The Hidden World of the Ashburton Lakes

Forest and Bird, Issue 305, 1 August 2002, Page 28

The Hidden World of the

Ashburton Lakes

ANN GRAEME

DON GEDDES

explores a high-

country basin under threat.

t is scarcely two hours’ drive from Christchurch to the Ashburton Lakes, hidden in the front ranges of the Southern Alps. The ruler-straight roads lead across the orderly patchwork of the Canterbury plains, to wind through a gorge in the foothills and, suddenly, the landscape of the Ashburton Lakes opens up. Here a vast basin of tawny tussock is ringed with mountains under a pewter sky. Scattered like jewels across it are the 12 lakes and, between them, the braided rivers that rise from the snows of the Southern Alps and the Arrowsmith Range. Guided by Ashburton Branch members, Peter Howden, Bill Hood, Edith Smith and Noeline Sinclair, my husband Basil and I came to see and learn about this area and its natural wonders. The Ashburton Lakes/Hakatere basin has been carved and filled by ice age glaciers over the last two million years. As the glaciers retreated they dropped, like careless giants, huge slabs of ice which melted to form the basin’s ‘kettlehole’ tarns, while hollows behind the glacial moraine became the larger lakes. The glaciers also carved out the

valleys where now flow two braided rivers, the Ashburton South Branch and the Rangitata. Braided rivers are special. They are found only in northern Asia, Alaska, Iceland and New Zealand, and are created by the chaos of melting glaciers. In springtime the rivers fill with melted

snow and rage across their flood plains, tumbling and turning the rocks they have carried down from the mountains into the polished stones and boulders of the riverbed. It is an unstable world where plants which have rooted between the stones are torn up by the next flood. But it is also a world where insects flourish

briefly and where rare birds such as wrybill and black-fronted terns come to nest during the summer. The Ashburton is one of the most important of Canterbury’s braided rivers for birdlife. It supports more than 50 species including the threatened wrybill plover, banded dotterel, black-fronted tern and the highest recorded numbers on any Canterbury river of the vulnerable black-billed gull. But the ambitions of farmers and

power generators threaten both the Ashburton and the Rangitata River. (See Forest ¢& Bird, May 2001.) Ashburton Forest and Bird members go again and again to meetings about the Ashburton River to put the case for protecting the river’s natural values and ecosystems. Water is valuable, sought after to irrigate the dry Canterbury plains. Already the lower Ashburton River is one

of the most heavily modified river systems in New Zealand. A succession of water intakes sucks out some 60 percent of its water by the time the river reaches the town of Ashburton near the Canterbury coast. So far, above the Ashburton gorge, the upper South Branch of the Ashburton and the lakes are unaffected by any major water takes, but this could change. Proposals are afoot for a $98 million hydro-generation and irrigation scheme. This would mean building a 62-metre-high earth dam at the downstream end of the gorge. The dam would create a 585-hectare-lake which would flood kilometers of braided riverbed, back into the Hakatere basin. Such a scheme would not only violate the landscape, it would tame the water flows, restraining the downstream floods

and freshes which bring the chaos on which the braided river ecosystem and its plants, insects and birds depend. It is these massive floods which create the braided character of the river with its pattern of gravel bars and channels. Stability is the enemy that would let river banks consolidate and confine the shifting river braids. Stability would help weeds survive because there would be no floods to sweep away the colonizing plants. Thus bird, fish and insects habitat is lost. Downstream, where the Ashburton and Rangitata burst through their gorges onto the Canterbury plains, willow, lupins, and broom are already choking the riverbeds, usurping the silvery native cushion plants and the ‘dead sticks’ daisies. The open stony riverbed and its banks are becoming a shrub land of weeds, no longer a haven for nesting birds but a cover for feral cats, stoats, and other mustelids. ‘The country is mortgaged to weeds, says Peter Howden. As a farmer, he knows the endless cost of combating weeds, and how any downturn in farm returns could invite the cost-cutting that allows pasture

weeds to escape into the tawny landscapes and braided river beds. Apart from a limited infestation of broom in the Potts River, some willows on the lake margins, scatters of wilding pines and the ever present hieracium, weeds are not obvious in the Ashburton Lakes landscape. This is thanks to the vigilance of some high country run holders and the ‘No Green Needles’ workdays organised by Environment Canterbury to remove wilding pine trees. Ashburton Forest and Bird members tramp across country to

weed or, with chainsaws, to destroy wilding pines before their seeds can spread. In this brown and gold landscape the alien green of pine, willow and broom make the larger weeds easy to spot. For Ashburton Forest and Bird, the Ashburton Lakes is their special ‘backyard’. They come to weed and to tramp and to enjoy the magnificent mountain landscapes. For 18 years now, members have also been part of an annual winter wetland bird count, organised by a Department of Conservation scientist, Dr Colin O'Donnell, and the Ornithological Society. Dr O’Donnell has an encyclopedic knowledge of these braided rivers and their birds. He has documented the decline of all the native species that nest along the length of the Ashburton River; a decline he attributes to water abstraction in the lower river and weeds and predators invading the open, stony riverbeds. But the black-fronted terns, the black-billed gull, the banded dotterel and other special species are still thriving on the South Branch of the Ashburton, making it even more important to keep this river bed free from weeds and safe from dams and irrigation proposals.

The Ashburton Lakes

Each of the 12 Ashburton lakes has its own character. Lake Emily is shallow, small and swampy, the Maori Lakes mirror their extensive raupo wetland, and the largest, Lakes Heron and Clearwater, are reputed to be the most beautiful. A 1986 survey report for the Protected Natural Areas programme described Lake Heron as the most important lake and wetland complex for wildlife in the South Island high country. Both it and Lake Clearwater are wildlife refuges, recognizing the great diversity and number of birds they support. They include the endangered crested grebe, New Zealand scaup, shoveler, grey duck, grey teal, paradise shelduck, Australasian bittern, Australian coot, black swan and marsh crake as well as large numbers of pukeko, black and little shags and introduced Canada geese. Winter surveys have recorded up to 6000 birds on the Ashburton lakes. Here too, as on the South Branch of the Ashburton River, the native birds have not declined. Lake Clearwater is also home to a cluster of around 200 small baches. Although powered boats are prohibited,

people windsurfing, yachting, canoeing, and fishing disturb the waterfowl during the summer. Ironically it is the introduced willow trees weeping over the water that provide some privacy and support for the floating nests of the crested grebes. Over the years, a long-time bach owner and Forest and Bird member Neville Adams, and his family, have cared for the nesting grebes, fencing and trapping the banks around their nest sites and teaching the bach community about the rare birds in their midst. (See Forest ¢& Bird, November 1988). The outstanding landscape, geological and wildlife values of the Hakatere Basin, its lakes, and the South Branch of the Ashburton have been recognised and described since 1867 when the pioneer nature conservationist T. H. Potts took up the Hakatere lease. But progress in achieving effective protection for the area has been glacially slow. Lake Emma and part of the Harper Range have been surrendered because of freeholding. They, and some of the Arrowsmith Range, are now conservation land. Lake Heron and the Maori Lakes are nature reserves, Lake Clearwater is a wildlife refuge and some of the higheraltitude terrain is ‘retired’ from grazing. That is about all of the Hakatere Basin and Ashburton lakes landscape that has any protection. The rest is pastoral lease land — leased long term from the Crown for farming. The Department of Conservation’s Canterbury Conservation Management Strategy (2000) notes that the Ashburton Lakes merit a water conservation order but, frightened by likely opposition from the farming community and the prospect of a political hot potato, the Department has done nothing to progress an application. Erewhon and Mesopotamia stations in the upper Rangitata — their names are the stuff of legends — are just two of the larger pastoral leases in the area. They, and a handful more around the Hakatere basin, graze vast domains stretching from the valley floor to the mountain tops. While farming has preserved the largely unbuilt and expansive nature of the basin, decades of grazing, oversowing and top dressing continue to change and degrade the indigenous vegetation. ‘Improved pasture’ to a farmer means grassland that, through fertilizing and over-sowing with palatable exotic grasses and clovers, will support higher numbers

of stock and provide better monetary returns. Inevitably ‘improving’ the pasture is at the expense of its natural character, native tussock communities and particularly, their invertebrates. Despite more than a century of grazing, however, the landscape retains a strong natural and indigenous character, partly because of the tenacity of the native species. Grassland covers the basin. In upland areas tall snow tussock and hard tussock grow with snowberry and the spiky Aciphylla or Spaniard. Lower down, introduced pasture species like browntop mingle with indigenous short tussock, mountain daisies and gentians. In wetter areas, red tussock and sedges grow. Around the margins of some of the lakes and kettlehole tarns grows a special turf community with a rich diversity of tiny, and sometimes rare, plants. There is scarcely any beech or other forest, a legacy of glaciation and early Maori burning. Wetlands are vulnerable to grazing and draining. While Lake Emma and the Maori Lakes are fenced and protected from stock, other wet places are drained or trampled and pugged by cattle so that the wetlands dry out and shrink. This encourages exotic grasses and weeds to displace the red tussocks, the icons of the natural wetlands. To admire the red tussock wetland of the basin — and in the teeth of a nor’ wester — we battled our way around the shore of Lake Clearwater. The nor wester is yet another element in this wild landscape, and, like a living force, it was making the grasses stream and the white-capped waves pound upon the shore. We were stunned by the violence of the wind. Neville smiled, ‘This isn’t blowing, he said. ‘If it was really blowing, you wouldn’t be standing up!’ Such a powerful landscape inspires a reciprocal powerful love by the people of the high country, be they runholders, fishers, or Forest and Bird members. Ashburton Forest and Bird Branch seeks better protection for the landscape they love and this is what they want: 1. A water conservation order over all 12 Ashburton Lakes and the streams that flow into them, and on the South Branch of the Ashburton River to well below the Ashburton Gorge. This would allow the existing water takes to continue but would prohibit any more water abstractions or any dams on the river. 2. A weed control plan involving runholders, councils and conservation

groups that would target weeds everywhere — on pastoral lease land, on roadsides and on the river beds. 3. Better protection for vulnerable native species, communities and landscapes through the tenure review process.

ANN GRAEME is the co-ordinator of Forest and Bird’s Kiwi Conservation Club.

is a committee member of Ashburton

Forest and Bird. Thanks to Forest and Bird field officer, Eugenie Sage of Christchurch, for help with this article.

Riverbed birds

Baked by the sun by day, frozen at night, at the mercy of storms and floods, a braided river seems a strange and bleak nesting site. But it is much sought after. Every spring, wrybill plovers and banded dotterels fly south from the North Island and black-billed gulls and black-fronted terns fly inland from the coast to stake out a nest site, bereft of cover. ‘In springtime the silver cushion plants are flowering and they're alive with insects, says Peter Howden. ‘Great tucker for the parents to feed their chicks.’ And in the water the bent beak of the wrybill probes between the stones for the larvae of mayflies, stone flies and Dobson flies. They in turn are eating algae, nourished by the snow-fed waters.