Mimosa pigra in Queensland.

The soil seedbank and growth rates of mimosa ( Mimosa pigra L. (Mimosaceae)) have been monitored at Peter Faust Dam, near Proserpine in central coastal Queensland, since early 2002. This infestation is the only known M. pigra infestation to have established in Australia outside of the Northern Territory. Originating from Central America, M. pigra poses a major threat to the integrity of northern Australia’s wetlands, reducing biodiversity and affecting primary production. In the Northern Territory, it has formed impenetrable nearly mono-specific thickets over 800 km, whilst in Queensland it is found over 80 hectares of land bordering the Proserpine water supply. This study on M. pigra’s biology has provided accurate and timely information that has assisted the efforts of the on-ground Queensland mimosa eradication program (which began in 2001). Studies on the soil seedbank have shown it to have declined by 90% from 2002 to 2005, with initial soil seedbanks measuring up to 19,000 seeds m at the Proserpine site. No seeds have been found below 10 cm of soil. Queensland M. pigra plants were found to flower as early as 67 days and pod at 155 days after emergence, compared to 180 days and approximately nine months, respectively, for Northern Territory plants. Flowering and podding in Queensland occurs all year round, whilst flowering in the Northern Territory occurs from February to May and podding from March to July, though flowering can occur whenever sufficient water is available. Information derived from the basic ecological studies at the Queensland site has assisted the timing of control activities (involving manual and chemical control), surveillance, extension and how long eradication should continue. The study has also shown that ecological studies can occur simultaneously within a control environment without compromising the objectives of eradication.