Effects of Management Practices on Narrow-leaved Snow Tussock,Chionochloa rigida

Abstract

Spring burning initiates physiological changes which persist for several seasons. During the first two seasons, growth of surviving tillers exceeds that in unburnt plants, but rates then decline for several seasons to values well below those of normal tussocks. This decline is preceded by prolific flowering which invariably occurs about 15 months after a fire. Stimulation of growth by reburning increases with the interval between fires. The physiological induction of flowering after fire occurs during the long days of summer and is attributed to increased temperatures in the blackened tussock crowns. Although morphological initiation usually occurs in autumn, the flowers do not emerge until the following summer so that there is more than one year's delay in the visible flowering response to spring fires. The delay is even longer in plants burnt during autumn. Doth vegetative and floral development arc earlier in recently burnt tussocks than in unburnt plants, but inflorescence height, floret size, and seed weight and viability all tend to be less. Nevertheless, total production of viable seed is greater in tussocks responding to burning, even in a year of general flowering. But the subsequent reduction in vigour may prevent the burnt plants from responding to an inductive environment in subsequent seasons. Any treatment which removes the bulk of leaf material (especially burning) initially Increases the rate of leaf extension and tillering and in addition promotes flowering. 1 towever, tussocks defoliated during autumn usually suffer a great loss of tillers. The adaptations of the species to fire are seriously counteracted by grazing, especially In the immediate f>ost-(irc period. Accordingly, much of the deterioration of snow-tussock grassland since European settlement can De ascribed to the combination of fire with unrestricted grazing rather than to fire alone.