Structure and Composition of the Abrupt Rain-Forest Boundary in the Herberton Highland, North Queensland

Abstract

Structural and floristic features of the rainforest-eucalypt forest boundary are described for two sites on the seasonally clouded eastern slopes of the Herberton Highland, north Queensland. Permanent sample plots, transects and canopy profiles were used to analyse variations across the narrow ecotone. The forest ecotone was found highly variable, spatially and temporally. Within rainforest, richness of woody species was maintained through to the closed forest edge. However, structural changes were more pronounced towards the boundary than were floristic variations and a fringe of immature rainforest varied in depth from 20-500 m.

In the open forest margin, tall trees of Eucalyptus grandls were restricted to a narrow zone between the rainforest edge and the broad expanse of medium height Eucalyptus intermedia. Within this transition, young rainforest trees and some shrubs were observed, during a 12-year interval, to be establishing beneath tall E. grandis, displacing fire-prone grasses in the process.

The distribution of old E. grandis within rainforest provides a record of recent boundary change. On evidence presented, the rainforest-eucalypt forest boundary is dynamic and parts of the rainforest are expanding due to favourable contemporary fire regimes.