GROWTH AND VEGETATION HISTORY OF ALPINE MIRES ON THE OLD-MAN-RANGE, CENTRAL OTAGO, NEW-ZEALAND

Alpine mires are widespread on the flat-topped mountains of Central Ot ago, the driest and most continental region in New Zealand. Feat profi les, pollen analyses, and radiocarbon dates are presented for several mires from the Old Man Range as part of a study of the environmental h istory of this region. Precipitation in the early Holocene may have be en up to 30% less than that of the present, and peat accumulation was restricted to topogenous mires. Alpine ombrogenous bogs began growth a t ca. 7500 BP. At the same time, forest and tall scrub spread in the a djacent lowlands in response to increasing rainfall, replacing grassla nd-shrublands. Feat accumulation was slow and episodic and declined to very low rates after 3000 BP, probably as a result of cooler winters and drier summers. Low levels of natural fire occurred throughout the Holocene. However, from 750 BP onwards, lowland forest and scrub was s everely reduced, subalpine shrubland declined, and snow tussock grassl and increased markedly as fires lit by Polynesian hunters swept the re gion. From A.D. 1850 onwards, European pastoralists introduced sheep a nd increased the burning of the uplands to improve grazing. Feat accum ulation increased in topogenous mires after burning and grazing of the alpine grassland, possibly because of accelerated runoff and nutrient input.