African gamba grass could invade up to 38m hectares of tropical savanna in northern Australia, causing “grave concerns” for fire management, a report has found.
In the Northern Territory, gamba grass has already taken hold and is fuelling regular and intense grass fires between the town of Batchelor and the Darwin rural area. The report, released on Tuesday by the Pew Charitable Trusts and the Environment Centre NT, said firefighting costs in that area had increased 30-fold in a decade.
Gamba grass fires can be up to 12 times more intense than native grass fires.
“You hear from volunteer firefighters who say you used to be able to handle a native grass fire by walking around. These days you need air support,” said Mitch Hart, the NT manager of the Pew Charitable Trusts.
Gamba grass was introduced into Australia in the 1930s as cattle feed. In the late 1980s and early 1990s it was actively cultivated and sought-after by top end graziers because it was easily established, drought resistant and adapted to hardy soils. The same characteristics also made gamba grass an aggressive weed and it is now classed as a weed of national significance.
Hart said gamba grass now covered about 1.5m hectares, mostly in the Northern Territory but also in parts of Queensland and Western Australia. He said the weed could expand rapidly.
“Gamba grass has the potential to invade all tall, tropical grass savannas in northern Australia,” the report says.
“It is estimated the potential invasion range is at least 38 million hectares. Gamba grass has rapid rates of spread, leading experts to believe it is merely a matter of time before it can realise its geographic potential.
“The rapid speed of gamba grass invasion from initial source paddocks in the 1990s to present distributions is of grave concern given its broad ecological tolerance.”
The report says up to 20% of Litchfield national park, near Batchelor, is covered by gamba grass. Alongside the threat to tourism and the increased fire risk, the report estimates gamba grass costs the Territory economy tens of millions of dollars each year.
The report warns gamba grass could threaten the burgeoning carbon farming industry, which has been lucrative for Indigenous enterprises.
“Many impacts of the invasion are open to potential valuation, for example, the cost of weed control, fire management of invaded areas, and loss of infrastructure. However, other impacts are harder to quantify but are no less grave. They include the radical transformation of natural landscapes, loss of ecosystem services, loss of cultural resources and traditional food sources, impacts on public safety and the health of firefighters and the general public,” the report says.
“Delay in action or insignificant investment in managing gamba grass will result in escalating costs of control [and] reduced economic returns from management actions.”
Hart said the Northern Territory government’s plan to combat the spread of gamba grass was under-resourced.
“On paper there’s a lot of good stuff, but if we’re going to do it the way we should, you’ve got to put resources into it,” Hart said.
