A history of Kaiparoro clearing and the limits of Nothofagus in the northern Tararua Range, New Zealand

Abstract

Kaiparoro clearing is a 40 ha enclave of tussock grassland within forest, straddling a rounded peneplain remnant in the northern Tararua Range. The grassland occurs at an unusually low altitude compared with other North Island red tussock grasslands. Charcoal and pollen from a peat bog suggests that fire created the clearing and helped maintain open vegetation throughout its 3500+ year history. There appear to be no edaphic constraints on forest occupation of most of the site. Before the clearing was created, tussock grasses were probably confined to small riparian peat bogs within low forest on the peneplain surface. Rates of shrub invasion of the tussock clearing by Dracophyllum longifolium, Leptospermum scoparium, and Olearia colensoi are slow. A fire return-period of <400 years would be sufficient to perpetuate the open or non-forest vegetation. Kaiparoro coincides with the modern-day distributional limits of Nothofagus in the northern Tararua Range. The pollen record indicates that Nothofagus has had a delayed population growth there in the Holocene relative to the main population centre further south. Similar trends for Nothofagus at other provincial limits in its distribution are evident elsewhere in New Zealand. Pollen results from Kaiparoro and similar sites adjacent to Nothofagus boundaries, suggest that Nothofagus is non-competitive under humid, mild, low-insolation climates.

Keywords:

• Tararua Range
• palynology
• pollen analysis
• late Holocene
• peat bog
• fire
• paleoclimate
• Nothofagus
• beech