The species Nothofagus solandri, within which two subspecific taxa are recognised, i.e. Nothofagus solandri var. solandri and Nothofagus solandri var. cliffortioides (for descriptions see below), occupies a wide geographical and ecological range throughout much of New Zealand. It is often the only tree species of any account throughout the headwaters of many of New Zealand's larger rivers, especially those which have their origins on the eastern side of the Main Divide in the South Island and in the central mountain ranges of the North Island. For this reason the species is one of our most important protection forest trees and the forests which it forms must be kept in a healthy regenerating condition in order that they effectively act as a barrier to excessive soil erosion and minimise fluctuations in water yield. To fulfill these requirements and thus to aid in the management of these forests, some knowledge of the ecological behaviour, the life history, and variations in the life history of Nothofagus solandri is necessary. The aim of this thesis is to investigate the life history and ecological behaviour of Nothofagus solandri, to relate variations in the life history to habitat and thus to attempt to explain the present geographic and ecological distribution of the species. During the course of this study many of the forests of which Nothofagus solandri is a component were visited, but detailed experimental work was mainly confined to the Craigieburn Range and Mt Thomas in North Canterbury and the Kaweka Range in the Central North Island.