Precious Mackenzie

Dean Baigent-Mercer says bringing water to one of the driest places in New Zealand would be a huge mistake.

In the rain shadow of Aoraki lies a vast inland basin with scorching nor’westers in summer and ground-heaving frosts in winter.

Around 10,000 years ago the Mackenzie Basin in South Canterbury was covered in ice. Glaciers ground and shifted great volumes of broken rock seaward. When the Ice Age ended, glaciers melted, leaving giant mounds of broken rock, “kettlehole” seasonal wetlands where huge lumps of ice melted, and vast gravel fans.

These and other glacial landforms each became inhabited by a range of specialised plants and animals. In pre-human times the Mackenzie Basin was a mosaic of beech, tōtara and matai forests, woody shrublands of bog pine, coprosma and prickly matagouri, and its distinctive bronze tussock grasslands.

The dry vegetation burnt easily. Lightning strikes, fires lit by Māori and later pastoral farmers have left only tiny remnants of native forest and caused the short tussock grassland to dominate. Few people would think of tussock as a long-lived plant but here it is a true survivor - some of the tussocks in the Mackenzie Basin are older than your grandmother.

Despite a wave of extinctions among its plant and animal life since human arrival, the ecology of the Mackenzie Basin remains outstanding in its uniqueness. Here are some of the last and most extensive remaining areas of undeveloped inter-montane basin floor ecosystems in New Zealand.

"The Mackenzie Basin's a bloody desert!" one high country farmer told me, which isn’t far off the mark. With less than 600 millimetres of rainfall a year, it is one of the driest parts of New Zealand, and is as dry as many parts of Central Australia. But although the vast drylands of the Mackenzie Basin may look barren, they are extremely rich in native plants, lizards and insects. Life here may also appear harsh and tough, but it is very fragile.

The Mackenzie Basin is home to 39% of Canterbury’s threatened plants, including 32 species listed as threatened, and another 59 plants in the “at risk” category.

You've got to get on your hands and knees to really appreciate a lot of what lives here. Entomologists have mapped the distribution of insects and spiders and the plants they live on and found their ecosystems and composition change remarkably with altitude and rainfall levels in the Basin.

Species of spider, weta and moths which exist only in the Mackenzie Basin have recently been discovered. Both the Mackenzie Basin tunnel web spider and Tekapo weta live underground is soft soils and come out at night.

The open, undeveloped character of the Mackenzie Basin remains because most of the basin is still held in pastoral leases under the. Crown Pastoral Lands Act. Pastoral leases can’t be developed for uses other than grazing, so leases provides much stricter controls than if these lands were in freehold ownership and subject only to the weak protection of the Mackenzie District Plan.

Department of Conservation botanist Nick Head says the undeveloped basin floors are highly significant as some of the last remaining examples of previously widespread ecosystems and biodiversity. “And despite being historically overgrazed these ecosystems are resilient. Even the most depleted will recover if managed sympathetically”, he says.

The process of tenure review, which leads to some parts of pastoral leases becoming conservation lands while other parts pass into private ownership by the former leaseholders, has led to a stand-off over the conservation of these areas. Farmers want ownership and irrigation development of the same areas that conservationists and scientists have argued need protection for their unique conservation and landscape values.

All too often, tenure review decisions have handed these fragile basin lands to farmers, with public conservation land assigned to mainly mountainous areas that are less useful for farming. This means that already rare habitats are being wiped out or severely reduced, compounded by the rapid expansion of irrigation of the naturally dry basin.

The Department of Conservation would like to see a “Drylands Park” covering about 30,000 hectares in the heart of the MacKenzie Basin. This idea was backed by the Parliamentary Commissioner for the Environment, who reported that of the South Island’s network of high country parks, only the proposed Mackenzie Basin Drylands Park is predominantly at low altitude, so would be a valuable addition to the range of ecologies represented.

The biggest threat to these drylands is water. Applications have been made to take more than 164 million cubic metres of water from high country lakes and rivers to irrigate and cultivate 27,000 hectares of the MacKenzie Basin.

This water grab would turn one of New Zealand’s most distinctive and well-loved landscapes into a replica of the Canterbury Plains, and wipe out some of our rarest and most distinctive native ecosystems. “Just add water” would be a recipe for disaster, putting at risk:
• 91 species of threatened and ‘at risk’ plants that rely on the naturally dry habitats of the Mackenzie Basin.
• Lakes Tekapo, Pukaki, Ohau and Benmore, which could be affected by algal blooms caused by farm nutrient runoff from the expansion of agriculture.
• The grand entrance to the multi-billion dollar high country tourism industry, including scenery which is a major drawcard for international visitors.
• The natural habitats and flows of numerous high country rivers and streams from which the water would be taken.
It would also bring industrial-scale farming to the Mackenzie Basin, turning the burnt brown landscape bright green, and strewing it with livestock and huge irrigators – a big turn-off to the tourists who are drawn by the vast, dry, empty landscapes, bringing with them billions of dollars in tourism revenue.
The attraction of a drylands park and a “Great Cycleway” from Geraldine to Mt Cook would be a much more appropriate and sustainable use of the landscape.
All sides agree that the Mackenzie must be better managed. But the visions for its future are poles apart.

If we succeed in protecting the Mackenzie Basin for its natural values people in the future will look back and see how perilously close we came to polluting lakes, causing extinctions and destroying our iconic landscape assets - all for the short-term gain of a few.
In coming months, expressions of public support will be essential to protect the Mckenzie Basin from disastrous political decisions. In a country so widely blessed with adequate rainfall to meet the needs of our communities and agriculture, our rare drylands should not be sacrificed.

Oasis in the desert

More than six metres of rain falls each year around Aoraki/Mt Cook, contrasting sharply with the 0.6-0.8m that falls in the MacKenzie Basin.

As rain in the mountains rushes to the Pacific Ocean, water emerges as freshwater springs, tributary streams and rivers. The rivers pool at Lakes Tekapo, Pūkaki andŌhau, draining on to Lake Benmore, then converge as the Waitaki River and run to the sea.

These MacKenzie Basin water bodies are oases of life.The black-fronted tern, black stilt, wrybill plover and black-billed gull are some of the distinctive braided river birds that rely on clean water and strong river flows.

So do many native fish, such as the lowland longjaw galaxias, which is New Zealand’s most threatened native fish. It shares the same dubious ranking for threat of extinction as the kakapo:nationally critical. The slender pencil-like fish is 75mm long and known from only seven populations. They require a 100% pure habitat at the head of a spring.

This freshwater life is at risk from proposed large-scale development of the Mackenzie Basin, which will change silt and nutrient levels. Lakes Tekapo, Pūkaki, Ohau and Benmore are at risk from the degradation and pollution seen elsewhere nationally.