Alpine Vegetation, Plant Distribution, Life Forms, and Environments in a Perhumid New Zealand Region: Oceanic and Tropical High Mountain Affinities

Abstract

Macro- and mesoscale patterns of the full altitudinal range (1200–2200 m) of alpine vegetation and vascular flora on Mount Armstrong, on New Zealand's perhumid Southern Alps, are deduced from 41 vegetation and soil samples. Multivariate analyses of quantitative data for 138 vascular plant taxa separated high-alpine from low-alpine communities between 1640 and 1800 m depending on local topography. Four high-alpine and seven low-alpine communities were differentiated. Vector fitting of 25 environmental variables to a sample ordination revealed 16 were statistically significant. Factors associated with topography (altitude, exposure, and slope) are the primary determinants of the macroscale patterns while soil, particularly those factors affected by processes associated with site stability, determine the mesoscale patterns of the alpine vegetation. Dominance of Hemicryptophytes and Chamaephytes across the alpine zone reveals a general consistency with alpine areas elsewhere. The tussock or caespitose form of Hemicryptophyte is the most common in New Zealand except near the upper limit of the high-alpine zone where cushion and mat forms dominate. Several large-leaved, mostly evergreen forbs (megaphyllous herbs) are a feature of the New Zealand low-alpine zone in perhumid regions. The overall pattern of alpine vegetation and associated life forms in oceanic New Zealand shows closer affinities with those occurring on perhumid tropical high mountains and other oceanic regions, particularly the subantarctic islands, than those of the temperate northern hemisphere continental mountains. The similarity between the moderate, extended but variable alpine growing season in New Zealand and the nonseasonal environments of tropical high mountains and subantarctic islands is suggested as the basis for this affinity. This contrasts with the much shorter but generally more favorable growing season and the extreme winters of temperate northern hemisphere continental mountains. Two data sets, one from Mount Armstrong and the other gathered from a wider geographic and altitudinal range, revealed curvilinear rather than linear relationships for both richness and altitudinal ranges of the vascular flora. Detailed information on altitudinal ranges and distribution of the alpine vegetation, vascular flora, life forms, and environments over the full range of the alpine zone on Mount Armstrong provides baseline records relevant to future assessments of probable effects of global climate changes.