A crack herd of goats has been released at the Australian Botanic Garden at Mount Annan in an attempt to control an infestation of African olive, an aggressive woody weed.
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The mob of 18 wethers and four females is under strict control in a four-week trial at the Mount Annan gardens.
The goats are owned by a south coast company, Herds for Hire, run by Jim Shields and Elisabeth Larsen.
Mr Shields told the Herald they use "secret goat-training methods" to make sure the herd works together.
"We weed out the smarter goats that could get under the electric fence. We also remove the jumpers and anti-social goats. Most goats are very trainable, but a few aren't," he said.
African olive invades native bushland, "creating a dense shady canopy that excludes the growth of native understorey plants," says the NSW Department of Primary Industries.
The weed has been in Australia since the 1850s, when it is thought to have been introduced by sheep baron John Macarthur for hedging and as root stock for European olives, said Peter Cuneo from the Mount Annan gardens.
The introduced olive is now running rampant in the Picton-Camden area. Dr Cuneo, who is manager of Mount Annan's seed bank and restoration research, said there are now more than 2000 hectares of dense African olive in south-west Sydney.
"Critically endangered Cumberland plain woodland is particularly at risk from olive invasion," Dr Cuneo said.
The four-week trial has been approved by the NSW Minister for the Environment, Mark Speakman.
"This shows we're not kidding around on weed control," Mr Speakman said.
"The spread of the African olive in the gardens is a serious issue and I'm very happy to look at innovative approaches to improving our natural environment."
Jordan Scott is the supervisor of natural areas and open spaces at the Mount Annan gardens. He said the impact of the African olive shouldn't be underestimated.
"It's not just the loss of plant diversity and productivity on farm land. The removal costs are also prohibitive," he said.
Mr Scott said that 80 hectares of the 416-hectare garden had been overrun by the olive.
"We have reduced this to 40 hectares through mechanical and physical methods," he said.
Mr Scott said the goats, which are South African boer goats, will lighten the load of the work containing the olive. "And it's so nice just hanging out with them," he said.
The Mount Annan garden uses its seed bank to restabilise the cleared land with native grasses. Dr Cuneo said it takes three years to establish vigorous native grass cover.
"The goats are eating all the leaves and fruit and some of the branches. After they've gone we can go through and treat the olive stumps with herbicide," Mr Scott said.
The goats are contained in 2000-square-metre pens with an electric fence.
"Before we put them out to work, we train them to keep them away from the fence, which has about a quarter a lethal dose of electricity," Mr Shields said.
Ms Larsen, who has been monitoring the herd at Mount Annan all week, said: "They are going great with the olives. They love it. They chew all the nuts - eating them like lollies."
She said using goats had numerous advantages: they reduce the need for chemicals and can access areas out of reach of mechanical or manual clearing.
Ms Larsen said after her goats have cleared an area it is "like a cold fire has gone through".
Before coming to Australia to study in the 1990s, Ms Larsen was a heritage milkmaid in the Norwegian mountains, where she learnt special calls for her cows. She has adapted that to call in her goats.
Mr Shields said it's not a great idea to try this at home. "It might look easy to run the goats, but we spend time training each one."
He said it costs about $300 a day for the goats to munch away, clearing weeds or reducing fire hazards. But you have to pay the cost of getting them there, too.
smh.com.au
