A late Holocene history of natural disturbance in lowland podocarp/hardwood forest, Hawke's Bay, New Zealand

Abstract

Palaeoecological investigations of sediment cores from two lake basins in the Tutira and Putere districts of Hawke's Bay demonstrate the impact of volcanic activity, fires, and storms on the vegetation and soil stability before human settlement and deforestation. A “disturbance curve” derived from the classification and ordination of pollen records, and correlated with charcoal and sediment records, illustrates relative forest disturbance over time. Before anthropogenic forest clearance in Hawke's Bay, forest composition fluctuated frequently as a result of disturbance from fires, droughts, and a major volcanic eruption. Each natural disturbance, indicated by short-term increases of seral taxa, was followed by complete forest redevelopment. Cyclonic storms were not a major cause of disturbance to lowland podocarp/hardwood forests in the region, nor to the bracken-scrubland vegetation that replaced the forest after clearance. However, storms scoured and rapidly transported riverbank sediments into the lake basins. Compared with the preceding natural disturbances, deforestation by early Maori settlers represents a type and magnitude of disturbance previously unrecorded in the cores.

Keywords:

• charcoal
• disturbance
• erosion
• fire
• lake sediment
• pollen
• Taupo Tephra