Waikerikeri Terrace Flats
Outwash gravels of the penultimate glactiation form broad, very gently south-sloping terraces with regular wide, shallow, southward-draining channels. Waikerikeri stony sand soils- a moderately developed soil with shallow profile; Drybread group brown grey earth. Vegetation
The grassland is extensively grazed but otherwise agriculturally undeveloped. There are marked seasonal changes in the vegetation, and spatial variation that results in a mosaic of large patches dominated by different groups of 3 or 4 species. These patches are distinguished as the following vegetation types: 1. Tussock grassland:
Silver tussock provides 10-30% cover over areas varying in size from small patches of less than 100sq.m to entire interfluves of several hundred square metres. Fescue tussock and blue tussock are usually associated, with a cover generally less than a third that of silver tussock, but are rare where silver tussock are sparse. Sweet vernal is the main intertussock species, particularly prominent in summer, a time when haresfoot trefoil is also important. Small Pimelia aridula shrubs occur at low density, and are mainly confined to this vegetation type, and sweet brier is most common here with plants 0-5-1m tall at densities of 1-3 plants per 100sq.m. matagouri is present but is an insignificant component of the vegetation. 2. Harefoot trefoil herbfield.
May cover about 30% of areas of up to several hundred square metres of silty soils, where perennial grasses or shrubs are lacking. Scabweed can be prominent. About 20% of the ground is bare, and a mixture of lichen, small annual grasses and herbs provide the balance of cover. In winter, the lichen Chondropsis semiviridis covers up to 80% of the ground otherwise left bare by the departed annuals. 3. Danthonia- sweet vernal grassland:
An almost continuous turf in winter, dominated by Rytidosperma, and in summer, also sweet vernal, found in the floors of most drainage channels. 4. Thyme shrubland:
Thyme shrubs, mostly less than 0.4m tall, form a dense stand of up to 100 sq.m. in extent, mainly on the eastern rims of drainage channels. In winter the ground between the shrubs is largely bare, in summer harefoot trefoil and a few other herbs provide a sparser cover. Many species occur throughout all these vegetation types. Grasses include native Rytidosperma and blue wheat grass; the introduced annual silvery hair grass, downy brome and soft brome. Most herbs are exotic e.g. suckling clover, catsear, sheep’s sorrel, hawksbeard, white fuzzyweed, vipers bugloss, sheep’s burr, and St Johns wort. The most common native herbs are Geranium sessiliflorum and Carex breviculmis. Species list:
The terraces west of the lower Manuherikia River are habitat for the Alexandra chafer beetle Prodontria bicolorata as well as an undescribed species of weta. Both species have been recorded in or around the Waikerikeri terrace grasslands (B.Emerson unpub.). The diurnal moths Notoreas n.sp. and Eurythecta zelaea have been found too. Discussion
The vegetation of the part of the Waikerikeri terraces described here is closer to a natural state than that described for similar glacial outwash terrace landforms in any other part of the Central Otago Ecological Region. Elsewhere on the terraces of the lower Manuherikia Valley, tussock densities are negligible, and the vegetation is dominated by exotic grasses and weeds, or by fodder crops. No similar vegetation is protected in the remainder of the Maniototo Ecological District. The Cromwell chafer beetle reserve, with extremely depleted vegetation, is the only example of such vegetation-landform protected in Central Otago. A reserve on the Waikerikeri terrace, encompassing the representative vegetation and providing protected habitat for the chafer beetle, would be and important addition to the network of protected natural areas in Central Otago from both biological and landscape perspectives. Immediately north of Waikerikeri terraces, the grasslands surrounding MacArthur Road (G42 265 565) have an abundance of native species mixed in with the exotic sweet vernal sward. The physiognomic dominant is the short tussock Festuca novae-zelandiae, while some Poa cita is present also. This would appear to be the opposite of the nearby Waikerikeri terraces where P.cita is the commonest tussock. The shrubs Pimelia aridula and Melicytus alpinus are also common in the area. Other common native species at MacArthur Road site include Rytidosperma maculatum, R.clavatum, Elymus rectisetus, poa colensoi, Carex breviculmis, Geranium microphyllum and Vittadinia australis. Flushes running through the grassland hold water only seasonally and are dominated by a variety of Carex spp, and both native and exotic species of Juncus. Some bare, possibly salty sites have populations of spring-flowering Myosurus. The MacArthur Road area deserves further study to more fully describe its flora and fauna, as some of it could possibly make a worthwhile addition to the Waikerikeri Terrace Flats RAP. Information taken from the Maniototo Ecological District PNA Survey Report.