ECOLOGY OF DRACOPHYLLUM-SUBULATUM-DOMINANT HEATHLAND ON FROST FLATS AT RANGITAIKI AND NORTH PUREORA, CENTRAL NORTH ISLAND, NEW-ZEALAND

The structure, composition, and dynamics of heathland dominated by Dracophyllum subulatum (monoao) on “frost flats” (plateaus and shallow basins supporting low vegetation and subject to year-round frosts) at proposed Te Papa Ecological Area, Rangitaiki and Waipapa Ecological Area, Pureora, were investigated. Systematic sampling and subsequent classification identified five frost flat and related communities at Rangitaiki, the three minor ones apparently occupying moister sites of varying drainage and fertility; one frost flat and one related community had previously been identified at Pureora. The floristic affinities of frost flat heathland lie with the largely fire-induced tussock grasslands of eastern South Island; most of the ubiquitous species have wide ecological amplitudes and several of them are important early colonisers elsewhere in New Zealand. Mean annual diameter growth rates of monoao in the major communities at both localities ranged from 0.5 to 1.2mm yr−1; mean annual height growth rates ranged from 1.8 to 8.9 cm yr−1. Ageing of monoao indicated regeneration waves beginning after disturbance. i.e., fire. with progressive invasion occurring over many decades. Monoao dominance appears to have been maintained by periodic fire. With only feeble replacement in the absence of fire, D. subulatum is likely to be largely superseded by lichens (especially Cladia retipora) and mosses (Racomitrium lanuginosum) at Rangitaiki, where frosts are too severe for common early successional forest trees and shrubs, and where potentially colonising cold-hardy shrubs have been very reduced by a long fire history and may be excluded by very infertile soils. Reversion to high forest via early successional forest trees and shrubs is predicted on most sites at Pureora. The persistence of frost flat communities at Rangitaiki is being jeopardised by invasive weeds, mainly Pinus contorta and possibly Hieracium pilosella. © 1990 Taylor & Francis Group, LLC.