Himalayan tahr were introduced to New Zealand more than a century ago for sport, and they remain a popular target for hunters today. But hunting hasn’t stopped tahr numbers ballooning to an estimated 35,000 on public conservation land – far too many for the fragile ecosystem to take, writes DOC’s threatened species ambassador, Erica Wilkinson.

If you ask a Department of Conservation scientist what their favourite experience in a national park is, make sure you have a spare half hour. In Fiordland, it might be South Island robins pecking at your boots and looking up curiously, or the silhouette of long-tailed bats foraging in the sky at sunset. In Aoraki/Mount Cook you could spot a giant wētā crawling behind your bivvy or see juvenile kea learning to play. It would be epic thunder and lightning storms, beautiful starry nights, huge avalanches and rock falls.

National parks are our mainland insurance policy. They’re what more of New Zealand could look like, because they’re what New Zealand did look like. They’re like a film on pause, the characters currently spared the tragedy at the end of act two. With the greatest protection status of all conservation land, our national parks are bursting with species that, in some cases, wouldn’t still be here if not for these fragile green havens.

Globally, just over 100 countries boast parks like ours. Since Tongariro National Park was established in 1887, we have added 12 more national parks across the country, each with its own unique characteristics and ecosystems.

And now that our borders are closed and we can’t take the family to the Gold Coast, we have the chance to rediscover the places that we showcase to the world but sometimes forget – the national-scale version of how well we got to know our local walks during lockdown. There are more than 30,000 square kilometres of diverse, natural scenery on our doorstep just waiting for us to explore. They hold the remnants of our national identity, too. New Zealanders define ourselves by our love of the natural world. Today, however, 87% of New Zealanders live in urban areas. We’re more likely to recognise a blackbird or sparrow than a robin or kōkako. We can spot pine trees or gorse anywhere, but would have to Google kānuka. A lot of us experience a disconnect between our vision of New Zealandness and what we experience. That makes areas like national parks even more important.

National parks legally need to be preserved and maintained for generations to come. DOC is responsible for protecting them against the effects of a warming climate, invasive pests and predators, and habitat destruction. It’s a big job. The balance of an ecosystem can be a very fragile thing. One species taken out, or on the flipside becoming too dominant, can lead to a complete ecosystem collapse.

Take Yellowstone National Park, the first such reserve in the United States. In the early 1900s the government had the wolves in the park hunted to elimination to protect the elk. This set off something called the trophic cascade. With no apex predator to fear, the deer and elk populations boomed. This resulted in over-grazing, particularly of willows and other vegetation needed for riverbank structure – which led to heavy erosion.

With no wolves preying on them, elk could intensely graze along riverbanks, and the vegetation disappeared. Beavers lost the willows they needed to build their dams. Birds had no trees tall enough to safely nest in. Without beavers’ dams, fish weren’t thriving. As fish numbers dwindled, so did bears and foxes that relied on fish for food. Hundreds of species started to decline.

When wolves were finally brought back in the 1990s, the ecosystem eventually rebalanced, and the species bounced back. One beaver colony became nine.

We are facing a similar issue in New Zealand right now.

In 1904, Himalayan tahr were brought to New Zealand for recreational hunting They were released in Aoraki/Mt Cook and, with no natural predators, quickly adapted to our alpine environment. Their population has boomed, and today tahr numbers exceed the level that the alpine environment can cope with. Tahr were picked up and put into our fragile ecosystem where species have not evolved with defence mechanisms to deal with mammals like this. In other places, plants might develop toxins or spines to discourage browsing. It hasn’t happened here. In autumn 2019 there were an estimated 35,000 tahr on public conservation land alone, where the maximum legally is 10,000 across all types of land. DOC, commercial hunters and contractors have since reduced their numbers but tahr have become a major threat to these alpine ecosystems. DOC is required to reduce tahr populations to the lowest possible densities in national parks to protect our species.

Just like we saw in Yellowstone with deer and elk overabundance, tahr can have a devastating effect across the landscape when their numbers are not controlled. As social animals they move in herds or mobs as they look for food. They are heavy, and compact the ground as they move, turning what was tall tussock grassland into something resembling a rough paddock no longer able to provide habitat or grow vegetation that our native species have evolved to depend on. Their faeces and urine even change the nutrient status of the soil, affecting what can grow there.

It can take decades to save an ecosystem, but not long to destroy it.

You only need to look at areas tahr or deer have been in at high densities to realise the fight our native species are facing on top of everything else. It’s good to be clear here: there is no plan to eradicate tahr, but we need to do this control work in order to protect our native species already exhausted from battling stoats, possums, and rats.

Believe it or not, nobody likes killing things. That is not a fun part of the job. You have to be outcome-focused, constantly reminding yourself of the conservation end goal you’re heading towards. We have a duty to protect our unique and ancient native wildlife and our reality is a huge number are on the fast track to extinction. I’m for our native species first and foremost, and in the 148,000 ha of national parks, our native species need to come first.