Hummock Grasslands Research Articles

Pattern and Change in an Acacia aneura Shrubland and Triodia Hummock Grassland Mosaic on Rolling Hills in Central Australia

The environmental correlates of a mosaic of Acacia aneura F.Muell. ex Benth. shrublands and Triodia hummock grasslands on rolling conglomerate hills in central Australia were explored by indirect gradient analysis. A non-metric multidimension scaling ordination, based on the presence or absence of plant species, clearly separated the A. aneura shrubland from the Triodia hummock grassland; there were few intermediate quadrats. The A. aneura shrublands occurred on relatively deeper skeletal soils than the Triodia hummock grasslands. Unlike unidirection successional gradients from frequently burnt, treeless vegetation to very infrequently burnt forest vegetation, the ordination presented here is unusual because the quadrats with the greatest cover of A. aneura and Triodia occur on the poles, and quadrats from the most recently burnt vegetation and with the least cover of A. aneura and Triodia occur in the centre of the ordination. Interpretation of aerial photography taken in 1950 and 1987 showed that there has been no statistically significant change in the coverage of these two communities over that time period. Some quadrats that contained Triodia on the boundary of A. aneura shrublands had numerous charred A. aneura stumps which was interpreted as indicating some retreat of the shrublands. Experimental studies are required to determine the stability of the current pattern. Biogeographic evidence, however, shows that the spatial distribution of both communities has fluctuated at a continental scale through geological time.

Species composition related to spectral classification in an Australian spinifex hummock grassland

Abstract This paper demonstrates a methodology for relating objective vegetation classifications to spectral classifications in order to map variation in species composition within natural vegetation. Landsat MSS data was used to map spinifex-dominated vegetation units for an island conservation reserve and oil production field on the north-western shelf of Western Australia. A significant relationship was established between an agglomerative hierarchical classification of ground samples, characterized by percentage cover of plant species and physical cover components, and a similar classification of spectral means for sample pixels. Assignment of spectral means to mapping classes was guided by both ground and spectral sample clustering. The strong relationship between the spectral classification and vegetation groups meant that cover classes mapped on the basis of spectral properties could be characterized by quantitative ground data meaningful to vegetation ecology. The resultant groups were differentia...

The Distribution and Abundance of Kangaroos in relation to Environment in Western Australia

Red and western grey kangaroos were surveyed from the air in Western Australia during the winter of 1981. The area covered, 1 528 000 km2 or 61% of the State, excluded only the Kimberleys in the north and the Gibson and Great Sandy Deserts of the interior. Hence almost all kangaroo range within the State was surveyed, to provide an estimate of 980 000 reds and 436 000 greys. Densities were much lower than those of the eastern States. Red kangaroos were most abundant in mulga shrubland, chenopod shrubland and tussock grassland, and least abundant in hummock grassland. Densities were associated strongly with land-use categories, being high in areas used for extensive sheep grazing and low in vacant Crown Land and arable land. In contrast to reds the western grey kangaroos were confined to the south and west of the state, their distribution being related more directly to climate than to vegetation or land use. They live in the winter rainfall zone. We suggest that their restricted breeding season results in peak nutritional demands associated with lactation, and hence energy requirements, being synchronized with the spring flush of pasture following winter rains. Approximately 14% of the red kangaroo and 8% of the western grey kangaroo populations in Western Australia were harvested legally in 1981.

Desertification of rangelands in arid Australia

Desertification means a long term decline in biological productivity of drylands. The case of arid Australia gives an example of the relationship between society and natural environment. The proofs of desertification are numerous (vegetational and physical deteriorations) , especially in the low acacia Woodlands and in the tussock and hummock grasslands, under grazing pressure. Different measures to combat desertification are possible : limitation of stocking levels to match the safe yield of the pastures ; efforts to improve productivity ; limitation of rabbit numbers...