A non-native goat-like animal is destroying New Zealand’s fragile alpine regions, and government culling has been unable to keep up with its population booms.

The Himalayan tahr was introduced to New Zealand in 1904 as hunting game for sports shooters, and has thrived in the rugged, alpine environment of the South Island.

The tahr’s significant weight and solid hooves are destroying precious snow tussock in sub-alpine regions. Numbers have reached 35,000, despite a government tahr control plan committing to keep numbers at 10,000.

As well as trampling native flora, tahr also snack on threatened alpine vegetation such as the the Mount Cook buttercup, the scree buttercup and Ranunculus acraeus.

“Tahr are social animals and can move in large groups browsing alpine herbs, tussocks and shrubs,” said James Holborow, from the Department of Conservation (DoC).

“They have a patchy effect across the landscape, but large groups of animals can transform tall tussocks and sub-alpine shrublands to a grassy turf or bare ground.”

Last year hunters, helicopter pilots and government conservation staff joined forces in a controversial attempt to control tahr numbers, with 12,000 animals shot since July 2019.

The tahr-control plan has caused tension among the outdoor community in New Zealand. Many hunters have protested at the government killing their favourite game targets, as have some animal rights activists.

In a petition objecting to the tahr cull, hunters accused the government of “destroying more than 100 years of New Zealand heritage and culture”.

Capitulating to objections, the government reduced their initial target from 17,000 to 10,000, but says further culling is necessary to save the mountains.

Ingrid Gruner, a DoC ecologist, said the changes tahr made to alpine areas were dramatic and “heartbreaking”, with Zora canyon on the west coast of the country’s South Island a prime example of the destruction wrought by the animals, who are native to India and Nepal.

“It’s heartbreaking to see the change over time,” Gruner said. “When we last visited the Zora canyon, it more closely resembled a rough paddock than tall tussock grassland.

“Tahr are a relatively heavy animal and when they mob together they compact the ground. Their trampling creates tracking, opens up the vegetation and exposes soils, potentially leading to erosion. Their urine and faeces act as fertiliser changing the nutrient status of the soils. All this can have profound and long-lasting effects on the local ecosystem.”

Due to the slow growth in cold temperatures and the fragility of alpine vegetation, it would take a long time to restore alpine regions affected by tahr, Gruner said.

The president of New Zealand’s Federated Mountain Clubs, Peter Wilson, told Wilderness magazine that tahr control had historically been grossly underfunded, and the out-of-control population was threatening some of the country’s rarest and most pristine wilderness areas.

“This is what happens when you underfund conservation,” Wilson said. “I think reducing the tahr population needs to be done in a staged way. Otherwise, it will set back country relations with hunters by a decade.”

Under the Labour coalition government, the DoC received a major funding boost in last year’s budget, and will employ 100 new staff this year.