The influence of aspect on the composition and structure of dry sclerophyll forest on Black Mountain, Canberra. ACT

Abstract

Observations in a number of stands of Eucalyptus macrorhyncha-E. rossii dry sclerophyll forest on the Southern Tablelands of New South wa!es had suggested that differences in botanical composition and structure were associated with differences in aspect. Quantitative studies were made in a relatively undisturbed forest on Black Mountain.

For assessment of the forest overstorey, permanent transects 10 ch by 1 ch were established on north- and south-facing slopes parallel to the ridge or valley axis. All stems of 4 in. diam. at breast height or more were identified and measured. Shrub and herbaceous strata were assessed on five north-facing and five south-facing slopes. A list of species, together with an estimate of cover for species occupying more than 1 % of the plot area, was recorded on 100 contiguous milacre plots along the mid-line of the permanent transects.

There were no significant differences between north and south slopes in respect of total number of stems or basal area of trees. In terms of both density and basal area, however, E. rossii is the dominant eucalypt on the warmer northerly aspects, while E. macrorhyncha is dominant on the cooler southerly aspects.

On the basis of the frequency data, three groups of shrubs can be recognized, viz. (1) species of high frequency on north aspects but relatively low frequency on south aspects; (2) species of similar frequency on both aspects; and (3) species which occur most commonly on south-facing slopes.

Of the two common grasses, Danthonia pallida occurs with equal frequency on both aspects, while Poa sp. is virtually absent on north-facing slopes but occurs with the same frequency as D. pallida on south aspects.

Though total cover of shrubs plus herbaceous species is similar on both aspects, shrubs characterize the understorey on north aspects, and grasses on south aspects.