Pattern of natural regeneration of narrow-leaved snow tussock chionochloa rigida ssp. Rigida in central otago, new zealand

Abstract

Regeneration of Chionochloa rigida ssp. rigida (Poaceae) was investigated in two adjacent unburnt sites subjected to different levels of grazing by merino sheep over an 8 year period. The spatial pattern of establishment of immature plants within a 3 m radius of 100 isolated mature tussocks (basal diameter >20 cm) was recorded. Basal diameter, height, canopy width, slope, and aspect of the putative parents were noted, was was the size and position of the immature plants (basal diameter <10 cm). At the lower grazing intensity the number of immature plants increased with tussock size. Small tussocks had disproportionately few immature plants. The regeneration shadow was highly skewed, 72% of all immature plants occurring downhill and downwind from the tussock. Highest densities of recruits established between 0.5 m and 1.0 m from tussock centres. Few immature plants established within one diameter of the base of mature plants. Grazing affected regeneration by: (a) reducing overall recruitment (0.90 versus 4.0 immature plants per tussock); (b) reducing the proportion of seedlings in the smallest size class (20.0% versus 41.4% of seedlings with basal diameter <2 cm); (c) reducing mean seedling height (15.3 cm versus 23.0 cm); and (d) reducing the proportion of more distant immature plants. Regeneration was successful in the absence of fire and at low grazing intensity, probably <0.2 stock units ha-1yrl. However, recruitment was low under moderate grazing and uphill and upwind of mature tussocks. These factors need to be considered in the rehabilitation of narrow-leaved snow tussock grasslands in Central Otago. © 1993 Taylor & Francis Group, LLC.