The noxious weed, Rubber Bush Calotropis procera (Aiton) W. T. Aiton (Asclepiadaceae) is thought to have been introduced into Australia in the early 1900’s, was naturalized in Queensland by 1935 and reported in Mataranka, Northern Territory around 1946-7. It currently occurs in Queensland, the Northern Territory, Western Australia and northern South Australia and is spreading. Rubber Bush is a shrub that grows to a height of 1.7 - 6 m, can establish at high densities of 7 plants m-2 and favours shrubby rangelands and grasslands, where it hinders pastoral management.
From 2008 to 2011, it was estimated that 69% of beef cattle sales from northern Australia came from broad acre farms comprising 1600 cattle stations in which native grassland was the predominant feed resource. These grasslands are vulnerable to invasion by Rubber Bush and the species has already invaded large parts of the Barkly Tablelands and the Victoria River District (VRD). Landholders spend on average $7625 each on Rubber Bush control annually and pastoral companies in Australia consider Rubber Bush a serious problem and devote considerable amounts of money to its management. A number of knowledge gaps in the ecology and biology of Calotropis procera were identified which hampered efforts to control its spread.
The broad aim of this research is to assess the invasive potential of Rubber Bush, specific objectives being to investigate:
i) the competitiveness of Rubber Bush in native grassland;
ii) the dispersal processes and syndrome involved in its spread;
iii) the reproductive biology and recruitment rates of Rubber Bush;
iv) the population ecology of the species in northern Australia; and
v) use all this information to model rate of spread and potential future distribution of Rubber Bush.
The work involves conducting field experiments within plots in exclosures, observational studies, sampling and laboratory experiments.