Acacia Aneura - Habitat and Ecology

Habitat and Ecology

Mulga savanna and mulga codominant tussock grasslands cover roughly 20% of the Australian continent, or about 1.5 million square kilometres. The mean rainfall for much of the habitat for A. aneura in Australia is roughly 200–250 mm/year, but it goes to as high as 500 mm/year in New South Wales and Queensland. The lowest mean rainfall where it grows is about 50–60 mm/year. Both summer and winter rainfall are necessary to maintain mulga, and the species is absent from semiarid regions that experience summer or winter drought.

Mulga scrub is distinctive and widespread, with the Mulga Lands of eastern Australia defined as a specific bioregion. The dominant species in these woodlands is mulga, with poplar box (Eucalyptus populnea) forming an increasingly important codominant in the eastern districts. The extent of ground cover in mulga woodlands varies with canopy density of the overstorey, becoming almost nonexistent in extremely dense stands. In more open stands, the herbaceous layer consists of wire grasses (Aristida spp.), mulga oats (Monocather sp.), mulga mitchell (Thyridolepis sp.), wanderrie (Eriachne spp.), finger grasses (Digitaria spp.) and love grasses (Eragrostis spp.). Various other woody species are also significant in mulga woodlands, particularly hop bushes (Dodonaea spp.), Eremophila and cassia (Senna spp.).

In contrast to the eucalypt woodlands that dominate much of Australia, mulga woodlands are not well adapted to regular fire and species in mulga communities vary in their ability to survive fires. Many species, including mulga, have a very limited ability to resprout after fire, and rely instead on mechanisms of seed production for species survival. Many plants produce hard, woody fruits or seeds, which can not only survive intense heat, but also may require the stimulus of fire to scarify and promote germination. Long-lived seed stores in soil is also common in these woodlands.

The recognised varieties are:

• A. a. var. aneura
• A. a. var. argentea
• A. a. var. fuliginea
• A. a. var. intermedia
• A. a. var. macrocarpa
• A. a. var. major
• A. a. var. microcarpa
• A. a. var. pilbarana
• A. a. var. tenuis