Edaphic adaptation in species of Chionochloa

Abstract

Species of Chionochloa are tall tussock grasses which dominate the mountain vegetation in both islands of New Zealand. In the South Island they cover more than ten million acres of high country above about 600 metres and still persist in many localities at considerably lower altitudes. Snow-tussock grasslands dominated by C. rigida, C. macra, C. flavescens and C. pallens are widespread on mountain slopes, while red-tussock grasslands dominated by C. rubra are common in but not confined to damp or wet places on poorly-drained soils. Tall tussocks have a vital role to play in soil conservation and indirectly in flood control and also in water conservation for irrigation and to a lesser degree for hydro-electric power. They are also a primary source of food for sheep and cattle especially in the emergency of heavy falls of snow or during drought. The recreational value of tall tussock grasslands is increasing with population growth and increasing complexity of urban life. This thesis reports a further investigation into edaphic adaptation within the Chionochloas. The survey of populations in the field may disclose relationships between features of the habitat and characteristics of the plants which hint at mechanisms of adaptation. Measurements were therefore made of populations and soils of C. flavescens and C. macra from Porters Pass, and of C. flavescens, C. rubra and C. pallens from Mt Arthur Tableland. Transplant experiments enabled us to test the adaptation or pre-adaptation of populations to particular components of an environment, by keeping other factors constant. The aim of this experiment was to discern, in common climate, differential growth patterns and responses to soils among and within the three species, and to correlate such responses with the abundance of forms of phosphate in five soils which typically support two of the species in nature. Knowledge of the physiological variability within species, and between closely related species, is essential for a full understanding of the autecology of species, of their ecological amplitude and the nature of their distributional limits, as well as for a clearer understanding of the concepts of "indicator" species and "fidelity".