Stalking a shady individual

Associate Professor Susan Laurance and her team of researchers from James Cook University have found that a shade-tolerant shrub from Brazil, Strawberry Guava (Psidium cattleianum), is exploding in abundance across their study sites on the Atherton Tableland. 

Strawberry Guava, named for its delicious fruits, has been listed as among the world's 100 worst weeds. In some tropical regions like Hawaii and Seychelles, it has already caused ecological havoc, replacing the endangered native forest. So far in Australia, it has gone largely unnoticed.

 “What makes this species so dangerous is its ability to outcompete native species by forming dense impenetrable stands,” Associate Professor Laurance said.

“In one highly infested site, Strawberry Guava made up more than half of all woody plants, forming an impenetrable monoculture and carpeting the forest floor in its abundant fruit.

"The impact this weed will have on the rainforests of Australia's Wet Tropics World Heritage Area is cause for great concern. It is highly tolerant of shade, which normally stops most weeds from invading dense forests,” she said.

Fellow JCU researcher Dr David Tng says one of the reasons the species is becoming so dominant is that it seems to have no natural enemies, so there is nothing to keep its population in check.  

"Understanding the ecology of Strawberry Guava is only a first step. We need to work out where it can potentially spread,” said Dr Tng.  "Given that Strawberry Guava is still a relatively recent problem in Australia, it may still be controllable if decisive action is taken now."

Dr Tng said the team had found some significant infestations of Strawberry Guava while working in the Tarzali area, but it was possible the pest would be found elsewhere in the Wet Tropics.