Disturbance of varying scales is considered a dominating influence on the pattern, species composition and structure of New Zealand's montane and subalpine forests. The role of disturbance in forest development is discussed for forests dominated by beech species and mixtures of conifer and hardwood species along a gradient of increasing forest complexity. In pure mountain beech (Nothofagus solandri var. cliffortioides) forest, snowbreak and windthrow can lead to continuing mortality resulting from a buildup of pests and diseases. Mostly, it is the larger (older) trees that die. Because mountain beech regenerates abundantly on most sites after this type of disturbance, the dominant canopy species is maintained. In conifer-broadleaf hardwood forests of central Westland, canopy gaps (e.g., windthrow) can result in all canopy species regenerating. Landslides can lead to the development of even-aged stands dominated by the hardwoods southern rata (Metrosideros umbellata), kamahi (Weinmannia racemosa) and Quintinia acutifolia. However, where extensive synchronous canopy mortality occurs, kamahi and Quintinia acutifolia are more successful at regenerating than southern rata. In these mixed forests disturbance events can lead to replacement and displacement of canopy species in the short term. As the complexity of forest increases it is more difficult to isolate the role of disturbance in forest development from chance occurrences and autogenic processes.