The impact of human settlement on vegetation and soil stability in Hawke's Bay, New Zealand.

Widespread destruction of lowland podocarp/hardwood forests in Hawke's Bay followed permanent Maori settlement of the region. Forests cleared by fires were rapidly replaced with a bracken fern-scrubland which remained the predominant vegetation until European settlers cleared it away for pasture production in the late 1870s. Deforestation began about 500 calendar years B.P., but proceeded faster in the drier lowlands than in the wetter hill country. When the catchments were covered with either forest or fern-scrubland, soil erosion was minimal because the soil structure was maintained by the network of roots and protected from raindrop impact by a dense canopy. The main effect of storms before European settlement was to transport pulses of mostly riverbank sediment into the lakes. However, after European settlement, soil erosion increased markedly. Removal of soil stabilising vegetation and its replacement with pasture has left soft-rock hill country soils vulnerable to erosion and landslides.