This acacia has an extensive distribution in inland Queensland and extends into the central north of the Northern Territory. Its latitudinal range is 14-28o S at altitudes from 50-350 m. QLD, NT)
A nitrogen-fixing tree to 18 m tall and 40 cm diameter with rough longitudinally fissured dark grey bark. In close-spaced stands the crown is relatively narrow and the branches commonly ascend at an acute angle. Branchlets are angular, smooth and yellowish. The narrow phyllodes are grey-green, straight or slightly curved, 10-15 cm long by 2-7 mm wide. They have many fine parallel veins with the central vein usually more prominent. The flowers are in single or paired cylindrical spikes, 2-4 cm long. The pods are 4-6 mm wide and up to 12 cm long, somewhat woody, raised over and constricted between the seeds and finely wrinkled. The flowers appear in February - April and the seeds mature 6-7 months later. There are about 60 000 viable seeds per kilogram and pre-treatment with boiling water for one minute promotes germination.
Ecology/Way of Life:
The northern part of this species' distribution is in the hot semi-arid zone, but further south in Queensland the climate is warm semi-arid in inland areas and warm sub-humid nearer the coast. Most of the area is frost-free but there are occasional frosts in the south of its range. Mean annual rainfall is 500-750 mm with a well-developed summer maximum. It is found mainly on rocky outcrops and steep slopes of low sandstone hills and on dissected lateritic mesas. The soils are shallow, lateritic, red and yellow earths, sands or sandy loams and shallow podzolics. They are usually acid to very acid with low levels of nutrients and organic matter. Acacia shirleyi forms open-forests in the moister parts of its range and low woodlands or open-woodlands in drier areas. The communities are usually dense, pure stands of this acacia, sometimes with emergent eucalypts such as Eucalyptus trachyphloia, E. citriodora and E. drepanophylla. Most stands have no woody understorey.
Interaction with Humans/Threats:
The wood is hard, strong, heavy and relatively straight grained. It is often used for fencing material and makes excellent firewood. It has been used for specialised industrial purposes such as shuttles and spindles. This tree can provide shade and shelter on relatively harsh sites and is an attractive tree for amenity planting. It has had poor survival when planted as an exotic and this may because it is highly selective in its choice of Rhizobium strains for symbiotic nitrogen fixation. It is susceptible to termite damage.
Acacia shirleyi was named in 1920 by J.H. Maiden, former Government Botanist of New South Wales and Director of the Royal Botanic Gardens, Sydney. The name is formed from the Greek akakia = a thorny plant, specifically Acacia arabica; and honours J.F.Shirley (1849-1922), an inspector of schools in Queensland and a keen plant collector.
Brock, J. 2001. Native plants of northern Australia. Reed New Holland, Sydney. Doran, J.C. and Turnbull, J.W. (eds.) 1997. Australian trees and shrubs; species for land rehabilitation and farm planting in the tropics. ACIAR Monograph no. 24. Australian Centre for International Agricultural Research, Canberra. 384p.
Fitzgerald, P.J. 1991. The utilisation potential of Acacia shirleyi in the Northern Territory, Australia. In: Turnbull, J.W. (ed.) Advances in tropical acacia research, 151-152. ACIAR Proceedings no 35. Australian Centre for International Agricultural Research, Canberra.
Pedley, L. 1978. A revision of Acacia Mill. in Queensland. Austrobaileya 1: 75-234.
Topics:Soils Firewood Aboriginal resources Nitrogen-fixation Fodder Timber Germination
Text & map from Australian Trees and Shrubs, courtesy Australian Centre for International Agricultural Research; text edited by J. Turnbull; photo courtesy Maurice McDonald.
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