Carpentaria tropical savanna

• Category: Grassland, Tundra, and Human Biomes.
• Geographic Location: Australia.
• Summary: This semi-arid savanna has proven resilient over the millennia but is threatened by ranching and global warming.

The Carpentaria Tropical Savanna biome stretches inland from the Gulf of Carpentaria on the north-central coastal region of Australia. It comprises portions of both the Northern Territory and the state of Queensland. The savanna lies in a band of up to 125 to 280 miles (200 to 450 kilometers) that encompasses the shoreline of the gulf up to rolling hill areas, extending east to west some 745 miles (1,200 kilometers). Tropical and subtropical grasslands, savanna proper, and shrublands are all contained within the biome.

Mangroves and grasslands along the Gulf transition to open woodlands of eucalyptus trees with an understory of grasses in the genera Spinifex and Triodia. Along streams, the river red gum (Eucalyptus camaldulensis) is prominent; small stands of rainforest are also seen, especially in the rocky uplands. Rainfall here is mainly a summer phenomenon; the average range is 16–48 inches (40–120 centimeters) annually, and cyclones account for a not insubstantial part of that. The driest areas inland may receive only 8 inches (20 centimeters) of rain. Temperatures at the high end reach 97–102F (36–39C).

The grasslands here, among the largest expanses on the continent of Australia, have long supported grazing and agriculture. While a boon to the settler economy, grazing is now a considerable threat to habitats in the Carpentaria, as invasive grasses have upset the balance of some local biota. Likewise, various nonnative animal species of donkey, cat, goat, and pig have become feral, engendering new inputs while stressing native grasses.

Morning Glory Tour

Along the northern coastline, cool Pacific Ocean winds breach inward over the land until they collide with a thick blanket of warm, humid air. Upon this U-shaped inlet, a rare type of cloud forms, dubbed the Morning Glory. This only happens in spring, typically on a 90F (32C) day. The last rain was not enough to satiate the cracked clay ground; the soils are hardened with dry roots that have been baking in the sun for the past seven months. Relentless, the sun evaporates the moisture from the ground, giving rise to the horizontal tubelike Morning Glory cloud.

The great wavelike cloud rolls from Cape York Peninsula, entering over the Gulf of Carpentaria and spans across the coastal shores where white and Aboriginal fishermen mingle. The indigenous inhabitants own or lease nearly one-third of the land within this region. In the wetlands along the gulf, dugongs share the shallows with migratory wading birds. Terrestrial birds here include the ubiquitous king quail (Coturnix chinensis colletti) and long-tailed finch (Poephila acuticauda). A rarely seen, endangered avian species that haunts the biome is the red goshawk (Erythrotriorchis radiatus).

The Morning Glory cloud now rolls above patches of wetlands and seasonal ponds shaded by mangroves. Edging southwestward, the cloud soars over yellow plains of hummock grass, open eucalyptus forests, and acacia trees. The plains are interspersed by plateaus and giant rock towers. They are horizontally stratified, exposing the years in which sediments have been washed along the floodplain, deposited by streams and rivers, and compressed with yet another year of weather and new sand.

Soils vary in color from yellow and red to shades of brown. Laterite soils are embedded with heavy metals, providing the vegetation above with meager nutrition. The mining pits found in the area give testament to the metals hidden deep within the soils that have yielded zinc, lead, and silver.

The land appears dry and desolate, with the exception of a few cattle. In taking a closer look though, exotic and native organisms are interacting with one another on a daily basis. A cane toad (Bufo marinus) hides under the brush of a prickly acacia tree (Acacia nilotica). Both the toad and the tree are exotic species, brought to the continent for practical intentions. They have adapted to the region, competing with resources of other native animals; various native reptiles and amphibians have declined with the rise of cane toad populations. Efforts to control the spread of acacia trees have been ongoing since the 1980s, but with limited success due to its invasive nature.

Empires of termites rise and fall within dirt mounds, some of which are taller than people. Almost four hundred species of termites are found in Australia, a mix of both native and exotic species. Under the ground, rodents and mammals have created hideouts. The endangered northern quoll (Dasyurus hallucatus) sleeps away the afternoon keeping cool in its den while snakes bask in the sun. Meanwhile, the kangaroo and wallaby can be found grazing on grass.

Finally, the Morning Glory cloud approaches eagerly waiting hang gliders in an open, rolling field. They take off and drift upward toward the horizontal tunnel cloud. As the afternoon presses on, the hang gliders ride out the cloud with great skill until it dissipates over the horizon.

Threats and Conservation

The expansion of cattle ranching is a growing concern in maintaining a balance with both fire and the native species. Exotic feed grasses have overtaken the habitat of many Australian plants. And when ranchers occupy a land with too many cattle, the fire regime changes, with more frequent but less intense fires. It is unclear what long-term effect this has on habitat and regrowth.

Strategies for fire management in this region incorporate both modern technology through predictive modeling and traditional Indigenous knowledge. Some scientists, for example, have calculated that if ranch owners clear pastures later in the dry season, they can reduce the amount of carbon released into the atmosphere through fire. Aboriginals, for their part, are cautious to invite any changes to a system that has worked well for centuries.

Climate change has intensified droughts, which had already occurred in the region once every twenty years or so. Wildfires are more frequent than they were in the past. The shallow soils of this biome, although in part regenerated by fire, are not helped by the trampling of cattle nor the disruption of invasive species. Additional stress in the form of longer, hotter droughts coupled with potentially stronger cyclones and the erosion from higher storm surges threatens viable habitats. The overall flat nature of the land here is another characteristic that makes the biome more vulnerable, as such a surface is not favorable for capturing rainfall, making inland erosion a danger and doing less to provide for habitat niches than a more topologically diverse landscape could.

Across the savanna region, there is evidence that small mammals are already under high stress; global warming effects are not likely to reverse this trend. On the other hand, studies of the tropical savanna bird species here indicate that, while the habitat range for some species might decrease, territorial opportunities for many of the migratory species may increase with global warming.

Reserve areas are patchy at best in the Carpentaria tropical savanna. The Boodjamulla National Park, which spans about 1,500 square miles (3,880 square kilometers), is located near the inland extreme of the savanna and has many waterfalls and limestone and sandstone gorges. Chillagoe-Mungana Caves National Park protects another 14 square miles (36 square kilometers), characterized by such plants as kurrajong or bottle tree (genus Brachychiton) and the coral tree (Erythrina variegata).

Bibliography

Booth, Carol and Barry Traill. Conservation of Australia's Outback Wilderness. The Pew Environment Group and The Nature Conservancy, 2008.

Comben, David F., et al. "Genetic Identity of Australian Prickly Acacia (Vachellia Nilotica, Fabales: Mimosoideae) – Assessing the Target for Biological Control." Biological Control, vol. 155, 2021. doi.org/10.1016/j.biocontrol.2021.104540. Accessed 11 Dec. 2024.

Grice, Tony and Shane Campbell. Weeds in the Tropical Savannas. Queensland Department of Natural Resources and Mines, 2001.

Morton, Adam. "Australian Scientists Warn Urgent Action Needed to Save 19 'Collapsing' Ecosystems." The Guardian, 25 Feb. 2021, www.theguardian.com/environment/2021/feb/26/australian-scientists-warn-urgent-action-needed-to-save-19-collapsing-ecosystems. Accessed 11 Dec. 2024.

Native Vegetation Management—A Needs Analysis of Regional Service Delivery in Northern Territory—Savanna. Greening Australia, 1 June. 2003. Territory Stories, hdl.handle.net/10070/671484. Accessed 11 Dec. 2024.

Olson, David. “Carpentaria Tropical Savanna.” One Earth, 23 Sept. 2022, www.oneearth.org/ecoregions/carpentaria-tropical-savanna/. Accessed 11 Dec. 2024.