Australian Natural Resources Atlas

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Rangelands - Overview

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Location map of Mitchell Grass Downs bioregionphotograph

Mitchell Grass Downs

Summary

ATSIC Boundaries

Catchment Basins

Statistical Local Areas

Introduction

The Mitchell Grass Downs bioregion forms a band of 335,100 sq. kms spanning across the central west of Queensland and Northern Territory. Over 70% of the bioregion lies within Queensland. Major towns in the region include Longreach, Hughenden, Blackall, Winton, Richmond, Julia Creek and Boulia in Queensland and Elliott in Northern Territory. The bioregion experiences a dry monsoonal climate merging to arid conditions to the south and south-west and sub-humid tropics along the north (Kerle, 1996).

Natural Environment

Climate

The climate is controlled largely by high pressure cells travelling east, except during the summer months when the north-west monsoons impact on the northern parts of the region. Rainfall across the region decreases from north to south and from east to west. The north receives 85% of rain from December to February. The south receives less than 70% of annual rain in summer. For further details see: www.savanna.ntu.edu.au/information/savannaexplorer.html.

Mean temperatures at Brunette Downs range from 24°C - 39°C in December and 10°C - 27°C in July. Mean temperatures at Tambo Post Office range from 19°C - 35°C in December and about 3.5°C - 21°C in July.

Climate averages are available for Tambo, Queensland:

www.bom.gov.au/climate/map/climate_avgs/a35.shtml and Brunette Downs, Northern Territory:

http://www.bom.gov.au/climate/map/climate_avgs/a14f.shtml.

For monthly rainfall and temperature graphs refer to Bureau of Meteorology website: www.bom.gov.au/climate/forms/map_forms/new_imagemaps/qld_name.html; and www.bom.gov.au/climate/forms/map_forms/new_imagemaps/nt_name.html.

For additional climate information the Queensland Department of Natural Resources ‘The Long Paddock’ at: www.dnr.qld.gov.au/longpdk provides seasonal variability information and the latest El Niño Southern Oscillation (ENSO) information. ‘Silo’ at: www.dnr.qld.gov.au/resourcenet/climate/#silo provides agro meteorological data, such as rainfall, temperature, radiation, climate outlook products. The Queensland Department of Natural Resources’ Patched Point Dataset and Data drill at: www.dnr.qld.gov.au/resourcenet/silo/index.html, provides information on climatic risk management in agriculture, pastoralism, water resources and natural resource management.

Landforms and hydrology

The entire area is dominated by largely treeless plains of Mitchell grasses with some occasional ridges, rivers and gorges. The region is generally gently undulating with the major geological units being the Dunmara/Barkly Basin in the north-west and the Georgina Basin in the south-east. From the end of the Proterozoic (545-2500 million years ago) period the area was covered on three occasions by vast, expanding seas. Wooded areas of boree (Acacia tephrina) or gidyea (Acacia cambagei) are common in the east/south east of the region.

The Mitchell Grass Downs extends over the watershed separating many of the northern and southern flow rivers in Queensland. Some of the rivers that flow north include the Flinders and William Rivers. The Barcoo, Thompson, Diamantina, Hamilton, Burke and Georgina Rivers flow south into the Channel Country bioregion, and may eventually flowing into the Lake Eyre Basin (Sattler & Williams, 1999, Connors, et. al., 1996).

For more detailed geological information and map refer to the Australian Geological Survey Organisation website: www.agso.gov.au/map/ and the Department of Mines and Energy, Queensland: www.dme.qld.gov.au/gsd/index.htm.

Soils

Most of the bioregion features heavy soils resulting from swamp and other alluvial deposition during the Tertiary period. Mitchell Grass Downs is characterised by cracking clay soils that are thought to contribute to the lack of native trees in the area and support distinctive fauna. Smaller areas of limestone with calcareous desert soils and lateritic plains with red earths and red sands are also present (Kerle, 1996, Mills 1980, Mills & Lee 1990 and Turner et al. 1978 and 1993).

For further information on soils refer to Sattler & Williams (1999) and the Digital Atlas of Australian Soils.

Vegetation

The bioregion is dominated by Mitchell grass (Astrebla spp.) tussock grasslands on rolling plains with some low tree overstorey of gidgee and other species although the area is generally characterised by a lack of tree and shrub cover.

The Mitchell grass grassland occurs on the deep cracking clays over tertiary alluvium. Grasses are dominated by curley Mitchell (Astrebla lappacea) and barley Mitchell (Astrebla pectinata) with other Mitchell grasses and Flinders grasses (Iseilema spp.) occurring also. Scattered shrubs on the generally treeless areas include gundabluei (Acacia victoriae), mimosa (A. farnesiana), Georgina gidee (A. georginae) — west of Georgina River, whitewood (Atalaya hemiglauca)andcassias (Senna spp.). A large variety of forbs grow on the bare soil between grass tussocks after rain (Kerle, 1996, Mills 1980, Mills & Lee 1990, Nelder 1984 & 1991, Sattler & Williams 1999 and Turner et. al. 1978 & 1993).

Coolibah (Eucalyptus coolabah/microtheca) low open woodland over open grassland occurs in patches across the region in association with low-lying plains and periodically flooded drainage lines are. Supplejack (Ventilago viminalis), whitewood, swamp boxes (Lophostemon spp.) and gutta-percha (Excoecaria parvifolia) grow in association with the coolibah. Other common grass species include, silky browntop (Eulalia aurea) and golden beard grass (Chrysopogon fallax), blue grasses (Dichanthium spp.), Panicum spp. and Eriochloa spp. River red gum (Eucalyptus camaldulensis) open woodland can be found instead of coolibah along some watercourses (Kerle, 1996).

Many of the seasonal shallow lakes or swamps are covered by bluebush (Chenopodium auricomum) low open shrubland with an understorey of ephemeral grassland, which grows after rain. The grasses include pepper grass (Panicum aevinodei), beetle grass (Diplachne spp.)and a range of forbs. In Lake Woods, near Elliott in the Northern Territory, lignum (Muehlenbeckia florulenta) occurs as a low shrubland over pepper grass (Kerle, 1996).

For a list of rare and threatened flora and vegetation descriptions of the bioregion in Queensland refer to Sattler & Williams (1999).

Fauna

The tussock grasslands typical across this bioregion determine many of the characteristics of the fauna. Vertebrate species diversity is generally low and there is an absence of most arboreal birds. Several species found within the region experience a ‘boom-bust’ population cycle as their population density peaks and declines dramatically in response to rainfall patterns. Examples of species found with the Mitchell Grass Downs that experience dramatic population fluctuations include the long-haired rat (Rattus villosissimus), flock bronzewing (Phaps histrionica) and letter-winged kite (Elanus scriptus).

The cracking clay soils support a very high diversity of large elapid snakes, several endemic reptile species, and very high densities of several grassland birds and small marsupials. Species include the Spencer’s monitor (Varanus spenceri), the speckled brown snake (Psendonaja guttata), the singing bushlark (Mirafra javanica) and the long-tailed planigale (Planigale ingrami). The endangered dasyurid mammal, the Julia Creek dunnart (Smithopsis douglasi) is largely restricted to this bioregion.

The seasonally flooded shallow lake systems provide rich habitat for waterfowl and migratory waders. The wet season brings high densities of burrowing frogs, and the formation of swamps, typically surrounded by bluebush. These are nationally and internationally significant for breeding waterbirds including pelicans, ibis, herons, terns and ducks. The grasslands also form a major summering ground for some migratory birds, such as the little curlew (Numenius minutus) and oriental pratincole (Glareola maldivarum). For more details see: www.savanna.ntu.edu.au/information/savannaexplorer.html.

For a list of the fauna surveys and rare and threatened fauna in Queensland refer to Sattler & Williams (1999).

Land Tenure & Use

Land tenure

Land tenure is mainly leasehold with some freehold occurring in the south-east of the region within Queensland. Significant conservation areas in Queensland include, Astrebla Downs National Park, a large part of Diamantina National Park, Camooweal Caves National Park and parts of Bladensburg and Lochern National Parks. In the Northern Territory’s 83,144 sq. kms portion of the bioregion, of land is set aside for conservation purposes, less than 1% is Aboriginal freehold land and 91% is dedicated to pastoral leases and freehold land (Connors, et. al., 1996).

Land use

Much of the region is dependent on the underlying Great Artesian Basin for water. Land within the bioregion is almost entirely dedicated to pastoralism, due to the extensive occurrence of palatable grasses, with cattle grazing dominating in the Northern Territory, with cattle and sheep grazing occurring in Queensland (Woinarski, et. al., in prep.). Reserved areas within the bioregion are Connell’s Lagoon Conservation Reserve and Junction Waterhole Stock Reserve in the Northern Territory and Astrebla Downs National Park, parts of Bladensburg N.P., Camooweal Caves N.P., Diamantina N.P., Idalia N.P. and Mariala N.P. in Queensland.

Condition Of The Landscape

Land degradation

Mitchell grass pastures are generally considered relatively resilient to grazing (Tothill and Gillies 1992). However the widspread occurrence of artificial waters means that most areas are accessible to grazing by domestic, native and feral animals increasing the chances of overgrazing , especially closer to the waters.

Land degradation in the Northern Territory, due to over-grazing, has been recorded, affecting some of the less extensive habitats such as bluebush (Chenopodium auricomum) swamps. Bluebush is highly palatable and is selectively grazed in preference to other pasture types (Connors, et. al., 1996). Invasive species such as the prickly acacia (Acacia nilotica) mesquite (Prosopis spp.)and parkinsonia (Parkinsonia aculeata) are also a problem in the region. Clearing of vegetation on the slopes of north-east corner of this bioregion, within Queensland, occurred in the 1980s and 1990s. This clearing has been mainly of gidgee (Acacia cambagei)

The State-wide Landcover And Tree Study (SLATS) undertaken by the Queensland Department of Natural Resources, provides vegetation cover and cover change information using Landsat Thematic Mapper ™ satellite imagery. SLATS provides baseline land cover mapping over the entire State of Queensland (www.dnr.qld.gov.au/resourcenet/veg/slats/index.html).

Pest species

Feral animals occurring across large areas of the bioregion are pigs and feral horses. Feral cats also impact on native marsupials and birds. Rabbits also have an impact on natural systems, where lighter soils abound, and pastoral operations and foxes can also exist in high numbers, relative to the population of rabbits, and they too can impact on natural ecosystems.

Donkeys, cane toads and goats all exist within the bioregion. Connors, et. al., (1996) also lists the house sparrows, black rats and the house mice as occurring within the region.

Connors, et. al., (1996) lists sixteen weed species and twenty-three introduced plant species recorded in the Northern Territory portion of the Mitchell Grass Downs bioregion. Invading shrubs such as prickly acacia (Acacia nilotica), parkinsonia (Parkinsonia aculeata) and mesquite (Prosopis limensis) tolerate the harsh conditions and have invaded large areas of land in an aggressive manner. Annual weed species such as parthenium weed (Parthenium hysterophorus) are invading the eastern parts of the bioregion and represent a significant threat, establishing readily in areas where pasture cover has been degraded.

With a general lack of tree cover throughout the region, the introduction of woody weeds has the potential to considerably change the vegetation structure and the spread of prickly bushes along waterways could also impact on waterbird nesting sites (www.savanna.ntu.edu.au/information/savannaexplorer.html).

Social & Economic Aspects

People

The Mitchell Grass Downs bioregion includes the towns of Tambo at the eastern end of the region in Queensland, and Elliott in the western extreme of the region in the Northern Territory.

The population for the area according to the 1996 Census is 16,500 with Longreach’s population of 3,766 being the largest in the region. Longreach serves as a major regional administration centre and the Hall of Fame is a tourist attraction for the area. Other towns in the region include Tambo (population: 378), at the eastern end of the region, Hughenden (population: 1,444), Blackall (1,433) and Winton (1,142). Smaller centres with populations under one thousand include Richmond (733), Julia Creek (519), Elliott (432), Tambo (378), Camooweal (258), Boulia (243) and Dajarra (203). These towns primarily serve the pastoral industry.

The bioregions is within the ATSIC regions of Tennant Creek, Rockhampton and Mount Isa and are managed by their respective regional councils, Yapakurlangu, Central Queensland and Mount Isa and Gulf (McLennan, 1997). For more information on the Aboriginal people of this region refer to Horton, (1994) and the relevant websites in the reference list.

Resources, References & Contacts

Publications

Connors G., Oliver B., & Woinarski, J. 1996, Bioregions in the Northern Territory: Conservation Values, Reservations Status and Information Gaps. Final report to ANCA National Reserves System Cooperative Program (Project N607), Parks and Wildlife Commission of the Northern Territory, Palmerston, Northern Territory. (www.nt.gov.au/paw/fauna/bau/intro.htm).

Horton, D. R. 1994, The Encyclopaedia of Aboriginal Australia, Aboriginal Studies Press for the Australian Institute of Aboriginal and Torres Strait Islander Studies, Canberra, ACT.

Kerle, J.A. 1996, Bioregions of the Northern Territory. Draft report Conservation Commission of Northern Territory, Palmerston, Northern Territory.

McLennan. W. 1997, 1994 National Aboriginal and Torres Strait Islander Survey: Social Atlas, Australian Bureau of Statistics, Canberra, ACT.

Mills, J.R. 1980 ‘Land Systems. In Western Arid Region Land Use Study — Part2. Technical Bulletin No. 22, Division of Land Utilisation, Queensland Department of Primary Industries, Brisbane.

Mills, J.R. and Lee, A.N. 1990 ‘Land Systems. In Western Arid Region Land Use Study — Part 3. Technical Bulletin No. 29, Division of Land Utilisation, Queensland Department of Primary Industries, Brisbane.

Morton, S.R., Short, J., & Barker, R.D. with an Appendix by Griffin, G.F., & Pearce, G. 1995, Refugia for Biological Diversity in Arid and Semi-arid Australia, Department of the Environment, Sport and Territories, Canberra, ACT.

Nelder, V.J. 1984 Vegetation Survey of Queensland- South Central Queensland. Queensland Botany Bulletin No.3. Department of Primary Industries, Brisbane.

Nelder, V.J. 1991 Vegetation Survey of Queensland- Central Western Queensland. Queensland Botany Bulletin No.9. Department of Primary Industries, Brisbane.

Sattler, P. & Williams, R. (eds.) 1999, The Conservation Status of Queensland’s Bioregional Ecosystems, Environmental Protection Agency, Brisbane, Queensland.

Thackway, R. & Cresswell I.D. 1995, An Interim Biogeographical Regionalisation for Australia: a Framework for Setting Priorities in the National Reserves System Cooperative Program, Australian Nature Conservation Agency, Canberra, ACT.

Tothill, J.C. and Gillies, C. 1992 The Pasture Lands of Northern Australia. Their Condition, Productivity and Sustainability. Tropical Grassland Society of Australia. Occasional Publications 5.

Turner, E.J. 1978. ‘Land Systems. In Western Arid Region Land Use Study — Part 4. Technical Bulletin No. 23, Division of Land Utilisation, Queensland Department of Primary Industries, Brisbane.

Turner, E.J., McDonald, W.J.F., Ahern, C.R. and Thomas, M.B. 1993. Western Arid Region Land Use Study — Part 5. Technical Bulletin No. 30, Division of Land Utilisation, Queensland Department of Primary Industries, Brisbane.

Woinarski J., Fensham, R., Whitehead, P. & Fisher, A., with map production by Verhagen, C. in preparation, Biodiversity in the Australian Rangelands: a Review of Changes in Status and Threatening Processes. Draft report prepared as a resource document for Project 3: Developing an Adaptive Framework for Monitoring Biodiversity in Australia’s Rangelands, of the National Land and Water Resources Audit, Theme 4 (Rangelands monitoring) by the Tropical Savannas Cooperative Research Centre, Darwin, Northern Territory.

Websites and contacts

Aboriginal languages of Australia:

http://www.dnathan.com/VL/

Aboriginal Studies WWW Virtual Library:

http://www.ciolek.com/WWWVL-Aboriginal.html

Australian Landcare Council:

www.dpie.gov.au/agfor/landcare/org/alc.html.au

Aboriginal Torres Strait Islanders Commission (ATSIC):

www.atsic.org.au/about_atsic/board_regional_councillors/regional_information.htm

Australian Geological Survey Organisation, Geology of Australia:

www.agso.gov.au/map/

Bureau of Meteorology, Climate averages:

www.bom.gov.au/climate/map/climate_avgs/a17.shtml

http://www.bom.gov.au/climate/map/climate_avgs/a37.shtml

Bureau of Meteorology, Temperature and rainfall graphs: www.bom.gov.au/climate/forms/map_forms/new_imagemaps/qld_name.html

Bureau of Rural Sciences, Digital Atlas of Australian Soils:

www.affa.gov.au/content/output.cfm?ObjectID=D2C48F86-BA1A-11A1-A2200060B0A05758

Department of Mines and Energy, Queensland:

www.dme.qld.gov.au/gsd/index.htm

Department of the Environment and Heritage, Normalized Difference Vegetation Index (NDVI) information including bioregional information:

www.environment.gov.au/erin/ndvi/index.html

National Property Management Planning Campaign, The Future profit program:

www.dpi.qld.gov.au/ruraldev/futureprofit/Welcome.html

Queensland Department of Natural Resources. ‘Long Paddock’:

www.dnr.qld.gov.au/longpdk

Queensland Department of Natural Resources. ‘Silo’:

www.dnr.qld.gov.au/resourcenet/climate/#silo

Queensland Department of Natural Resources. Patched Point Dataset and Data drill:

www.dnr.qld.gov.au/resourcenet/silo/index.html,

Queensland’s Environmental Protection Agency. National Park information, animal and plant species information including rare and threatened species:

www.env.qld.gov.au

Queenslands Parks and Wildlife Service:

www.env.qld.gov.au/environment/park/discover/

Rural Lifestyles Queensland:

www.rlq.dcilgp.qld.gov.au

State-wide Land cover and Tree Study (SLATS) Vegetation cover and cover change information using Landsat Thematic Mapper ™ satellite imagery:

www.dnr.qld.gov.au/resourcenet/veg/slats/index.html

Tropical Savanna Co-operative Research Centre:

www.savanna.ntu.edu.au/information/savannaexplorer.html

Link to the Map Maker to make a map using this information.

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