A risk assessment of the tropical weed Mimosa pigra in Northern Australia - Paper and presentation to the 3rd International Symposium on the Management of Mimosa Pigra, Darwin, September 22-28, 2002

Department of the Environment and Heritage, 2003

Internal Report 420
Walden D, van Dam R, Finlayson CM, Storrs M, Lowry J & Kriticos D
Supervising Scientist Division

About the report

Information on the biology and management of Mimosa pigra (mimosa) has been collated and analysed in a risk assessment in the regional context of northern Australia. Much of the information for this assessment has come from northern Australia where mimosa has been seen as a major weed for more than two decades, and has consequently attracted substantial research and management attention. The approach of this assessment adheres to the wetland risk assessment framework adopted under a formal resolution of the Ramsar Wetlands Convention. This framework provides guidance for environmental managers and researchers to collate and assess relevant information and to use this as a basis for management decisions that will not result in adverse change to the ecological character of the wetland. The risk assessment aims to determine:

  • What wetlands across northern Australia are at risk of mimosa invasion?
  • What are the likely consequences of mimosa invading these wetlands?
  • What management actions are being, or need to be undertaken to minimise the risks of further mimosa invasion across northern Australia?

The major wetland categories in northern Australia are briefly described and a summary of the effects of mimosa on native fauna, flora and socio-economic factors is presented. The current and potential distribution of mimosa in northern Australia is discussed along with factors influencing establishment, density and distribution, ie invasion rates and pathways, preferred habitats and environmental conditions and greenhouse considerations.

The prediction of the potential distribution compares annual rainfall zones with CLIMEX modelling, overlaid with potentially vulnerable wetlands and land tenure. These are discussed in the context of the current management of mimosa in northern Australia. Uncertainty and information gaps relating to the extent and effects of mimosa are also highlighted. An estimated 4.2-4.6 million ha of wetlands in northern Australia are under threat from mimosa, though the actual area of suitability within this range is unclear and dependent on further research. Resolving such uncertainty is seen as a priority task as it will provide a stronger basis for strategic research and control activities.