainfall from Bairnsdale, Victoria to Newcastle, NSW (Figure 1), on a wide range of soil types from gravel and sand to fertile clay loam. Trees on sandy coastal soils are of a shrubby form, 8-12 m tall. Further inland on fertile loams in river valleys, southern mahogany is a tall forest tree reaching heights of 30 to 40 m.

Site requirements

Southern mahogany is suited to medium-high rainfall areas and is not drought tolerant. Minimum required annual rainfall is about 600 mm, but higher growth rates are achieved with more than 800 mm. It grows best on fertile clay loams with good drainage. However it is also suitable for coastal areas, due to tolerance of exposure, salt spray and poor soils. It has moderate tolerance of frost and waterlogging.

Wood properties

Southern mahogany has deep pink to red-brown heartwood and distinctly paler sapwood. The timber is strong with a medium texture and interlocking grain. Its density is about 1180 kg/m3 (green) and 930 kg/m3 (air-dried, 12% moisture). It has a CSIRO natural durability rating of 2-3 (moderately durable to durable) and expected life above and below ground of at least 15-25 years. The sapwood is seldom attacked by Lyctus borers.

The timber seasons readily, turns, machines and glues well, but can blunt knives and saws more quickly than some eucalypts. It is prone to severe growth stresses when young and should be quarter sawn to reduce damage.

Southern mahogany is slow to dry and is susceptible to end-splitting and some collapse. Air-drying in protected stacks can reduce such damage. Shrinkage is about 5% (radial) and 10% (tangential), or 4% and 7% after reconditioning.

Uses

Southern mahogany timber has been used in New Zealand for flooring, decking, veneering and furniture making. Other potential uses include general construction, poles and firewood.

Southern mahogany can also be planted for shade, shelter or windbreaks, (including in coastal areas), or for honey production. In open grown trees and windbreaks, heavy lower branches are retained. Southern mahogany can be direct seeded using 300-400 g/km or 1 kg/ha of viable seed.

Growth rates and provenances

Southern mahogany is a fast-growing species that should produce sawlogs in 30 years on suitable sites with appropriate pruning and thinning (see Agriculture Note AG0818: Growing trees for sawlog production). Its best growth and form occurs on fertile, higher rainfall sites at relatively low altitudes away from the coast, but it can outperform some species in the 600 to 700 mm rainfall zone, especially on sandier soils in coastal areas.

Seed sources

Little improved seed is yet available. Limited formal evaluation of natural provenances has been done and growth differences have generally not been significant. Growers using natural provenances should demand properly collected seed from superior trees in a good native stand. Collections should be based on at least 10 trees, all at least 100 m apart to ensure that they are not closely related. Seed from roadside or isolated trees is likely to be inferior.

Pests and diseases

Southern mahogany is susceptible to damage by leafblister sawfly, brown lace lerp, autumn gum moth, scale, leaf beetles and borers. However trees are generally resistant to attack when site selection and management are appropriate. Suppression through competition or drought stress makes trees more susceptible. Natural predators can help control small outbreaks. For more information, see Agriculture Notes AG0801: Insect pests – control and AG0799: Insect pests of young eucalypt plantations.

Further references

Bird PR (2000) Farm Forestry in Southern Australia: a focus on clearwood production of specialty timbers. Agriculture Victoria, Hamilton, Victoria

Bonney N (1997) Economic Native Trees and Shrubs for South Australias Greening Australia, South Australia.

Bootle KR (1983) Wood in Australia: types, properties and uses, McGraw-Hill Book Company, Sydney.

Brooker MI and Kleinig DA (1990) A field guide to eucalypts, vol. 1: south eastern Australia. Revised edition. Inkata Press, Melbourne.

Contact/Services available from DPI

See the DPI website (www.dpi.vic.gov.au), under “Forestry”, for more information including the Agriculture Notes series.

Customer Service Centre, telephone 136 186.

Acknowledgements

This note was developed by Rick Webb, Belinda Measki and Melanie Waters, August 2003.

It was reviewed by:

Tim Jackson Farm Services Victoria, November 2009.