More than 400 of Australia’s threatened species of plants and animals are at risk of extinction from weeds.

The recently released 2006 State of the Environment (SoE) Report has highlighted the major threat posed by introduced plants to Australian fauna and flora, and lists a range of native species directly threatened by invasive plants. 

It follows hot on the heels of Australia’s first-ever report quantifying the impact of alien plants on Australian biodiversity, produced by the CRC for Australian Weed Management. That report found invasive plants are the biggest threat to the survival of native species after land clearing.

The Weeds CRC study also implicates Australian householders directly in the loss of native species, pointing out that two thirds of the most damaging plants entered the country as ornamentals and escaped from parks and private gardens.

Among the native plants and animals directly threatened by weeds, the 2006 SoE Report lists: 

- the mountain pygmy possum in NSW and Victoria
- the tussock skink in Tasmania
- spiked rice flower and hairy quandong in NSW
- the spider orchid in SA
- the Richmond birdwing butterfly in Queensland and NSW
- the wing-fruited lasiopetalum in WA
- the button wrinklewort in ACT and NSW.

 “We’ve always strongly suspected weeds were a factor in the decline and loss of native species, but until our research was completed there was no clear confirmation,” the CEO of the Weeds CRC, Dr Rachel McFadyen says.

The CRC study, by Aaron Coutts-Smith and Paul Downey of the NSW Department of Conservation and Environment and commissioned by the Weeds CRC, looked at the threats to 945 threatened species, populations and ecological communities, and concluded invasive plants were a major factor affecting 419 of them. These included 279 native plants and 62 native animals.

They found that the main threats came from 127 invasive plants, of which the worst were lantana, bitou bush, blackberries, kikuyu and Scotch broom.

Of these 127 invaders, 82 gained their foothold in the Australian environment after escaping from parks, gardens and ornamental collections. Between them, these ‘garden escapes’ threaten at least 190 native species in NSW alone and maybe as many as 300.

Fifty-six of these ‘killer weeds’ are still available for sale in garden centres across Australia, despite the fact they have previously been identified as highly invasive.

“This study, more than any yet, highlights the responsibility of the home gardener and the garden centre in helping to protect our native species from extinction due to an alien plant invasion,” Dr McFadyen says.

“Many of these plants look beautiful - and harmless - in a small pot. But when they get loose in the landscape they cause havoc, strangling and smothering native vegetation and depriving our native birds and animals of their main sources of food.”

Since European settlement an estimated 27,000 plant species have been introduced into Australia – almost twice as many as existed here before. Three thousand of these have adapted well to the Australian landscape and are now ‘naturalised – i.e. they successfully reproduce in the wild.

Dr McFadyen says both reports are a big wake up call to all Australians to take greater responsibility for the survival of our native landscapes, and its fauna and flora.

“This is a problem we can all do something about,” she says. “We need to become educated consumers of plants. Before we buy a plant at the garden centre or market we should first check whether it has a record for invasiveness, no matter how pretty it looks.

“Garden centre staff need to become the local experts in invasive plants”, says Dr McFadyen. “They have a brilliant opportunity to become part of the solution.”

“And we must take the greatest care in disposing of all plants and plant material from our gardens, in case it contains weed seeds or has the ability to regenerate.

“If we truly want our grandchildren to see a genuine Australian landscape in the future, we have to act now to stem this continuing invasion.”

Dr McFadyen warns there is a particular threat in the trendy decorative grasses and succulents which are now being planted in low-water-use gardens. They are naturally tough, and many are highly invasive in both agricultural and natural landscapes.

The Weeds CRC, which has been Australia’s leading scientific research centre in invasive plants and warned consistently of the importance and scale of the problem, has been told by the federal Government it will close as a CRC in 2008. Dr McFadyen says they are actively seeking other ways to keep this important work going.