High-alpine environments and primary production on the Rock and Pillar Range, Central Otago, New Zealand

Abstract

Cushion and herbfield communities, characteristic of the Central Otago high-alpine zone, are subjected to severe environments : persistent strong winds, low air and soil temperatures with many freeze-thaw cycles during the 5-month growing season, and moist frost-active soils. Sites in herbfield experience somewhat higher temperatures and lighter winds, and have deeper soils with greater profile development and higher organic content than cushion sites. Compared with alpine communities of similar physiognomy from the Northern Hemisphere, the snow-free season is very long, about 6 months, and plants grow, at least intermittently, throughout much of this period. Annual net above-ground production of herbfield (208–255 g m⁻²) is about twice that of cushion vegetation (126 g m⁻²) where very high stem densities compensate for the extremely small production of individual stems. Annual productivity is somewhat higher than for many physiognomically similar communities overseas but the longer growing season reduces daily productivity and efficiency to more closely approximate overseas values. An unusually large proportion of the total standing crop is above ground, particularly in the cushion community, and turnover rates for above-ground biomass are rather slow (7.6 years in herbfield; 11.4–15.3 years in cushion).