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Accueil du site → Doctorat → Australie → Vegetation of the Hammersley Ranges, North-West Australia : characteristics and comparisons

Curtin University of Technology (2000)

Vegetation of the Hammersley Ranges, North-West Australia : characteristics and comparisons

van Etten, Eddie J. B.

Titre : Vegetation of the Hammersley Ranges, North-West Australia : characteristics and comparisons

Auteur : van Etten, Eddie J. B.

Grade : Doctor of Philosophy Ph.D 2000

Université de soutenance : Curtin University of Technology.

Résumé partiel
This study has characterised in detail the vegetation of the central Hamersley Ranges, and has compared these characteristics to similar environments elsewhere. Specific objectives were to : derive a hierarchical vegetation classification based on floristics ; find and describe floristic gradients and identify environmental gradients to which they were correlated ; delineate and describe spatial patterns in the vegetation and use vegetation- environment models to map such patterns ; identify dominance and diversity features and patterns of the vegetation at a range of spatial scales, and relate such patterns to environmental variables ; and, use such information to generate hypotheses relating to the causes of variation in the vegetation characteristics. The Hamersley Ranges is a mountainous region located in north-west Australia, some 1000 kin north of Perth. It dominates the southern half of the Pilbara Bioregion 1 Fortescue Botanical Province. The Hamersley Ranges describes the series of mountain ranges, ridges and hills which rise above the Hamersley Plateau, as well as the escarpments around the edge of the Plateau. Topographic relief varies between 50 to 600 in ; and includes the highest mountains in the State of Western Australia. The surface geology of the ranges and other uplands is chiefly ironstones, laid down by deposition during Proterozoic times. Banded iron- formations are common with layers of chert, shales, dolomite and siltstone, as well as volcanic intrusions, between the iron-enriched layers. Archaean granite and gneiss dominate in the south. Soils forming on uplands are characteristically shallow and skeletal, with chemical characteristics reflecting the underlying bedrock. Extensive lowlands with deeper soils are found between ranges and around hills, and consist of : pediments with ironstone pavements at base of uplands ; alluvial fans and bajadas of mostly sorted alluvium below the pediments ; and, drainage basins, flats and/​or creeklines at the lowest points in the landscape. These landforms are common to arid, mountainous regions elsewhere. The climate of the region was examined in detail. Interpolation of rainfall records in and around the Ranges demonstrated that the annual yearly average is between 250 to 400 min, from southern to northern margins respectively. 50-60% of rain, on average, is received between January to March. Variability of annual rainfall is medium to high, with coefficients of variability between 35 to 45%. This variability was shown to be higher, using regression analysis and statistical tests, than that of desert regions with similar rainfall averages, although it was less than other regions of arid, northern Australia, and arid regions elsewhere within the tropics. The proposition that the region, and Australia in general, have relatively high variability in inter-annual rainfall was supported, suggesting rainfall of the Hamersley Ranges is erratic and unpredictable. Given the immense size of the region (some 60K kin’), a study area in the middle of the Ranges was chosen. It was representative of all the major landform and geological types, and was intermediate in terms of climate ranges given above. The study area was approximately 100 X 80 km in size (15% of region) and centred within Karijini National Park at 220 31* S, 118’ 25’ E. This study area was stratified by landform and geology, and 139 study sites were chosen within representative patches of stratified units. At each study site, a 20 X 25 m plot was marked into 20 evenly sized quadrats. Cover and abundance of each perennial species was estimated ; these figures were used in conjunction with frequency (of quadrats) to calculate importance values for each species. Slope, soil depth, stone cover and other topo-edaphic features were measured at each site, and topsoil Q-5 cm depth) collected for analysis of nutrients, pH, conductivity, texture and color. Location was measured using GPS and relative distance to top of nearest hill top.


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