Fire, succession and reserve management in a New Zealand snow tussock grassland

Abstract

The aftermath of fire was examined in a New Zealand grassland reserve, dominated by the tall tussock Chionochloa rigida. Deliberate fire has not previously been used in reserve management in New Zealand. Following an accidental fire in part of the reserve in autumn 1976, part of the remainder was deliberately burnt in the following spring for an experimental comparison. Vegetation changes were monitored until 1988. After both fires, the exotic grass Agrostis capillaris was abundant. Shoot frequency of Chionochloa rigida was low after fire due to the loss of the canopy, but generally increased. Twelve years after the fire, the vegetation was still different between areas of different burning history. In the unburnt area, the shrub Leptospermum scoparium was replacing Chionochloa. Species frequencies were used to classify the vegetation by Cluster Analysis. A transition matrix was calculated for the communities so derived, and a Markovian model used to predict future vegetation changes. Medium-term replacement of exotic grassland by native tussock grassland was predicted, with replacement by native Leptospermum scrub after several decades. Native forest species, some now present in small amounts, could eventually replace the Leptospermum. It is recommended that Chionochloa grassland at this altitude should be burnt every 15–40 years to maintain the community. Chionochloa rigida is expected to tolerate this regime. Burning would prevent loss of the tussock grassland by scrub invasion and consequential scrub fires. Such fires would probably result in the replacement of most native vegetation by aggressive exotic shrubs, or, if they were controlled, by exotic grassland.