Mulga is highly variable, in form, in height, and in shape of phyllodes and seed pods. It can form dense forest up to 15 metres high, or small, almost heath-like low shrubs spread well apart. Most commonly, it is a tall shrub. Because it is so variable, the taxonomy of the Mulga has been studied extensively, and although it is likely to be split into several species eventually, there is as yet no consensus on how or even if this should be done. Although generally small in size, Mulga is long-lived, a typical lifespan for a tree undisturbed by fire is in the order of 200 to 300 years.
Mulga has developed extensive adaptations to the Australian desert. Like many Acacia species, Mulga has thick-skinned phyllodes. These are optimised for low water loss, with a high oil content, sunken stomata, and a profusion of tiny hairs to reduce transpiration. During dry periods, a Mulga drops much of its foliage to the ground, which provides an extra layer of mulch and from where the nutrients can be recycled.
Like most Australian Acacia species, mulga is thornless. The needle-like phyllodes stand erect to avoid as much of the midday sun as possible and capture the cooler morning and evening light. Any rain that falls is channeled down the phyllodes and branches to be collected in the soil immediately next to the trunk, providing the tree with a more than threefold increase in effective rainfall. Mulga roots penetrate far into the soil to find deep moisture. The roots also harbour bacteria that fix atmospheric nitrogen and thus help deal with the very old, nutrient poor soils the species grows in.
Mulga savanna and mulga co-dominant 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 Acacia 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 that it grows in 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. The dominant species in these woodlands is Mulga with poplar box (Eucalyptus populnea) forming an increasingly important co-dominant in the eastern districts. The extent of ground cover in mulga woodlands varies with canopy density of the overstorey, becoming almost non-existent 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 itself, 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 may require the stimulus of fire to scarify and promote germination. Long-lived seed store in soil is also common in these woodlands.
There are a number of recognised varieties:
The seeds of Acacia aneura were used to make seedcakes. The mulga apple is an insect gall commonly eaten by Aborignal people. Mulga tree gum (Ngkwarle alkerampwe in the Arrernte language) is a type of lerp scale found on mulga branches. It provides a tasty honey-like treat for Indigneous people.
Wood from Acacia aneura stands up very well to being buried in soil and it is used for posts. The wood has a density of about 850-1100 kg/m3.
Total soil organic matter and its labile pools following mulga (Acacia aneura) clearing for pasture development and cropping 1. Total and labile carbon.
Jan 01, 2005; Introduction Communities dominated by mulga (Acacia aneura F. Muell. Ex. Benthan N-fixing tree legume) occur extensively in...
Total soil organic matter and its labile pools following mulga (Acacia aneura) clearing for pasture development and cropping. 2. Total and labile nitrogen.
Mar 01, 2005; Introduction About 150Mha of Australia originally supported mulgadominated (Acacia aneura F. Muell. Ex. Benth.) woodlands...