Brigalow Tropical Savanna
The Brigalow Tropical Savanna is a biodiverse biome located in Australia, covering approximately 132,000 square miles (343,000 square kilometers). This region features unique acacia-wooded grasslands that act as a transitional zone between the tropical rainforests of northeastern Australia and the semi-arid areas of Queensland. Notably, the savanna includes the Northern and Southern Brigalow Belts, with the Southern Belt extending into New South Wales. The vegetation primarily consists of the endemic Brigalow tree (Acacia harpophylla), alongside other eucalyptus species, which contribute to the region's distinctive open-forest communities.
The savanna is home to an impressive variety of wildlife, with over 400 bird species recorded, as well as endangered mammals like the northern hairy-nosed wombat and the bridled nail-tail wallaby. However, human activities such as agriculture and mining have significantly impacted the ecosystem, leading to habitat destruction and the introduction of invasive species, which threaten native flora and fauna. Conservation efforts face challenges from land clearing, monoculture farming practices, and climate change, although the region's geographical features may help mitigate some climatic impacts. Understanding the complexities of this ecosystem highlights the importance of preserving its unique biodiversity and addressing the ongoing threats it faces.
On this Page
Subject Terms
Brigalow Tropical Savanna
- Category: Grassland, Tundra, and Human Biomes.
- Geographic Location: Australia.
- Summary: This biodiverse woodland region, running through a long stretch of Australia, is home to several endangered species that face further dangers in the future.
The Brigalow Tropical Savanna biome consists of the Northern and Southern Brigalow Belts, expanses of acacia-wooded grassland separating the tropical rainforest of the northeastern Australian coast from the semi-desert region of Queensland. The Southern Belt extends just past the Queensland/New South Wales border, where the eastern Australian temperate forests begin.
At 132,000 square miles (343,000 square kilometers), the Brigalow tropical savanna covers a wide area that includes sand and clay deposits, basalt and alluvium, the coal-producing Bowen Basin, the Great Artesian Basin, the sandstone gorges of the Carnarvon Range (part of the Great Dividing Range); and the agriculturally rich Darling Downs. The biome is drained by the Fitzroy River system, running eastward toward the coast; the Belyando and Burdekin Rivers, near the tropic; and the Maranoa, Warrego, and Condamine rivers, draining into the Murray-Darling basin in the southwest.
Vegetation
Brigalow (Acacia harpophylla) is an endemic (unique to this biome) tree here, growing up to 82 feet (25 meters) tall in clay soils. It forms extensive open-forest communities with gidgee (Acacia cambagei); these forests are also home to smaller populations of A. tephrina, A. georginae, and A. argyrodendron. Overstory species in the forests include eucalyptus such as the coolabah (Eucalyptus microtheca) and Dawson River blackbutt (Eucalyptus cambageana), as well as the belah (Casuarina cristata). In the western regions, where rainfall is heavier, gidgee outnumbers brigalow. In the more humid valleys, brigalow mixes with C. cristata. Though gidgee has a limited capacity to resprout after fire damage, brigalow resprouts freely from the butt, roots, and living stems if necessary.
The brigalow once covered most of this area, but has typically been cleared by European settlers to make way for agricultural land and a more diverse woodland landscape. Much of the once-extant wildlife has become extinct, endangered, or threatened as a result of the destruction of habitat. The grasslands continue to be threatened today by introduced pasture grasses like buffelgrass (Pennisetum ciliare) and other invasive weeds. The clearing of brigalow and poplar box (Eucalyptus populnea) is a current threat, while protected areas are often limited to small park areas.
Fauna
The savanna boasts over 400 bird species being recorded in the area. Other animals in the area include the wingless dung beetle (Onthophagus apterus) and numerous wallabies. The bridled nail-tail wallaby (Onychogalea fraenata), an endangered species, lives in the Taunton and Idalia National Parks, and is of scientific interest because of its unusually hardy immune system, which is better able to fight parasites and viruses than that of other marsupials. A critically endangered mammal, the burrowing northern hairy-nosed wombat (Lasiorhinus krefftii) lives in Epping Forest National Park. Although its range at the start of the twentieth century comprised most of New South Wales, Victoria, and Queensland, the population was thought to be less than two hundred. However, by 2021, its population had risen to more than three hundred, causing conservationists to be cautiously optimistic about its future. One of the threats to the wombat, apart from human encroachment, has been the introduction to its habitat of African buffelgrass, which outcompeted the grasses on which the wombat feeds.
The Fitzroy River turtle (Rheodytes leukops) is an endemic reptile, found only in the Fitzroy River watershed, and the sole survivor of the Rheodytes genus. Able to absorb oxygen from the water while submerged, through special subcutaneous sacs, it is an omnivore with a taste for everything from freshwater sponges to crustaceans. The turtle is also known for its acute sense of smell. Human activity, mainly agriculture and mining, has had a major effect on the turtle. The clear, clean water it was used to has become turbid and polluted; portions of the Dawson River that form part of its habitat have registered a water alkalinity range deleterious to the turtle's skin; and high levels of salinity, which are frequent by-products of forest clearing, have also impacted the species. It is currently unclear whether the species is able to propagate successfully in the wild.
A serious threat to the Fitzroy River turtle is the proposed Nathan Dam, which will be Queensland's fourth-largest dam. It will dam the Dawson River to irrigate 74,130 acres (30,000 hectares) of agricultural crops, primarily cotton. Pesticide and fertilizer in the runoff, joined by high levels of sediment, will jeopardize not only the turtles, but migratory birds and many species of fish, some of them endemic.
Global warming and climate change do not seem to have markedly altered the Brigalow tropical savanna due in part to its protected position between the rainforest-bordered ocean and the arid lands at its opposite extent. Endemic species here are not likely to be unduly stressed by future climate change. More dramatic threats are seen, however, as coming from land clearing, agricultural practices that favor monoculture and invasive species, displacement of native species as a secondary effect of grazing, flooding from dam construction, and habitat fragmentation.
Bibliography
"About Northern Hairy-Nosed Wombats." Queensland Government, 7 Oct. 2021, www.qld.gov.au/environment/plants-animals/conservation/threatened-wildlife/threatened-species/featured-projects/northern-hairy-nosed-wombat/about-northern-hairy-nosed-wombats. Accessed 29 Oct. 2024.
Burrows, W. H., et al. Native Pastures in Queensland: Their Resources and Management. Queensland Government Press, 1988.
Grice, T. C., and S. M. Slatter, editors. Fire in the Management of Northern Australian Pastoral Lands. Tropical Grassland Society of Australia, 1990.
Huntley, Brian J., and Brian Harrison Walker, editors. Ecology of Tropical Savannas. Springer-Verlag, 1982.
Moll, Don, and Edward O. Moll. The Ecology, Exploitation, and Conservation of River Turtles. Oxford University Press, 2004.