By Dr Richard Seaton, Senior Ecologist and National Science Team member & Dr John Kanowski, Chief Science Officer
Australia supports over half a million species of plants, animals, fungi and other organisms. Reflecting our long isolation as an island continent, the great majority of these species are found nowhere else in the world. Nevertheless, in ancient times, a number of species successfully made the journey to Australia and established here. However, the pace of introductions from overseas stepped up dramatically with European colonisation, as a result of deliberate and inadvertent importation of exotic species to Australia.
An estimated 30,000 plant species have now been introduced to the country, of which some 10 per cent have become naturalised (i.e., established self-sustaining populations). Around 500 taxa (species and genera) have been declared noxious or are under some form of regulatory control because of their impacts on agriculture or the environment. Nearly all the 32 Weeds of National Significance (WoNS) – such as Gamba grass, lantana and rubber vine – have significant environmental impacts.
Many AWC properties are former cattle and sheep stations, which bear a legacy of weeds introduced during pastoral management. Even the most remote and pristine country managed by AWC is at risk of weed invasion as weeds can be transported long distances by wind, water, animals and human activity. For these reasons, weed management is a routine part of AWC’s conservation work.
Recently, AWC has developed a National Weed Management Strategy to help focus our weed control efforts on weeds having the greatest impact on our mission. National Strategies are a tool for integrating science and land management and for finding the best solution to the problem at hand. On a national scale, prioritisation of weed species is necessary because not all weeds can be eradicated from all AWC properties, and we want to direct our efforts to controlling weeds that have the greatest detrimental impacts on conservation values. Further, weed management uses resources that could be directed to other threat management and conservation activities, such as feral animal control; so, it’s important to allocate resources to the highest priority threats.
The specific objectives of AWC’s National Weed Strategy are that:
• Weeds with major impacts on ecosystems of high conservation value are prioritised for control on AWC properties;
• Allocation of resources to weed control within and between AWC properties is optimised, based on impacts of weeds on conservation values, and the feasibility of control; and
• New weeds with major environmental impacts do not become established on AWC properties.
Lantana (Lantana camara) is a thicket-forming, fast-growing scratchy shrub introduced to Australia from South America as a garden plant with pretty flowers. Its fruits are dispersed by birds, and in the absence of regular fire, lantana can form dense, impenetrable thickets in the understorey of eucalypt forests and in disturbed parts of rainforest. These thickets prevent regular, cool fires but also support intense wildfires that carry fire into the canopy of sensitive vegetation. They also degrade important habitat, suffocating plants like Pararistolochia praevenosa, an Australian vine on which the threatened Richmond Birdwing Butterfly (Ornithoptera richmondia) depends for survival.
On Curramore, in the areas of lantana infestation targeted by AWC’s land managers and volunteers, using a combination of manual removal and herbicide, around 31 hectares are in advanced stages of recovery and treatment is in progress on 18 hectares (see map). This has resulted in the mass recruitment of native trees, shrubs and vines, restoring the ecosystem to its natural condition. Curramore now stands out as a showcase for lantana control in the region and highlights the effectiveness of AWC’s weed management strategy.
Mount Zero–Taravale is a much larger property than Curramore and, at acquisition, around 2,400 hectares of the property were infested with lantana. Here, infestations of lantana have been reduced by at least 50 per cent by deliberate use of targeted hot fire in areas protected by surrounding early season burns and complemented by strategic use of herbicide to open up some of the denser patches.
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