A weed is any plant that requires some form of action to reduce its effect on the economy, the environment, human health and amenity. Weeds are also known as invasive plants. Many plants introduced into Australia in the last 200 years are now weeds.
Weeds typically produce large numbers of seeds, assisting their spread. They are often excellent at surviving and reproducing in disturbed environments and are commonly the first species to colonise and dominate in these conditions.
A weed can be an exotic species or a native species that colonises and persists in an ecosystem in which it did not previously exist. Weeds can inhabit all environments; from our towns and cities through to our oceans, deserts and alpine areas.
Some weeds are of particular concern and, as a result, have been listed for priority management or in legislation.
Throughout Australia, weeds are spreading faster than they can be controlled and management of them is consuming an enormous amount of resources. Climate change poses an additional challenge to our ability to manage weeds.
A range of management frameworks has been developed to help coordinate the management of weeds at different levels of government throughout Australia.
Native plants as weeds
Not all of Australia's weeds have come from other countries. Australian native plants can also become weeds when given the opportunity. This usually occurs when species move from within their natural habitat into new areas where they have a competitive advantage over indigenous plants, allowing them to establish naturalised populations. Native plants can also become weeds when characteristics within their natural habitat change, enabling them to better compete with other species and increase their population size and/or density.
All Australian states and territories have experienced native plant invasions. For example, in Victoria around 200 species have naturalised outside their native range. A common example of a native plant establishing itself outside its natural range is the Cootamundra Wattle Acacia baileyana.