Year

1995

Degree Name

Master of Science

Department

Department of Geology

Abstract

This is an analysis of the vegetation of the Ettrema and Northern Budawangs areas. These are the two core wilderness areas of the Morton National Park. The distinctive sandstone landscape of these two areas covers approximately one and one half thousand square kilometres. The vegetation communities, previously undocumented, are defined and then analysed in terms of their environmental interrelationships, both spatial and temporal.

The analysis began with the mapping and classification of plant communities. They were classified differently according to vegetation formation. Heathland and rainforest were subdivided on the basis of location and species composition. Eucalyptus forest was defined in terms of associations (sensu Beadle and Costin 1952) and gradients of change. The vegetation was mapped onto a series of topographic maps covering the area. These maps have been reproduced at a reduced scale in this thesis (Figs 3.3 -3.12). A full-scale set of 9 1:25,000 map sheets covering the area are lodged in the map library in the Geography Department at Wollongong University. Mapped vegetation units often equate with "land systems" (sensu Keith & Benson 1988), containing the classified communities in short spatial sequence.

The defined communities were then described in terms of their place in the landscape. The majority of communities were found to occupy more than one habitat. This was interpreted as the vegetational response to the changing balance of basic plant growth factors. It was found that communities could be statistically grouped in relation to plant macronutrients, whereas the extent to which communities could be grouped statistically according to topography was found to be relatively low.

Temporal changes were examined from the three perspectives of (i) stability of Eucalyptus associations (ii) evolutionary significance of rare species (iii) relationships between vegetation distribution patterns and fire.

(i) It was found that co-occurring groups of eucalypts are frequently composed of species which can (theoretically) interbreed, since they occur in the same subgenera. It was hypothesised that taxonomic distances amongst co-occurring species is a reflection of the stability of these associations through time.

(ii) Rare plants make up about 7% of the species collected during the course of this survey. These were categorised into a number of morphological and distributional groups. Some are closely similar to related species, while others are more taxonomically isolated. Some are consistently distributed through a particular habitat, whilst others are erratically distributed. A third and large group are disjunctly distributed over their entire range. The possible significance of these morphological and distributional differences in evolutionary terms was considered. The conclusion was reached that some may be more recently evolved than others, with at least one, Eucalyptus dendromorpha, possibly showing an adaptational response to recent increased fire frequencies. Others, as indicated by their distribution, may well have diminished as a result of changes following the arrival of man on this continent. Support for these hypotheses was drawn from the literature on evolutionary theory, climatic change and plant evolution as deduced from the macro- and micro-fossil records.

(iii) Broad relationships were observed between the high frequency of fire, its most usual direction of travel, and the pattern of distribution of fire-sensitive vegetation. Firesensitive vegetation was found to be in the least fire-prone locations. Eucalypts in the Ash Group are often killed outright by fire and are less likely to regenerate from lignotubers by means of epicormic sprouting. The representation of this group in the area is high, compared to its representation in the State as a whole. Evidence that some species may be rare, or their rarity may have been accentuated, as a result of fire, comes from the chance observation of erratic distribution of rare species in different habitats.

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