Effects of Burning and Grazing on Sustainable Utilization of Upland Snow Tussock (Chionochloa spp) Rangelands for Pastoralism in South Island, New Zealand

Abstract

The upland (800-2000 m) snow tussock (Chionochloa spp.) rangelands of South Island, New Zealand have a long history of burning that pre-dates human occupation during the last millennium. Their present extent in part reflects their ability to displace a range of woody vegetation, including forest, through tolerance of periodic fne. Research has confirmed the general tolerance of these grasslands to fire, though recovery of some features (e.g. biomass and flowering potential) may take more than 14 years. Mammalian grazing, by contrast, is a recent phenomenon, associated with European settlement and pastoralism over the last 150 years, on these mostly Crown (i.e. public-owned) lands. Such grazing, particularly when combined with regular burning, has usually resulted in prolonged reductions in tussock biomass, vigour and stability, as well as in the control and yield of water, potentially the most valuable product for humans from the upland grasslands. Fire promotes vegetative growth, flowering and seed germination within 2 years of burning. It also increases the palatability of these long-lived dominant grasses which are vulnerable to severe grazing by introduced ruminants, especially in the immediate post-fire recovery period when nutrients are reallocated from roots to leaf tissue. Management constraints, particularly restriction of grazing during the post-fie recovery period, have been inadequate to prevent continued degradation of the grasslands through weakening or displacement of the dominant tussock grass cover and a consequent loss of stability in many areas. Under pastoralism, the productive potential of the grasslands, together with their water, soil and nature conservation values have generally declined. Existing pastoral practices in many areas clearly represent non-sustainable utilisation of the rangelands for pastoralism. Recovery will be difficult and costly, both economically and socially. Some representative areas have been formally reserved and are being monitored to serve as baseline references.