Ecotypic Differentiation in Otago Populations of Narrowleaved Snow Tussock,Chionochloa rigida

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Abstract
The transplanting of segments of mature tussocks reciprocally between four field sites and also to a garden in a milder forest climate has shown that an interplay of genetic and environmental differences determines most of the variation between populations. Some of the genetically controlled morphological differences appear to have no survival value and are probably the result of correlated responses to the selective effect of the environment on the genetic system controlling growth. Genctic variation that is adaptive is displayed in the response to temperature of floral induction, and in the adjustment of flowering time and growth periods. It appears that some altitudinal variation within the species is ccoclinal, but the results based on only four populations suggest the presence of a distinct high-altitude ecotype of short tussocks above about 1,500 m. Populations arc variable with potential for further adjustment, but this must inevitably be slow because of longevity of tussocks, infrequent flowering, and self-fertility. Witn the possible exception of tussocks occupying recently deforested sites below about 1,000 m, the populations appear to be in equilibrium with the prevailing environment and do not suggest a relic species in process of extinction. The planting of lower-altitude tussocks to high altitudes, within the potential range of the specics, is recommended as a means of providing an effective plant cover on depleted sites.