Brigalow tropical savanna

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Townsville, Australia Photograph by John Morrison

The bulk of the Brigalow Belt forms a wide band of inland habitats wedged between wetter coastal habitat and the drier semi-arid zone to the west. The region is characterized by the natural overstory dominance of brigalow (Acacia harpophylla) in many lowland woodlands of the region, although other eucalypt woodlands are also present. The majority of the brigalow communities in the ecoregion have been cleared for cropping and pasture improvement. Several previously widespread communities are regarded as endangered, and a number of animals are threatened as well.

Location and General Description



 

The Brigalow Belt covers a wide latitudinal range, stretching from Townsville (19°15’S) to the New South Wales/Queensland Border (28°35’S). At a local bioregional level the Brigalow Belt is often separated into two regions to differentiate between areas of tropical summer rains and warm year round temperatures in the north, and areas subject to cooler winter temperatures and less extreme summer rainfall dominance in the south. There is a general reduction in rainfall from coastal areas in the east to semi-arid areas in the west. In the east, near coastal areas, rainfall is above 750 millimeters (mm), and decreases to below 500 millimeters in the west. Despite these climatic gradients, the ecoregion comprises a readily identifiable system of habitats formed on ranges and associated drainage areas. They tend to run north to south, in accordance with underlying faulting patterns. The majority of the Brigalow Belt drains eastwards to the Coral Sea through the Belyando-Burdekin system and the Fitzroy catchment, which constitutes much of the central portion of the Brigalow Belt. Waters from the southwest of the Brigalow Belt enter the Murray-Darling system, via the Maranoa, Warrego, and Condamine Rivers.

The Brigalow Belt has a diversity of underlying geologies. The major sedimentary basins in the north are the coal bearing Permian-Triassic Bowen Basin, and the Carboniferous-Devonian Drummond Basin. The south mainly overlies sediments of the Great Artesian Basin, with Cretaceous, Jurassic, and deeply weathered sediments that are overlain in some areas with Cretaceous deposits forming clay or sandsheets. Sediments near the junction of the Bowen Basin and Great Artesian Basin in Queensland’s Central Highlands have become dissected to form gorges, scarps, and plateaus of the Sandstone Belt. Recent deposits are found in the west and southwest of the region in the Belyando and Darling drainages. A band of volcanics runs through the mid-west of the Brigalow Belt. Carboniferous basalts in the north are replaced by Tertiary basalts that provide fertile areas further south in the Peak and Darling Downs and overlay sediments of the Sandstone Belt in the Carnarvon range. A smaller band of parallel volcanics is found further east, and is broken by the outlet of the Fitzroy River to the coast from its largely inland basin, which also contains some Tertiary deposits. Palaeozoic plutonics outcrop in the north of the region and in the Anakie Inlier. They are principally Carboniferous and Devonian granites and granitoids. The diversity of landforms and geologies create a diversity of soil types; there are generally hard alkaline duplexes and stony lithosols on the ranges interspersed with cracking clays and alluvium on areas of shallow relief.

Clay soils of the ecoregion support the brigalow (Acacia harpophylla) woodlands, after which the region is named. Brigalow naturally covered around 40 percent of the region. Much of the remainder of the region is eucalypt woodlands and forests, particularly ironbarks (Eucalyptus crebra and E. melanophloia) on ridges, and E. melanophloia on lower elevations, ranges, and plains. Poplar box (E. populnea) woodlands occur on lowlands. Ranges and hills of the region host Eucalyptus crebra and other ironbarks, E. decorticans, Corymbia citriodora, and Acacia catenulata or A. shirleyi. Adjacent sand plains are dominated by Eucalyptus spp. and Callitris spp. Common species on plains and undulating rises include Eucalyptus populnea, E. melanophloia, E. mollucana, and C. tesselaris. Common species on alluvium include Eucalyptus camaldulensis, E. tereticornis, E. coolibah, and E. largiflorens.

Pockets of dry rainforest occur in gullies and wetter microclimates throughout the Brigalow Belt, and sometimes form associations with Casuarina cristata and brigalow. Brigalow is replaced by gidgee (Acacia cambadgei) in drier areas, generally becoming dominant in the west of the region. Bluegrasses (Dichanthium spp.) form grasslands in some areas, particularly on clays in the Peak Downs area. The Sandstone Belt forms a distinct floristic region within the Brigalow Tropical Savannas, and possesses varied communities dominated by eucalypt woodlands and forest, but also contains restricted communities such as vine thickets within moist gorges of the belt. Cypress Pine (Callitris glaucophylla) woodlands are common on sandy soils in the west of the Sandstone Belt. This ecoregion does touch the coastline, with mangroves and other coastal communities such as salt flats and strand vegetation.

Biodiversity Features

The Brigalow Belt’s most distinctive feature was the large tracts of brigalow scrub found throughout the region. Although found in adjacent ecoregions, the size and diversity of brigalow communities was unique. Dichanthium dominated grasslands within the Brigalow Belt also represent communities distinct from those found in much more extensive grasslands further west. The relatively dry Brigalow Belt isolates wetter Queensland Tropical Rainforests from the temperate forests of southeastern Queensland and New South Wales (Eastern Australian temperate forests ecoregion). Dry rainforest vegetation in the region includes some endemic species such as Cadellia pentastylis and Macropteranthes leichhartii.

Ironbark and eucalypt communities of these ranges are largely typical of communities in other eastern Queensland ecoregions, however, the Sandstone Belt and associated basaltic plateaus represent an area of remarkable diversity and endemism across taxonomic groups. Endemic eucalypts include E. rubiginosa, Corymbia bunites, and the inland white mahogony (Eucalyptus sp.) A number of other endemics occur on Isla Gorge and Blackdown Tableland. Many species with dry country affinities are restricted to the flat plateau tops, while the gorges preserve floras with affinities to the moister east coast. Two endangered mammals, the northern hairy-nosed wombat (Lasiorhinus kreftii CR) and the bridled nailtail wallaby (Onychogalea fraenata EN) were once widespread in eastern Australia but are now endemic to single locations within the Brigalow Belt.

Other animals endemic to this ecoregion include the Fitzroy River turtle (Rheodytes leukops VU), flecked fossorial lizard (Calyptotis temporalis), yellow-lipped scalyfoot (Delma labialis), unadorned rock-wallaby (Petrogale inornata), and the russet-tailed thrush (Zoothera heinei). A number of species once found in this ecoregion are now extinct, including the paradise parrot (Psephotus pulcherrimus EX). The dusky flying-fox (Pteropus brunneus EX) was restricted to the Percy Islands offshore, but is also now presumed extinct.

Current Status

Eucalypt woodlands and forests of the regions upland’s are largely structurally intact. Fertile lowlands however, have been extensively cleared. Of 27 regional ecosystems listed as endangered by Young et al, 18 are found on alluvial or clay plains, and 7 are associated with lowlands or undulating country. Most endangered regional ecosystems are restricted in their natural distribution due to geological or ecological specialization (e.g. mound spring communities). The exceptions are brigalow and poplar box communities. Once widespread across the region, brigalow communities have been cleared by as much as 87 percent in the last 70 years. Their affinity for fertile clay soils places them at odds with the interests of cropping and pastureland improvements and development. As a result 12 brigalow associations are considered endangered, eight of which are dominated by A. harpophylla. The dominance of altered landscapes in the Brigalow Belt is regarded by Thackway and Cresswell to be the most significant obstacle to successful conservation planning within the region.

There are ten notable major conservation reserves of the Brigalow Belt. They range in size from the Taunton NP, at 115 kilometers2, to the Carnarvon NP at 2980 kilometers2. The habitat types protected within these reserves range from woodlands, savanna, eucalypt forests, vine thicket and montane forests to moist gorge communities and coastal wetlands. The reserves, from smallest to largest, are: the Taunton, Epping Forest, Dipperu, Bowling Green Bay, Goodedulla, Chesterton Range, Homevale, Blackdown Tableland, Expedition, and Carnarvon.

Patterns of reservation in the Brigalow Belt are highly biased towards relatively undisturbed and widespread rugged upland habitats. Lowland regions with fertile soils and high economic potential are poorly reserved, and continue to be cleared. The extent of land clearing is roughly correlated with the proportion of freehold tenure (which is in turn related to productivity). Freehold tenure is markedly more prevalent in the southern Brigalow Belt, while control of tree clearing was introduced in September of 2000, some ecoystems are still not well protected.

Remaining brigalow communities are still underrepresented in reserve systems, with many small parks (not listed above) reflecting the fragmented nature of the remnant vegetation. Five grassland communities of the region are considered endangered; four of them dominated by bluegrass (Dichanthium spp.). Dichanthium grasslands are not adequately protected by the current reserve system. Only three of 13 endangered plant species are represented in conservation reserves. The Sandstone Belt represents the most significant area of relatively undisturbed habitats in the ecoregion. Its disproportionately well protected habitats are of great conservation value, however, they are also scenic and of low value for agriculture and grazing, and are therefore politically relatively easy to preserve. Future reserves must target uncleared lowland habitats to preserve the unique brigalow and Bluegrass communities of the region.

Two small parks, Taunton and Epping Forest, are particularly significant for endangered fauna. Brigalow scrubs and eucalypt woodlands in Taunton National Park housed the only wild population of bridled nailtail wallabies until recent reintroductions into Idalia National Park, and Epping Forest National Park harbors the only free-living colony of northern hairy-nosed wombats. Sandstone parks such as Isla Gorge, Blackdown Tableland, and to a lesser extent Carnarvon National Park are much more significant for centers of endemism and for plant species.

Types and Severity of Threats

Continued clearing of lowland brigalow and poplar box communities and the conversion of native grassland to cultivation represent the major threats to the remaining lowland ecosystems of the region. The effects of land clearance are significantly increased by pasture "improvement" practices advocated by some government bodies. The combination of bulldozing and introduction of exotic pasture, particularly buffelgrass (Cenchrus ciliaris), has been shown to significantly reduce floristic diversity of Brigalow Belt Communities. The communities subject to these practices are those poorly represented in conservation reserves.

The invasive weed Parthenium hysterophorus constitutes a significant threat to many areas of the central Brigalow Belt. This is particularly true in Dichanthium grasslands where once Parthenium hysterophorus has attained local dominance, pastures are rendered unproductive and may be converted to cropping to avoid loss of income. A proposed dam and irrigation scheme on the Dawson River will encourage clearing of the small remnants of native vegetation that remain in the area, and will inundate endangered mound spring habitats of the region. The effects of grazing on natural systems are relatively benign in comparison to land clearing, however, cattle have been directly implicated in the decline of the northern hairy-nosed wombat and the introduction of exotic fodder species threatens the natural diversity and composition of uncleared native woodlands.

Justification of Ecoregion Delineation

The Brigalow Tropical Savannas comprise the ‘Brigalow Belt North’ Interim Biogeographic Region of Australia (IBRA) and the Queensland portion of the ‘Brigalow Belt South’ IBRA. The ecoregion is largely defined by the presence of brigalow (Acacia harpophylla) vegetation.

Additional Information on this Ecoregion

Further Reading

  • Anonymous. 1999. Parks and Wildlife Management Services (Central Region). Environmental Protection Agency, Brisbane, Australia.
  • Crossman, D.G., C.N. Johnson, and A.B. Horsup. 1994. Trends in the population of the northern hairy-nosed wombat, Lasiorhinus kreftii, in Epping Forest National park, central Queensland. Pacific Conservation Biology 1: 141-149.
  • Fairfax, R.J., and R.J. Fensham. 2000. The effect of exotic pasture development on floristic diversity in central Queensland, Australia. Biological Conservation 94: 11-21.
  • Fensham, R.J. 1998. Mound springs in the Dawson River Valley, Queensland. Vegetation-environment relations and consequeces of a proposed impoundment on botanical values. Pacific Conservation Biology 4: 42-54.
  • Fensham, R.J. 1999. Native grasslands of the central highlands, Queensland, Australia. Floristics, regional context and conservation. Rangelands Journal 21: 82-103.
  • Fensham, R.J., J.C. McCosker, and M.J. Cox. 1998. Estimating clearance of Acacia-dominated ecosystems in central Queensland using land-system mapping data. Australian Journal of Botany 46: 305-319.
  • Graetz, R.D., M.A. Wilson, and S.K. Campbell. 1995. Landcover Disturbance over the Australian Continent. Biodiversity Unit, Department of the Environement Sport and Territories, Canberra, Australia. ISBN: 0642229058
  • Hilton-Taylor, C. 2000. The IUCN 2000 Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom. ISBN: 2831705657
  • Johnson, R.W. 1984. Flora and vegetation of the Brigalow Belt. Pages 41-59 in A. Bailey, editor. The Brigalow Belt of Australia. The Royal Society of Queensland, Brisbane, Australia. ISBN: 0724222723
  • McCarroll, S.M., and B.A. Forster. 1999. Agricultural Land Evaluation along the lower Dawson River. Central West Region, Department of Natural Resources, Brisbane. ISBN: 0734516126
  • Neldner, V.J. 1984. Vegetation Survey of Queensland (South Central Queensland). Department of Primary Industries, Brisbane, Australia. ISBN: 0724223525
  • Strahan, R. editor. 1998. The mammals of Australia. Australian Museum/Reed New Holland. Syndey, Australia. ISBN: 1876334886
  • Thackway, R., and I.D. Creswell. 1995. An Interim Biogeographic Regionalisation for Australia: A framework for establishing a national system of reserves, Version 4. Australian Nature Conservation Agency, Canberra, Australia.
  • Young, P.A.R., B.A. Wilson, J.C. McCosker, R.J. Fensham, G. Morgan, and P. M. Taylor. 1999. Brigalow Belt. Pages 11/1-11/81 in P. Sattler and R. Williams, editors. The Conservation Status of Queensland's Bioregional Ecosystems. Environmental Protection Agency, Brisbane, Australia.

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

 

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Citation

Fund, W. (2014). Brigalow tropical savanna. Retrieved from http://www.eoearth.org/view/article/150781

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