Late Holocene development of two wetlands in the Te Paki region, far northern New Zealand

Abstract

The history of two wetlands in far northern New Zealand is examined from stratigraphic and palynological evidence. Although both the Te Werahi and Ponaki wetlands appear superficiallysimilar (both are dominated by raupo, Typha orientalis, and both are barriered by unvegetated coastal sands), radiocarbon dates show that they are of very different ages. The Te Werahi wetland shows organic sedimentation covering at least the last 3,700 years. This suggests it originated at the time that sea-level reached its present position around 6,500 years B.P. A sharp rise in the abundance of charcoal particles in sediments from the Te Werahi wetland indicates an increase in fire frequency between 2,620 and 2,150 years B.P. A phase of forest reduction, and destabilization of coastal sands, may date to this period. The Ponaki wetland has developed within the last 200–300 years. We argue that fire removed the vegetation and led to erosion of catchment soils and destabilization of coastal sands. Blocking of the stream outlet by a sand barrier probably accounts for subsequent wetland development or expansion. Pollen and sediment data support these conclusions.

Key Words:

• pollen analysis
• wetlands
• fire history
• Te Werahi
• Ponaki
• forest clearance
• erosion