In South Island (New Zealand), large areas of narrow-leaved snow tussock Chionochloa rigida
grassland have developed in response to anthropogenic fires and concurrent native forest loss. Although human-induced, such grasslands have conservation value. At Flagstaff Hill (45°50'S, 170°27'E; 668 m) in Otago, an accidental fire burned 70 ha of tussock grassland in autumn (March) 1976. Subsequently 20 ha was deliberately burnt in spring (September) 1976 to assess the potential of burning management for C.rigida
grassland conservation. An earlier study on Flagstaff (one and nine years after these fires), suggested convergence in species cover and frequency between autumn- and spring-burnt sites (Allen & Partridge 1988; for our summary see: www.conservationevidence.com/ViewSummary.aspx?ID=12037
). Here, a longer-term (13-years post-burn) assessment on C.rigida
recovery is presented.
Five areas of tussock grassland (500-650 m altitude) were selected: three (at different altitudes) burnt in spring 1976, one burnt in autumn 1976, and one unburned for at least 25 years. In each area, a 20 x 20 m plot was randomly located within which the number of tussocks and basal area, canopy cover, and number of tillers were recorded in 10 (1m²) quadrats.
From each tussock, four tillers were selected at random, broken at the leaf-stem junction and the following measured for the longest leaf: total leaf length (sheath + lamina), green leaf length (sheath + green lamina) and sheath length. Above-ground biomass measurements were also made.
The spring-burnt areas generally had lower canopy cover, tiller density and above-ground biomass than the unburned area. The two higher elevation spring-burnt areas had significantly lower tiller weight and total leaf length than the other three areas. However, the green to total leaf length ratio was highest in the uppermost spring-burnt site. The only significant difference between the autumn-burnt and unburned area was that the autumn-burnt area had a greater sheath to total leaf length ratio.
These results suggest that the spring fire had a longer-term impact on tussock recovery than autumn burning. Thus the previous belief that spring fires are less damaging to C.rigida tussocks than autumn fires warrants further investigation.