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Prickly acacia

Overview

Prickly acacia, originally from the Middle East, was introduced early in the 20th century for shade and fodder. During the early part of the 1900s, seeds were carried in saddlebags and distributed from horseback by graziers. The distribution of prickly acacia however did not become problematic until production in the area shifted from sheep to cattle. While sheep can digest the majority of the prickly acacia seeds they consume, cattle cannot and so act as major vectors.

Impact on environment

Prickly acacia converts grasslands to shrublands
Photo: Joel Brown

This small tree/shrub competes with native grasses, gradually converting productive grassland to unproductive shrubland. This is particularly important in the productive Mitchell Grasslands where the heaviest infestations of prickly acacia are estimated to cover more than 500,000 hectares.

Prickly acacia can produce more than 175,000 seeds per plant per year, and can rapidly displace native vegetation to form dense thickets. Wet years can generate a thousand-fold increase in plant numbers in some areas.

Management

Weed control programs so far have failed to contain the spread of this pest. In July 1999, a Prickly Acacia Containment Line was developed in central west Queensland an effort to help stop the spread of the weed. Inside the line are five 'islands' of core prickly acacia areas. These stretch from Barcaldine north to Hughenden and west to Winton and Julia Creek. Eradicating prickly acacia inside these areas is currently impractical or not economically feasible and efforts concentrate on researching biological control agents. Outside this line, the weed is eradicated with the support of Queensland Department of Natural Resources SWEEP program.

To see a recent list of research findings on prickly acacia click here.

Click here to read more about weeds in the Mitchell Grasslands.