Simpson Desert Ecosystem

Category: Desert Biomes.

Geographic Location: Australia.

Summary: This desert has the world’s largest parallel sand dune structure. Despite harsh conditions, it is home to diverse fauna and flora.

More than two-thirds of the Australian landmass is classified as arid or semiarid, and the Simpson Desert is one of the most arid parts of the continent. Areas of the Simpson have long-term annual average rainfall of 6 inches (140 millimeters), but the rainfall is far from consistent; it occurs in random bursts of thunderstorms every few years, with exceedingly dry periods in between. This limited rainfall and a temperature range of 32–122 degrees F (0–50 degrees C) mean that evaporation rates far exceed rainfall rates.

The Simpson covers 67,568 square miles (175,000 square kilometers) in the corners of the states of Queensland, South Australia, and the Northern Territory. It is bordered on the south by Warburton Creek and the Tarari Desert, on the west by the Finke and Todd rivers, and on the east by the Diamantina and Georgina rivers.

The Simpson Desert is characterized by vast dune fields. The red sand dunes run 99 miles (160 kilometers) in a north-south direction and can reach 131 feet (40 meters) in height. Linear sand dunes are created when bimodal winds (in this case, southeasterlies and southwesterlies) blow the sand particles. The sand dunes are of Pleistocene origin and have a thin, 7-foot (2-meter) layer of sand atop consolidated clays.

The watercourses of the region rarely flow, but when they do, the flows are slow-moving but large. Although Warburton Creek has water in it every few years, Kati Thanda- Lake Eyre, into which the Warburton flows, fills completely only two to three times a century on average and takes about two years to dry up. The water takes a long time to reach the lake bed; for example, abundant rain that arrived in late 2019 did not begin filling the lake until the following March. In July 2022, Kati Thanda-Lake Eyre stretched 105 miles (170 km) north to south. While arid above the ground, the Simpson Desert sits atop the Great Artesian Basin, a vast underground aquifer that receives water falling on the west of the Great Dividing Range thousands of miles (kilometers) away.

Flora

During wet years, the tops of the sand dunes are held together by vegetation, but more typically, huge sandstorms are whipped up by winds that are unchecked by topography. During decades of drought, the parallel red sand dunes are vegetated with isolated hummocks of sandhill canegrass and nitre bush. Both of these plants provide support and structure in the shifting sands of the dune tops, and within this structural support, small native mammals and reptiles make burrows for homes.

The swales are vegetated by acacia and hakea shrubs, with coolabah eucalypts lining the edges of the watercourses and lignum swamps filling the floodouts, areas flooded when the watercourses flow. Other hallmark plants of the biome include canegrass (Zygochloa paradoxa and Triodia basedowii), a hardy grass that grows on the tips of sand dunes; parrot bush (Crotalaria cunninghamii), with narrow, yellow-green flowers; and spinifex grass, which also grows on sand dunes.

Fauna

Despite being a highly inhospitable environment, the Simpson Desert originally supported diverse fauna, a recorded 34 mammal, 231 bird, and 125 reptile species. While arid Australia is an epicenter of mammalian extinctions worldwide, several unique species have persisted—possibly because introduced predators are less able to attain the densities needed to drive these small extant species extinct. Crest-tailed mulgara, for example, are carnivorous marsupial predators with a sandy-colored coat and a black crestlike tail; they inhabit burrows within the dune fields.

On the edge of the Simpson lives the kowari, another carnivorous marsupial, with a black, bushy tail. The kultarr is a smaller marsupial carnivore that stands upright like a tiny kangaroo and appears to hop when fleeing. The dusky and fawn-hopping mice are Australian native rodents that are endemic (found nowhere else) to this region; they hop along like tiny kangaroos as they search for seeds and insects.

Perhaps the most iconic species is the Eyrean grasswren, which is endemic to the Lake Eyre basin. It was recorded in the 19th century and then not observed again until 1976. The Eyrean grasswren feeds on seeds and small invertebrates that it collects while hopping around on the ground with its tail cocked.

Other birds of the dunes and swales are the whitefaces, zebra finches, emus, Australian bustards, and raptors such as whistling kites, brown falcons, and wedge-tailed eagles. When rainfall fills the watercourses and lakes of the region, birdlife erupts, and mass breeding events occur. Species of avocet, ibis, stilt, pelican, cormorant, and duck migrate in from thousands of miles (kilometers) away to use the short increase in resources for breeding.

Human Settlement

Aboriginal people have been living alongside water in and around the Simpson Desert for thousands of years. They were present when giant rhinoceros-size marsupials, Komodo-dragon-sized goanna, and 33-foot (10-meter) snakes and crocodiles roamed the region, tens of thousands of years ago. The tracks of Euwinia grata, a gigantic wombat, can be seen in the rocks along Warburton Creek.

Explorer Charles Sturt was the first European to see the Simpson, during 1844–46, but it was not until 1936 that Ted Colson became the first European to cross it entirely. Captain James Lewis’s report of his expedition along Warburton Creek in 1874–75 described a large population of Aboriginal people sustaining themselves around isolated water holes on bountiful fish from the creek, supplemented with smaller marsupials like boodies and possums, and herbage like nardoo. These water holes persisted despite a lack of rain for several years previous. Lewis reported on groups of Aboriginal people who had moved deep into the desert during rainy periods but could not return to the Warburton because the water sources had dried up in the intervening years.

The desert was named after Alfred Allen Simpson, the president of the South Australian branch of the Royal Geographical Society of Australasia. After the region was surveyed in the late 19th century, the Simpson Desert region was quickly opened to pastoralism. Vast cattle stations were created, but they could run stock only at low densities unless there was rain. Stations like Kalamurina and Macumba were attractive because they offered cattle routes with water sources from Alice Springs south to the Birdsville Track, and on to the markets in Adelaide and beyond. During years of floods or local rainfall, they also offered opportunities for agistment (care and feed for payment) and fattening before sales.

Conservation and Threats

The Simpson Desert has been reasonably well protected in the past by the Simpson Desert Conservation Park/Regional Reserve/National Park and Witjira National Park. In 2006, the Australian Wildlife Conservancy acquired the 2,550-square-mile (6,605-square-kilometer) Kalamurina Sanctuary, which links the conservation areas of the Simpson Desert with the Warburton Creek. This sanctuary allowed the fauna of the Simpson to access the life-giving water and vegetation of the creek’s floodouts without competing with domestic livestock, which had been the case since Europeans began pastoralism in the region.

Despite being covered by a conservation estate, the Simpson still faces severe threats, including exotic species. Early settlers to Australia introduced European rabbits, European red foxes, and feral cats, all of which have been linked to the decimation of Australian native mammals weighing 1.2 ounces (35 grams) to 12 pounds (5.5 kilograms). Noted conservationist Hedley Finlayson conducted fauna surveys of the region in the 1930s and again in the 1950s, and recorded the demise of many species of native mammals. He recorded mass declines of numbats, boodies, brushtail possums, lesser bilbies, and golden bandicoots in the region, and was the last person to record the existence of the desert rat kangaroo near Kalamurina Sanctuary.

Finlayson largely attributed the decline to the effects of introduced predators, in contrast with the activities and effects of such population-trimmers as the dingo, which is considered native, albeit only in the last few thousand years. Camels and rabbits, on the other hand, remove the precious vegetation, causing erosion and lowering the carrying capacity for native herbivores. There is a push within Australia to stop persecuting the dingo because of the protection it affords native wildlife through meso-predator suppression of foxes and cats.

Untapped bores tapping into the Great Artesian Basin also are a problem in the Simpson. Water from the White Bull Bore on Kalamurina Sanctuary comes out of the ground at 207 degrees F (97 degrees C), under enough pressure to drive it 34 miles (55 kilometers) upstream without any pumps. Untapped bores in the Simpson drain the Great Artesian Basin and create biospheres of vegetation damage around artificial water holes and unnatural wetland ecosystems, also providing permanent refuge for species such as the water rat that may not have survived otherwise in such dry places.

Climate change, too, poses threats to the natural balance of the Simpson Desert biome. Temperatures are projected to rise, and evaporation rates will follow suit, making water availability more difficult seasonally in some areas, and causing no-flow periods to be extended when drought conditions prevail year to year. Predicting changes in seasonal rainfall, flooding, aquifer recharge, and surface inundations, however, is far less practicable. What is clear is that plant and animal species will be pushed—depending on the severity of the warming and precipitation scenario—to adapt, migrate, or leave the most harshly arid areas altogether.

Bibliography

Burbidge, A. A. and N. L. McKenzie. “Patterns in the Modern Decline of Western Australia’s Vertebrate Fauna: Causes and Conservation Implications.” Biological Conservation 50 (1989).

Coenraads, R. R. and J. I. Koivula. Geologica: Earth’s Dynamic Forces. Elanora Heights, Australia: Millennium House, 2007.

Dickilometersan, C. R., A. C. Greenville, B. Tamayo, and G. M. Wardle. “Spatial Dynamics of Small Mammals in Central Australian Desert Habitats: The Role of Drought Refugia.” Journal of Mammalogy 92 (2011).

Finlayson, H. H. “On Central Australian Mammals. Part IV—The Distribution and Status of Central Australian Species.” Records of the South Australian Museum 13 (1961).

Letnic, M. and F. Koch. “Are Dingoes a Trophic Regulator in Arid Australia? A Comparison of Mammal Communities on Either Side of the Dingo Fence.” Austral Ecology 35 (2010).

O'Neal, Danielle, Nicholas Ward, and Carli Willis. "Outback in Bloom as Floodwaters Travel Hundreds of Kilometres into Kati Thanda-Lake Eyre." ABC News, 30 July 2022, www.abc.net.au/news/2022-07-31/kati-thanda-lake-eyre-wildflowers-water-outback-in-bloom/101284992. Accessed 1 Sept. 2022.