An altitudinal transect in rain forest in the Barrington Tops area, New South Wales

Abstract

Abstract On the southern slopes of Barrington Tops, N.S.W., an exploratory study was made of altitudinal gradation between subantarctic or temperate rain forest (at higher elevations) and subtropical rain forest. The former is dominated by Nothofagus moorei while the latter has no clear dominants and is floristically and structurally more complex.To sample the ecotone, a single 800 m line containing thirty‐seven 200 m2 circular plots was placed on a S.S.W.‐facing slope between altitudes of 800 and 1040 m. The inclinations of the surfaces of individual plots ranged from 5° to 35°. Measurement and analysis were restricted to trees (including coppices), vines and tree ferns, with emphasis on density, basal area and importance values. Vertical extent of the ecotone is determined rather arbitrarily as being about 90 m. Floristically, the ecotone has elements both of a mosaic and of a gradual mix of species of the upper and lower rain forests. Its areal complexity is increased by the presence of small‐scale topographic features; the typical step‐and‐terrace sequence resulting from dissection of multiple basalt flows. There is a gradual dropping out of species of the subtropical rain forest upwards along the whole transect. The rate of drop‐out is greatest at the bases of any steep steps on the slope. Certain species, notably Doryphora sassafras, are shared by the two kinds of rain forest. In physiognomy too, there is further evidence for continuity: the size and density of vines as well as leaf sizes of trees and vines decrease gradually upwards. In terms of Webb's system of structural types of Australian rain forest there is sustained gradation from notophyll‐microphyll vinefern forest (at the bottom) to microphyll fern forest. There is strong evidence that Nothofagus moorei is not regenerating within most of the ecotone. Speculation is offered about ecotonal dynamics in terms of climatic change, fire frequency and the mode of reproduction of N. moorei.