Weeds pose a major problem on offshore nature reserves, but could the means of controlling them cause more harm than the plants themselves?
That’s one of the questions UNE PhD student Kirsten Drew will be trying to answer for some of Australia’s most pristine and precious island environments.
Kirsten is about to begin sampling soils from islands off the NSW coast – South Solitary, Broughton and Big islands – and will make a brief trip to Macquarie Island on an Australian Antarctic Division resupply ship in March.
On all islands except Macquarie, the broad spectrum herbicide glyphosate (commonly sold as Round-up) has been used to manage weeds.
While it had been considered an environmentally safe chemical, reports of toxicity, leaching and resistance build-up to glyphosate have recently emerged. It can be toxic to aquatic organisms when applied at high rates, and has been detected in water run-off.
“There are real concerns that the application of glyphosate on heritage islands may be harmful to their unique and sensitive ecosystems, but almost no data is available to confirm or reject these concerns,” Kirsten said.
“We don’t know how persistent glyphosate is in the soil, how it degrades or whether it is leached out, especially on high-rainfall islands.
“It has been found to be toxic to microbiology in soils and possibly to fish and bird life. This means it could present issues for a range of wildlife.”
Kirsten’s research will compare the persistence, degradation and mobility of glyphosate in different climatic zones and soil conditions – from the subtropical South Solitary Island to subantarctic Macquarie.
On South Solitary – an important nesting habitat for several species of migratory and threatened seabirds and shorebirds – exotic perennial grasses, madeira vine and coastal morning glory are proving troublesome.
The same introduced plants are posing a threat to little penguins and shearwaters on Big Island, off Wollongong.
On Macquarie Island, the eradication of rabbits has changed the island’s vegetation and it is feared that winter grass and chickweeds will expand.
“Understanding how glyphosate behaves is very important because increased rainfall intensity is predicted on some of these islands under climate change,” Kirsten said.
“What I discover will immediately guide National Parks and Wildlife weed control strategies.”
Since 2012, UNE researchers have carried out two successive Australian Antarctic Division research projects on Macquarie Island to better understand the ecology and management of weeds that threaten native environments.