Environmental Weed risk assessment in the Wet Tropics: addressing problems of invasive alien species as a major threat to landscape integrity and health

The issue of alien plant species invasions of the Wet Tropics bioregion was examined, and the implications for World Heritage management considered. The paper presents a brief review of Risk Assessment Systems (RASs) currently applied or being developed, with a view to formulating a robust system to screen alien species that have naturalised within the bioregion. The rationale behind the proposed Wet Tropics environmental weed RAS, which was derived from existing systems, is considered prior to its application as a screening tool. A list was compiled comprising 508 taxa of exotic (alien) plants that have established self-maintaining populations within the Wet Tropics bioregion. The paper reports on a preliminary ranking, employing the proposed RAS, of 7 aquatic and 50 terrestrial weed species. The six highest ranked species included Annona glabra (a weed of national significance or WONS) and the introduced forage legume Leucaena leucacepha/a; followed by the highly invasive Cliromolaena odorata (a very high priority declared plant); Miconia calvescens (similarly classified); Hymenachne amplexicau/is (a ponded pasture species now classified as a WONS); and Sphagneticola trilobata (a ground-cover species formerly used as- a _bank stabiliser but under consideration for declaration as a plant requiring control in environmentally sensitive areas under new State legislation). Consideration was also given to weed management issues, particularly with respect to some of the worst environmental weeds, and recommendations for further research are presented