Part 3: The altitudinal gradient in forest composition, structure and regeneration

Abstract

Changes in forest composition, structure and regeneration associated with increasing altitude from the eastern shore line of Secretary Island to tree line (2,950 ft) are described from a series of plots on a south-east aspect slope. Total and relative density values are presented for trees, small-trees, shrubs, herbs and regeneration categories of beech and podocarp species along the altitudinal gradient. Values are also presented for total and relative dominance (basal area) of the tree and small-tree layers, for canopy height and for stem size distribution of the important tree species along the gradient. Gradients in composition, structure and relative importance of species in the four strata are associated with increasing altitude, but rather abrupt changes in the tree, small-tree and shrub strata occur near the 1,500 ft contour. On this basis a lowland mixed forest and an upland beech forest can be distinguished. Among the 69 species listed in the four strata there is little indication that any are closely interdependent in distribution. The extensive overlap of altitudinal ranges is consistent with the individualistic concept of plant distribution. Because of the great variation in Fiordland forests, application of these results from undisturbed forest to other forests within the Fiordland region, may be rather limited.