Saline-loving Plants of Central Otago

Forest and Bird, Volume 21, Issue 1, 1 February 1990, Page 40

Saline-loving Plants of Central Otago

by

by Neville Peat

Few people place salt pans in a New Zealand landscape. But in the semi-arid, range-and-basin topography of Central Otago, saline soils do occur, harbouring distinctive plant and invertebrate communities, as Neville Peat, of Dunedin, reports. Wetts A RESPECTABLE COASTDWELLING (saltmarsh) glasswort like Sarcocornia quinqueflora doing in the Maniototo Valley, 70km from the sea? Savouring the salty soils, that’s what. Clumps of it spread out over ground that would otherwise be bare of vegetation, too Salty certainly for the ryegrass and clover which the farmer would prefer to see growing there. Central Otago once had extensive salt pans. Through cultivation, irrigation and oversowing, these areas are now much re-

duced in number and extent. But the most resilient of them survive, a few hectares or square metres here and there. They show up as patches of dirt, sometimes silky white. You might mistake them for random examples of wind or water erosion. But the plants around them know differently — small, ground-hugging, specialised plants and very distinctive. They tend to shrivel under the freezing winters but come again in spring. Probably the most distinctive plant of Central Otago’s saline areas is Atriplex buchananii, which spreads its small leaves and delicate stems across the most salty and arid-looking sites. The rarest plant of these salt-tolerant communities, however, is a native cress, Lepidium matau, a relative of the coastal Cook’s scurvy grass (Lepidium oleraceum). Only about 30 plants of the species have been found, and it is known from only one site — a sloping half-hectare on Galloway Station near Alexandra. Part of the site forms the shoulder of a road (Crawford Hills Road to Moa Creek). This plant's creamy flowers dominate the foliage in spring. L. matau rates among New Zealand's most endangered plants. Two related species, L. sisymbrioides and L. kirkii, less rare but nonetheless vulnerable, are also associated with the salty areas of Central Otago. Botanists recognised last century that salt pans harbour distinctive plant communities, but the entomological values of the saline areas of Central Otago were virtually un-

known until a scientist with the Department of Conservation in Dunedin, Brian Patrick, undertook a systematic survey of the most prominent sites in 1987-88. Mr Patrick, who is a moth specialist, rediscovered a species of moth which had been lost to entomology for 50 years — Paranotoreas fulva. A small day-flying moth with orange and grey wings, it is now considered by Mr Patrick to be the species most characteristic of Central Otago saline areas. Its larvae feed on Atriplex buchananii. Adults are often found "sunbathing" on the bare, slick earth. Several other moth species associated with the saline areas are found only in Central Otago. The study is fitting together the pieces of a distinctive ecology. Fauna linked to plants, plants linked to saline soils. But where did the salt come from in the first place? DSIR soil scientist Gary Beecroft, of Dunedin, says the salinity derives from the crumbling and weathering of the ancient schist and greywacke rocks of Central Otago and the Upper Waitaki, which also bears a few salty patches. The salts became concentrated and buried in the sediments of inland lakes which formed some 50 million years ago when the region was a peneplain. Then, while still a peneplain, long before the block mountain ranges were hoist up along fault lines, the region (or a good part of it) was flooded by the sea. Mr Patrick and others believe the salt-toler-ant plants endemic to Central Otago today

could be descendants of the plants which inhabited the old coastline, and it is possible some of the fauna might trace their origins similarly. As further evidence he cites the presence of case-moth species, Scoriodyta suttonensis, in Central Otago. Its larvae feed on algae on the conspicuous tors. The genus consists of seven species and is characteristic of coastal rocks. Four species are found around the South Island coast and two more in the Cook Strait areas. Since they have apterous females which never leave the larval case and the larvae feed on the same tor or group of tors, the species is effectively immobile and its occurrence in Central Otago may be the result of a marine transgression. The sea retreated, the ranges rose up, and over time, the salts deposited in the sediments were borne by water to the surface by the process of capillarity. Central Otago’s saline soils represent a soil type now rare in New Zealand, and according to Mr Beecroft, one which will soon disappear if left unprotected. He and fellow soil scientist Peter McIntosh are working in conjunction with DoC to produce a register of the best remaining sites,

including descriptions of their soils and geology. This register will provide baseline data for future monitoring. Only one site — Belmont, in the Maniototo, the glasswort refuge — is covenanted so far. But a management agreement for a site in the Upper Clutha Valley (Pisa Flats), has just been negotiated between DoC and the landowner Tom Gilmore. The agreement will ensure the site is not irrigated or cultivated, and grazed only sparingly. At a third site, the Sutton Salt Lake near Middlemarch, the owners have put in fencing to keep stock out. "By and large, farmers are supportive of conservation measures," says Mr Patrick, "because the areas in question are small — the biggest would amount to only 10 hectares even with a buffer zone — and they are not significant agriculturally. "Farmers also know that sheep like to gnaw at salty outcrops, which is not good for them. It ruins their teeth and thus their productive capacity." DoC is negotiating with the owners of several sites about formal protection. In the case of two sites, at Galloway Station (Alexandra) and Patearoa in the Maniototo,

Mr Patrick recommends interpretive signs be erected to emphasise the biological and historical importance of salty areas in the Central Otago landscape. Both sites are alongside roadways. The Patearoa site contains healthy colonies of Lepidium sisymbrioides, Cotula maniototo and Carmichaelia monroi. Two other plants typical of saline areas also occur here — Lepidium kirkii and Apium filiforme. Altogether, Mr Patrick has identified eight sites worthy of protection, with an additional two identified by the PNA scheme in the Upper Clutha that have salty soils but no native halophytes. As far as natural and conservation values go overall, however, all of these places are clearly worth their salt! #& Reference: Patrick, B.H. Lepitodptera of salt-pans of Central Otago. Department of Conservation, Dunedin. 1989.