Western arid region land use study - Part 5

Abstract

This study focuses on nine million hectares of pastoral lands in western Queensland, centred on Longreach.
The area receives less than 500 mm average rainfall per annum, with over 70% falling in summer (October to March). Rainfall decreases in the south-western portion, which receives 25% less per annum. Rainfall is very variable with periods of drought frequently extending beyond one year. Evaporation rates exceed precipitation. Temperatures range from 35.5°C (mean summer maximum) to 10.1°C (mean winter minimum) for Longreach.
The area is part of the Great Artesian Basin comprising portions of the Eromanga Basin which have formed over basement rocks which are predominantly low grade metamorphics of the Ordovician to Devonian ages. Uplift followed by shallow marine deposition, has formed a series of geologic layers in these basins. The area is drained by the Thomson River and its tributaries.
A survey was carried out to provide an inventory of the land resources of the area: soils, vegetation, land systems and current land use. Soil and vegetation categories were mapped at a scale of 1:500 000 and 38 land systems were described. Industry in the area is presently based on the grazing of natural pastures by sheep and/or cattle.
The area comprises three distinct regions and major differences are evident in productivity and land stability between these regions.
The mulga lands in the south-west are unstable and the productivity of substantial areas has been reduced by erosion and the invasion of unpalatable shrubs. The upland regions are in a state of natural erosion and result in outwash sandplains. From a productivity viewpoint, these areas are marginally productive and subject to high runoff during times of high storm intensity.
The alluvial plains, alluvial woodlands, mitchell grass downs and gidgee lands are relatively stable, highly productive areas for the production of wool, mutton and beef.
On the basis of the resource inventory, there is concern for the long term future of the southwest portion of Warlus V. This portion is characterised by instability and decreasing productivity associated with land degradation. Recommendations on this and other, more regional, aspects were defined.