|Mitchell Grass Downs|
|Flat, open, nearly featureless plains between Winton and Kynuna.|
Mitchell Grass Downs are rolling plains, mostly treeless, extending from central west Queensland into the Barkly Tableland in the Northern Territory. Over 70% of the region is in Queensland. This entry deals with the downs in Queensland. The map at the end of this sheet outlines the extent of the downs in Queensland and the Northern Territory
Population centres on the Mitchell Grass Downs in Queensland include Longreach, Winton, Barcaldine, Camooweal, Boulia, Blackall, Hughenden, Julia Creek, Tambo and Richmond. Tambo is near the south-eastern extremity of the downs.
Queensland's Mitchell Grass Downs are dominated by largely treeless plains. Most of the region features heavy, cracking, black or brown, clay soils resulting from swamp and other alluvial deposits in the geological past. The soils are thought to contribute to the lack of trees by breaking apart horizontal root systems when the clay contracts; tussock grasses have vertical root systems not as seriously affected by cracking. Mitchell grass, a tussock grass named after the explorer Sir Thomas Mitchell, grows as scattered tussocks, about 20 cm in diameter, up to half a metre high and with roots more than a metre deep, allowing access to deep soil moisture. Other grasses may grow between the tussocks. There are four species of Mitchell Grass - most nutritious are curly Mitchell (Astrebla lappacea) and hoop Mitchell (Astrebla elymoides), barley Mitchell (Astrebla pectinata) is next in order of nutrition with bull Mitchell (Astrebla squarrosa) least nutritious. All are long-lived (up to 30 years); the grasses are generally resilient to grazing, drought and fires due to their extensive root system.
|Open woodland around headwaters of the Diamantina River from Cawnpore Lookout.|
|The Mitchell Grass Downs is the largest grassy ecosystem in Australia. The cracking soil supports distinctive fauna of reptiles, grassland birds and small marsupials adapted to the region's seasonality and variability in annual rainfall. The above-ground environment offers little shelter so there is a limited number of vertebrate species and few tree-dwelling birds; many animals use the cracks and deep fissures for shelter. Small carnivorous marsupials suit this environment.Very high densities of specialized skinks and snakes also find refuge in this fissured environment. When the annual rains come the fissures close and much of the landscape becomes waterlogged, encouraging the emergence of vast numbers of burrowing frogs.|
|Mitchell Grass Downs - page 2|
Undulating plains of the Mitchell Grass Downs are commonly devoid of major tree cover but there is open coolibah woodland on the lower-lying plains and along periodically flooded watercourses. In the east/south east, between Winton and Blackall, the Mitchell grassland has a light covering of trees including gidgee and coolibah with emu-bush along watercourses. Around Blackall the gidgee shrublands were cleared in the 1960s and 70s and buffel grass planted; this area is highly productive.
Rainfall on the Queensland Downs is very unreliable and wet years alternate with dry. Mean rainfall is less than 300 millimetres a year in the west (263 millimetres at Boulia), increasing towards the east and south (476 millimetres at Richmond, 412 millimetres at Winton and 526 millimetres at Tambo). Most rain falls between December and March. Driest months are usually July or August.
Summer daytime temperatures are hot with temperature increasing to the north and west of the Downs (i.e. towards Richmond and Boulia). Winter daytime temperatures are milder. Mean temperatures at Tambo range from 20°C - 35°C in January to 4°C - 21°C in July. At Richmond mean temperatures range from 23°C - 37°C in January to 9°C - 26°C in July. Boulia in the west records mean temperatures of 24°C - 39°C in January and 7°C - 23°C in July.
The Diamantina and Coopers Creek both flow into the Channel Country where they disappear into a maze of braided streams and terminal wetlands. West of the Diamantina system, in a southerly flowing drainage system, the Georgina River and tributaries drains part of the Barkly Tableland (in the Northern Territory) and the higher country around Mt Isa as well as draining the western part of the Mitchell Grass Downs in Queensland; the Georgina River disappears into the Simpson Desert in the south.
In the Winton-Boulia area, mesas topped by resistant duricrusts stand above the main grass downs. The hard duricrust layer protected underlying clays from erosion while softer surrounding terrain eroded leaving the mesa formations with flat tops and sloping sides; their red, yellow and orange colouring is distinctive. The mesa country is locally known as "Jump-Up Country"; it is vegetated by stands of lancewood and low eucalypt communities with a spinifex groundcover. This country contrasts sharply with adjacent cracking clay and Mitchell Grass.
Invading woody shrubs, such as prickly acacia (Acacia nilotica), tolerate the cracking clay and, without competition from other trees, have become aggressive invaders; prickly acacia is now a serious problem in the Queensland part of the Mitchell Grass Downs. This woody weed forms extensive thickets which hinder movement of stock and access to water and make mustering more difficult; it also competes successfully with native vegetation for light and water. The plant was introduced in the 1900s to provide shade and food for stock; seeds were deliberately and widely spread by pastoralists. The plant did not become a problem until production shifted from sheep to cattle. While sheep digest and destroy most prickly acacia seeds consumed, the seeds pass through cattle still alive so cattle spread the weed instead of controlling it.
Prickly acacia now covers 7 million hectares, 500,000 of which cannot be used for grazing as a result. The economic and ecological costs of this invasion have been high, with recent estimates that $5 million is lost per year in productivity, and a further $4 million spent on control. On very heavily infested areas, such as the headwaters of the Barcoo-Thomson system, reclamation costs are higher than the productive value of the land. In July 1999 five 'islands' of core prickly acacia areas were defined in central west Queensland stretching from Barcaldine north to Hughenden and west to Winton and Julia Creek. Eradicating prickly acacia in these areas is impractical or not economically feasible and effort is concentrated on research into biological control agents. Outside these areas the weed is eradicated.
Mimosa bush, another prickly shrub, is not officially classified as a weed but can spread over large areas of grassland if not controlled.
In the longer term, the presence of large woody weeds introduces a significant change in vegetation structure likely to result in substantial changes in both fauna and flora.
|Mitchell Grass Downs - page 3|
In the past 500 million years the area has been covered on three occasions by vast seas. Ocean covering the region about 100 million years ago left many fossils, some displayed in several townships. The more common fossils are of marine origin but there are fossils of land dwelling animals on display as well.
Most of the Queensland Mitchell Grass Downs is devoted to pastoral leasehold. The potential of the region was recognised by William Landsborough and Nat Buchanan in 1860 and in 1863 a pastoral lease of 2,000 square miles, named "Bowen Downs" was granted and stocked with 350,000 sheep and 35,000 cattle. In 1887 a large part of this original lease was resumed by the government and blocks of 40,000 acres were thrown open for selection; descendents of many of the original selectors are still in the area. The area remained a stronghold of the wool industry until the decline in the 1950s and 1960s and the region is now devoted mainly to cattle with some sheep still grazed. A main factor contributing to the change to cattle has been that sheep farming requires more labour than running cattle and the resources boom has attracted many workers away from the industry leaving a serious shortage. Much of the region depends on the underlying Great Artesian Basin for water.
Several main highways serve, or cross, the Queensland Mitchell Grass Downs. From the south, the Landsborough Highway (also named the Matilda Tourist Way) from Charleville and Augathella crosses a watershed divide leaving the Warrego River catchment (part of the Murray-Darling Basin extending south to Victoria) and enters the Barcoo catchment in the Lake Eyre Basin shortly before Tambo near the south-east extremity of the Mitchell Downs. The treeless plains are in evidence before Tambo and so, unfortunately, are woody weeds spreading over the grassland. After Tambo the road runs north-west through Blackall to Barcaldine where the Landsborough Highway joins the Capricorn Highway from Rockhampton then turns west towards Longreach. Between Barcaldine and Longreach extensive stands of gidgee trees grow near the road.
Longreach (population 4,500) is the major population centre on the Mitchell Grass Downs. This is a service centre for the surrounding pastoral leases but has also developed a number of significant tourist attractions. The Qantas Founders Outback Musuem, with a Boeing 747 and Boeing 707 parked outside, is impossible to miss when approaching Longreach from the south. The Australian Stockman's Hall of Fame nearby includes a wide variety of displays and presentations portraying the stockman's life as well as many other aspects of the cattle industry. There are several other interesting places to visit in Longreach.
|Left. The Stockman's Hall of Fame at Longreach. Right. Kronosaurus Korner at Richmond displays local fossils.|
|From Longreach the Landsborough Highway / Matilda Way heads north west to Winton. The terrain remains flat while the gidgee common near Barcaldine thins out and flat-topped rocky outcrops become more common, some quite close to the road, others distant. These are the residue of a former plain which has been eroded away except where harder rock protected underlying clay from erosion. Approaching Winton the red mesa formations are in distant view off to the left (west), these include Bladenburg National Park established to preserve the special environment which evolved on these mesas. Winton is a service town hosting the Waltzing Matilda Centre commemorating Australia's national song supposedly written at Winton.|
|Mitchell Grass Downs - page 4|
|Mesa country viewed across woody weed infested area west of the Landsborough Highway south of Winton.|
From Winton lesser, but still bitumen, roads go west to Boulia and north-east to Hughenden. These minor roads, many
classified as Developmental Roads, were built primarily for trucks carrying stock which has priority on the mainly single lane
road. The bitumen surface is often quite good but mostly narrow, with occasional "Overtaking Opportunities" where a second
lane has been added for a short distance.
The main road, the Landsborough Highway, continues north west from Winton to the small villages of Kynuna and McKinlay. The duricrust topped mesa country does not extend that far north so both Kynuna and McKinley are surrounded by gently rolling or flat grassland. The Downs end north of McKinley; entering an area of hundreds of termite nests about 80 kilometres before Cloncurry was as good a sign as any of the end of the Downs. Just before reaching Cloncurry (outside the Mitchell Grass Downs) the Landsborough Highway meets the Flinders Highway from Townsville/Charters Towers.
Main bitumen roads on the Downs are generally of reasonable quality although sometimes sections are a bit rougher than expected on major rural roads. Care needs to be taken approaching birds feeding on road-kill carcasses. Common scavenging birds (kites and ravens) can fly clear of an oncoming vehicle without being hit. Eagles, which are increasingly resorting to road-kill for food, act more possessively and are reluctant to give up their find to get away from a vehicle bearing down on them; they are likely to wait too long before taking off. Unfortunately, these heavy birds do not gain height quickly and the combination of late taking off and slow rate of climb too often proves fatal for them and dangerously messy for motor vehicles. Fuel is readily available in each of the population centres; when travelling the Landsborough or Flinders highways vehicles using petrol or diesel fuel should not require special planning for daytime fuelling. Preparation for travels along minor roads should include fuel planning. Longreach has an extensive shopping centre and other towns have useful shops. Fresh water is available in townships but many rely on bore water which may be quite sulfurous. The strong smelling/tasting water is safe to use but a cup of tea made with sulfur bore water tastes unusual.
¶ Australian Natural Resources Atlas - Rangelands site.
¶ Encyclopedia of earth at http://www.eoearth.org
¶ Climate details at OzThunder at http://home.primus.com.au/ozthunder/oz/front.html and the Bureau of Meteorology at http://www.bom.gov.au/climate
¶ Savanna Explorer - North Australia information resource - at http://www.savanna.org.au - the map is based on this site.