The distribution of plants in relation to pH and salinity on inland saline/alkaline soils in Central Otago, New Zealand

The distribution of plant species with respect to soil pH and conductivity was determined at two sites in Central Otago. About 20 species, only eight of them native, were recorded on soils of moderate or greater salinity (conductivity >800 mu S/cm) and pH > 7.0 at these sites, but a further four native species occur in similar habitat elsewhere in Central Otago. Species formed four ecological groups determined mainly by soil pH rather than conductivity, and by soil moisture: common native perennials of acid, non-saline, shallow, dry soils; common exotic pasture species of slightly acid, non-saline, deep, well-drained soils; herbaceous species of seasonally moist alkaline and saline soils; and herbaceous species of permanently moist or wet alkaline and saline soils. Two taxa formerly considered halophytic, Lepidium kirkii and L. sisymbrioides subsp. matau, were recorded growing only on non-saline soils, although soils supporting L. kirkii were slightly alkaline. The implications of these results for classification of native plants as halophytes are discussed.