The origin of the indigenous grasslands of southeastern South Island in relation to pre-human woody ecosystems

Immediately before human settlement, dense tall podocarp- angiosperm forest dominated the moist Southland and southern coastal Otago districts. Open, discontinuous podocarp-angiosperm forest bordered the central Otago dry interior, extending along the north Otago coast. Grassland was mostly patchy within these woody ecosystems, occurring on limited areas of droughty or low-nutrient soils and wetlands, or temporarily after infrequent fire or other disturbance. Podocarpus hallii, Phyllocladus alpinus and Halocarpus bidwillii, small-leaved and asterad shrubs formed low forest and shrub associations in the semi arid interior, with Nothofagus menziesii prominent in the upper montane-subalpine zone. Substantial grasslands were confined to the alpine zone and dry terraces in intermontane basins. The arrival of the first Maori settlers at c. 800 BP led immediately to widespread burning and near-elimination of the fire-sensitive woody vegetation from all but the wettest districts. Non-Chionochloa grasses (probably species of Poa, Elymus and Festuca) and, in particular, bracken were the first to spread after fire; later, with continued fire, the more slowly spreading Chionochloa tussock grasslands became common. A unique suite of dryland woody ecosystems has thus been replaced with fire-induced grasslands. Recreation of the pre-human vegetation cover from the surviving small remnants is problematical because of the anomalous fire-sensitivity of the indigenous drought-tolerant flora. In the current historically unprecedented fire-prone environment, perhaps the best that can be hoped for is preservation of the status quo.