Citizens recruited to fight the weed invasion

Australians have been urged to defend their native landscapes against an insidious invasion of slow-spreading weeds.

A new study by Dr Joe Bennett from the ARC Centre of Excellence for Environmental Decisions (CEED) and The University of Queensland reveals that exotic weeds that spread slowly and are unable to travel long distances can potentially cause just as much damage to native plants as fast-spreading weeds.

"These weeds are known as 'short dispersers', and while at first they appear to be rare and slow-spreading, they can eventually become harmful pests," Dr Bennett says.

"Our study shows that some of them are merely taking longer to establish themselves. Once they do, they may become even better adapted to the environment than native plants and out-compete the natural vegetation for water, sunlight and nutrients. They may not be fast-spreading, but they're tough and resourceful.

"Examples of these slow growing weeds include the creeping yellow cress, the Chinese violet and the giant tropical salvia. Small pieces of these weeds can grow into new plants and spread over large areas."

Dr Bennett says that short dispersers aren't always as obvious as the fast-spreading weeds, and are often 'garden escapees' or rare new plants along roadsides. "This is why citizens play a crucial role in preventing these weeds from assaulting our native landscapes. We need their vigilance to help spot, and report them.

"There are about 10 new plants reported in Australia every year. While not every new species will be invasive, being able to predict and eradicate slow-spreading weeds before they get out of control can save us millions of dollars or the loss of a treasured native landscape."

He says there are several ways to predict whether a short disperser will be invasive: "They are often like the native plants, in that they can tolerate bad weather or droughts, or have special ways of outcompeting or suppressing native species. Checking if the weed has been invasive elsewhere is often a good gauge.

"Local councils can educate the public about these weeds and encourage them to report new plants they find spreading along roadsides."

"In the meantime, we should garden with native vegetation – instead of exotic ones – and watch out for plants that grow beyond our backyards, such as ivies, lilies or bamboos," Dr Bennett says.

"It's also important that we bag and dispose our garden waste properly, instead of dumping it somewhere – local councils usually have the information on how to do so."

"If a weed appears to be rare and confined, that doesn't mean that it's harmless. In our study, a lot of the recent 'invasives' turned out to be plants that people have had in their gardens for years," Dr Bennett cautions.

"The bad news is more new species will probably keep arriving, but the good news is we have time to focus on some of these slow-spreading weeds and get rid of them before they become uncontrollable."

The study "Abundance, rarity and invasion debt among exotic species in a patchy ecosystem" by Joseph R. Bennett, Mark Vellend, Patrick L. Lilley, William K. Cornwell and Peter Arcese is published in the journal Biological Invasions. See: bit.ly/SqYsJ1.