New Zealand Journal of Botany abstracts

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THE ENVIRONMENT AND GROWTH RATE OF NARROW-LEAVED SNOW TUSSOCK, CHIONOCHLOA RIGIDA, IN OTAGO

A. F. Mark*

Botany Department, University of Otago, Dunedin

Abstract The wide altitudinal range in Otago of narrow-leaved snow tussock, which reflects a wide temperature tolerance, is accompanied by significant variations in several aspects of size, growth, and behaviour of the tussocks, as well as in the flora and vegetation of the communities which it dominates. These differences associated with increasing altitude are more pronounced on the Old Man Range in Central Otago than on Coronet Peak to the west or on Maungatua near the east coast. The reason for this is not clear, though there are differences in weather patterns which may be of importance. The decrease in temperature with altitude probably determines the upper altitudinal limit of the species, while soil moisture deficits may be important in determining the lower limit of snow tussock in competition with the more drought tolerant hard tussock, Fesluca novae-zelandiae. Measurements of leaf elongation of only the youngest exposed leaf in individual mature tillers provide a relatively quick, yet apparently reliable, method of assessing the vegetative vigour of a tussock. Methods involving measurement of leaf regrowth after clipping, even of a few tillers of the many hundreds in a tussock, are unsatisfactory in that this treatment appears to alter the normal growth patterns of the plants. Growth rates of mature tussocks vary directly with temperature, and are largely reflected in tussock height. The length of the growing season varies from five to eight months over the environmental range of the species.

(Received for publication 6 November 1964
N.Z. J. Bot. 3 : 73-103

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