DISTRIBUTION

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

South-eastern Australian Distributions

Present and past climate is the main factor determining the distribution of Acacia vegetation, with soil type, topography and past fire regimes dictating the particular species distribution. In south-eastern Australia the major Acacia dominated communities occur on the western plains, and here microtopography is the major determinant of species distribution³¹ although soil factors also have an influence. In the east and south-east, on the slopes of the Dividing Range, the tablelands and the coastal areas, the dominance of the vegetation is predominantly by the eucalypts, although the Acacia species richness is greater than in the western region. Where dominance by an Acacia species occurs it is confined to only very local areas.

In the western regions, Mulga (A. aneura) favours the present semi-arid to arid climate in the northern half of western New South Wales. It forms extensive dense to open shrublands extending north from Hillston and west from Nyngan merging with the saltbush and bluebush shrublands further to the west. It occurs in the coarse-textured soils of sandplains and dune fields and the skeletal soils of the hills and low ranges. A number of other semi-arid trees and shrubs may be associated with the Mulga communities. Scattered outlier populations in wetter areas probably represent residual populations remaining from a past dry climate, presumably during the last glacial maximum about 17,000 years ago. To the north and north-west of Bourke in New South Wales, Gidgee (A. cambagei) is found as dense to open tall shrublands on a variety of soil types. Low woodlands and low open woodlands of Myall (A. pendula) are found on the fine-textured black-soil plains, extending from central Queensland into Victoria, to the east of the Mulga shrublands. Myall communities may be monospecific or associated with a number of other tree species. Brigalow (A. harpophylla) has its most extensive development in central Queensland and penetrates as far south as central western New South Wales, occurring mostly on heavy clay loams and is often associated with gilgai formations. Brigalow often forms dense monospecific communities. Ironwood (A. excelsa) woodlands are found in the northern part of New South Wales, mostly north and north-west from Nyngan on floodplains and sandplains; while Currawang (A. doratoxylon) is common on the skeletal sandy soils of hills and stony ridges further to the east of these other Acacia communities.

In the eastern and south-eastern region towards the coast where the rainfall is higher and droughts less severe and the topography and soils more varied, Acacia species may only be locally dominant or form a sub-canopy. For example, A. melaneoxylon may be dominant in localised closed forests in south-east Victoria and Tasmania. In the cooler-moist areas of New South Wales and Victoria, A. dealbata can form extensive sub-canopy associations while A. silvestris, and to a lesser extent, A. binervia may be dominant in localised dry tall shrublands³⁵ to the east of the Snowy Mountains in New South Wales. A number of species colonise particualr local habitats, such as A. filicifolia which often occurs along stream banks, and A. tindaleae may form tall heaths on sandy loams. Localised, fire-induced stands of Acacia species are also quite common.

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