DISTRIBUTION

Global | In Australia | The Acacia Community | South-eastern Australia | Diversity

Acacia communities

Acacia shrublands and low woodlands replace Eucalyptus communities in the drier regions of the Australia^29,30. Their distribution is influenced by the rainfall and temperature, and to a lesser degree by the soil type and soil pH. Most species are associated with free-draining, low fertility soils, although a few occur on richer soils and basalts, whilst some are associated with limy soils. While these factors determine the large scale vegetation groups, small scale structure and species distruibution, particularly in the arid and semi-arid regions, is influenced mostly by microtopography³¹.

In northern Australia, acacias are most extensive where the annual rainfall is less than 750 mm, and they replace eucalypts where the rainfall drops below 300 mm annually. Prior to widespread land clearance in southern Queensland, low open forests of Brigalow (A. harpophylla) covered extensive tracts of fine-textured alkaline soil country, forming almost pure stands. It extends to near the coast in central Queensland where the rainfall is less than 900 mm annually, and south into central New South Wales. Further inland, in lower rainfall areas, Gidgee (A. cambagei) replaces the Brigalow and also forms quite extensive stands, becoming lower and sparcer with decreasing rainfall. On the shallow coarse-textured acid

Fig. 6. Principal Acacia communities in SE Australia

soils associated with the residual mesas of the arid regions, A. shirleyi and A. catenulata dominate the associations²⁹ in south-west Queensland.

In the winter rainfall zone of southern Australia, Acacia are predominate where the annual rainfall is less than 250 mm³⁰. Myall (A. pendula) commonly forms reasonably extensive stands on the fine-textured soils in southern areas, although it does extend into central Queensland. Further west, through South Australia, it is replaced by A. papyrocarpa²⁹.

From western New South Wales and through the semi-arid and arid interior to Western Australia, Mulga (A. aneura) scrubs are the dominant vegetation type. They are common on the coarse-textured soils of the sandplains and dune fields. In the south of their range they are frequently associated with tussock grasses, while in the northern areas of their range the understory is usually hummock grasses ('spinifex')²⁹.

Global | In Australia | The Acacia Community | South-eastern Australia | Diversity