AbstractsGeography &GIS

Ecology of the forests of south western Australia in relation to climate and landforms

by Jaroslav J. Havel

Institution: Murdoch University
Year: 2000
Record ID: 1031923
Full text PDF: http://researchrepository.murdoch.edu.au/70/


This thesis sets out to test the hypothesis that the vegetational patterns in the forested region of south western Australia are primarily determined by the interaction of climate and landform. The region is an area of 4.25 million hectares subject to recent agreement between the Commonwealth of Australia and the state of Western Australia regarding long-term protection and management of forest (Regional Forest Agreement). The climate of the South Western forest region is warm temperate and summer dry, matching Koeppen's category Cs, usually described as mediterranean. The dominant geological features of South Western Australia are crystalline and sedimentary plateaus and coastal plains. They are subject to a complex process of weathering, denudation and re-deposition, which is the key determinant of landforms and soil patterns. Deep but infertile soils are prevalent. The dominant vegetation formation of the region is open forest, which reduces to woodland in the drier north and east and increases to tall open forest in the moister south. Floristically the vegetation is very rich, comprising over 3000 vascular plant species. The richness resides in the forest and woodland understorey and in the shrublands, heathlands and sedgelands of edaphically extreme sites. By comparison, the forest overstorey is very simple, only one or two species being often dominant over extensive areas. The validation of the hypothesis that climate and landforms determine the vegetation patterns in South Western Australia is carried out in the following stages: 1) review of past studies of vegetation patterns in relation to the underlying environmental factors, relating them to one another in terms of floristics, 2) conversion of landform and climate maps for the region into vegetation maps by means of toposequences, that is gradients of topography, soils and vegetation within individual landform/climate combinations, 3) production of two sets of vegetation maps, namely six maps of vegetation complexes (1:250,000) and one map of vegetation systems (1:500,000), 4) testing the predictive capability of the resulting maps by comparing the occurrences of individual species of trees, shrubs and herbs predicted by map legends, with their records in FloraBase, the geographic information system of the Western Australian Herbarium, and 5) using the outcomes of the above studies to assess the validity of the hypothesis. Because the above hypothesis is so broad, it will be considered under seven headings: a) nature of the vegetation patterns (continuum or discrete categories), b) regional effect of climate and local effect of landform, c) effect of landforms on soil depth, texture and fertility, d) joint effect of slope, soil depth and texture on water balance, e) interactive effect of landform and climate on vegetation patterns, f) response of individual species to climate and landform, and g) effect of other factors of environment, such as fire, on vegetation patterns. The subsidiary hypotheses are defined in Chapter 5. It is…