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High altitude areas have a harsh climate, with low soil temperatures (< 5 C), exposure to winds, and a short growing season. These areas are wetter than adjacent areas down slope. Rainfall is especially high near to the Main Divide. These areas are characterised by podzolised, alpine and high country yellow brown earth which are all very strongly to excessively leached.

Soil acidity and low soil temperatures result in very slow plant growth. The high development and maintenance cost of correcting soil deficiencies has resulted in these areas not being economic to improve. Plant communities at high altitudes are therefore usually dominated by native species, with few weed or pastorally important species present.

Why tussock grasslands are here Chionochloa tussock grasslands would have occurred at high altitudes in prehuman times, and continue to do so. They naturally occur at high altitudes because, despite moist conditions, the lack of adequate summer growing temperatures prevent the growth of tall woody plants.

Since European settlement these grasslands have, relative to grasslands at lower altitudes, escaped major modification. On the western ranges, feral animals have been the main cause of any modification, On the drier ranges to the east of the Main Divide, grasslands have been modified as a result of mainly stock grazing and burning activities during the last 150 years of pastoral activity.

A reduction or cessation of grazing in these areas tends to encourage recovery to a vegetation community dominated by native species.

References:

Connor, H.E. 1964: Tussock grassland communities in the middle Rakaia valley, Canterbury, New Zealand. NZ J Botany 3: 261-276.

Floate, M.J.S. Ed. 1992:Guide to tussock grassland farming. Chapters 2 & 3 AgResearch, Mosgiel, Invermay.

Wardle, P. 1991: Vegetation of New Zealand. Cambridge Press.