Weeds and Bushcare News
Blue Mountains Under Attack
a Media Release from the Co-operative
for Australian Weed Management
March 30, 2005
Australia's beautiful Blue Mountains are one of the invasion beach-heads for a devastating assault by alien plants which, in places, are starting to take over the native landscape.
The qualities that make the Blue Mountains one of Sydney's iconic beauty spots both for locals and overseas visitors also place them at particular risk of plant invasions, a senior plant scientist warned today.
Dr John Hosking, of the Co-operative Research Centre for Australian Weed Management and the NSW Department of Primary Industries, said that the more researchers looked, the more plant invasions they were discovering.
"In NSW alone in the past four years we have identified more than 120 alien plants that have either naturalised into the native environment or are in the process of doing so," he says. The invaders include garden favourites like Agapanthus, various Pittosporums, Juniperus, Cistus, Erica, Ajuga, Arbutus and Clematis, certain pines, cypresses and elms - and even native Australian plants from interstate, like WA kangaroo paws.
"The Blue Mountains resembles the tip of a very large iceberg. It is one of the most likely areas for new weeds taking off, because it is accessible, populated, has many visitors and a range of climates and soil types. These together create many opportunities for invasive plants to establish.
"The sandstone country is a harsh place for plants to live, but nevertheless alien plants from places like South Africa are now getting a firm foothold." The Agapanthus, beloved of Australian gardeners, is emerging as a potential weed threat in parts of NSW and Victoria because of its hardiness and drought resistance.
"In the Blue Mountains, the ledges below the Three Sisters lookout are full of Agapanthus, which has taken over from whatever natives were there before," Dr Hosking says. "It may look pretty, but it is no longer a truly Australian landscape."
Researchers are currently recording around 30 'new' naturalised plant species in NSW alone every year. Some may be totally new records, and others have merely been identified for the first time.
The risk, Dr Hosking says, is that an invasive plant can lurk in the background, unnoticed, for years - and then increase rapidly when conditions are just right: when the landscape is disturbed, the climate changes or its seed is carried by humans, birds, wind or water to a suitable spot.
Particularly vulnerable, he says, are the river valleys in places such as the Blue Mountains, where seeds and plant fragments can be easily spread by water and find fertile ground to grow in. High levels of nutrients from sewage and land runoff are exacerbating the problem.
Among other invaders of concern is Coolatai grass, Hyparrhenia hirta, originally introduced from South Africa in the 1920s to prevent erosion, and which has since taken off across large swathes of NSW, from the northwest slopes and tablelands to coastal areas and the Blue Mountains.
"Once it is established, you can't get rid of it," says Dr Hosking. "It likes fire, and herbicide is just too expensive. It is very aggressive and grows so densely it is capable of taking over native bushland. It is very hard to deal with."
One of the goals of the Co-operative Research Centre for Australian Weed Management and NSW Department of Primary Industries is to try to discover what plant invasions are now taking place and where, to try to check the most dangerous ones before they become uncontrollable, he explains.
"There would be very little of NSW that is free of naturalised exotic plants today, and the problem in other states is proportional to their human population and the range of climates they offer for invaders to get a foothold."
Even if a plant does little harm where it is first introduced, human activity and natural dispersal enable it to 'explore' Australia in search of the perfect environment in which to multiply rapidly.
Dr John Hosking, Weeds CRC and NSW DPI
Phone: 02 6763 1129
Dr Rachel McFadyen, Weeds CRC
Phone: 07 3362 9388 or 0409 263 817