Weeds – the real alien invaders
Box 2 | How to be a good weed
Successful weeds have certain traits that allow them to become a threat in their new environment. A common trait is the ability to produce large numbers of seeds, allowing the weed to spread quickly to new areas. Seeds can be carried by birds, animals, humans, wind and water, depending on the species of weed.
Weedy species are usually quick-growing, and rapidly colonise areas disturbed by fire, human activity, or over grazing by livestock or animal pests. Their quick growth rate allows them to out-compete native species for resources such as sunlight, nutrients and living space. The weed’s new home is usually free of the pests and diseases that kept their population in check within their native habitat, allowing numbers to expand until the plant becomes a problem.
Some introduced species that are established but have not yet spread widely are known as ‘sleeper’ weeds – they may have the potential to become a problem if conditions change. For example, the introduction of an appropriate pollinator or a change in climate could cause a relatively localised weed to become a widespread problem.
Many Australian species have the right characteristics to become weeds if introduced to a new part of the country, or if exported to foreign soil. For example, bluebell creeper, a climbing vine native to Western Australia, has become a weed in parts of southern Australia. It has infested hundreds of hectares, and in some places now makes up 60 per cent of the plant cover.
Even that iconic Australian tree the eucalypt is a weed – introduced to California 150 years ago for their wood and medicinal properties, they now form monoculture forests that exclude most native flora and fauna.
Boxes
Box 1. Cash for weeds
Box 3. Prickly pear – a biocontrol success story
Related sites
Don't grow Australian plants!
(Australian Society for Growing Australian Plants)
Guests and pests – Australian plants overseas
(Australian Society for Growing Australian Plants)
Posted February 2006.