[ASC-media] Media release: spotting invaders from space

JCA Media jca.media at starclass.com.au
Mon Oct 16 12:53:48 CEST 2006

Cooperative Research Centre for Australian Weed Management

Media Release

October 17, 2006


A new eye-in-the-sky can pinpoint a single invading thorn bush from outer space.

Dr Roger Lawes, a CSIRO scientist working with the Cooperative Research Centre for Australian Weed Management, and Dr Jeremy Wallace of CSIRO are using images provided by the IKONOS satellite to map the devastating spread of prickly acacia (Acacia nilotica) across the continent's northern grasslands.

"The images are so precise we can see the advance of prickly acacias into the Mitchell grass country," Dr Lawes says. "This will enable us to take management steps to control the pest."

Prickly acacia was introduced to Australia from the Indian subcontinent as a shade and fodder tree. It became invasive when cattle were introduced to areas where it had become established, as they eat the seedpods and spread the seeds. 

Prickly acacia is one of Australia's Weeds of National Significance (WoNS) and costs the Queensland grazing industry over $5 million a year. It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.

It infests nearly seven million hectares - an area the size of Tasmania - and could cover the northern grasslands of Queensland, the Northern Territory and Western Australia if left unchecked. Even at medium densities, it halves the primary productivity of grasslands, interferes with stock mustering and restricts stock access to water. Control costs considerably outweigh its benefits as a shade tree.

Prickly acacia dramatically alters the ecological balance of grasslands and thereby threatens biodiversity, particularly in the Mitchell Grass Downs in Queensland, home to 25 rare and threatened animal species and two endangered plant communities. Infestations also have an impact on tourism and land use by indigenous people.

>From space, prickly acacia has a recognisable 'signature' that is picked up in satellite images.

"We have developed a tool using the latest remote sensing technology to detect the invader," Dr Lawes said.

"This gives us a reliable indication of what is happening over large areas. It can be used as an early warning system to detect new invasions. 

"If we detect a change in the index, we can have a look on the ground and take the necessary steps to control the outbreak."

The technique can also be used to monitor other changes in perennial vegetation across the landscape. 

"Invasive species can be difficult to manage and monitor. In the rangelands they can behave in unexpected ways," Dr Lawes said.

"Seed dispersal, the precursor to new adult plants, is highly erratic. The distance, direction of dispersal and propagation of new weeds are affected by variations in soil types, sudden heavy rains and variable river flows." 

He said the weed monitoring technology was developed using a combination of remote sensing, ground surveys and detailed data analysis. 

"Ikonos has a one-metre pixel resolution," Dr Lawes said. "Anything larger than one square metre can be detected. Acacia trees have a canopy of up to five metres, so individual trees are easy to see.

"This means that we can accurately count the number of trees in a given paddock."

For broader-scale work, Landsat images are used with a 25-metre pixel resolution.

Dr Lawes said that while the project results are yet to be published, the software behind the technique is available now to interested parties. 

Media Contacts:
Dr Roger Lawes, Weeds CRC, CSIRO Sustainable Ecosystems
07 4753 8537, 07 4753 8600, 0405 317 307

Peter Martin, Weeds CRC, 08 8303 6693, 0429 830 366

Images of Acacia nilotica available from Rita Reitano, 08-8303 6857, rita.reitano at adelaide.edu.au

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