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Austraila's desert heart - red but not dead
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From space, the colour of Australia is of heat - reddish in colour, dusted with a northern, eastern and southern rim of green To emphasise this impression, much of the central and western area looks as if it is blistered with great white patches of salt lakes. The tourist industry has called this hot centre The Red Centre, sometimes The Dead Heart. But NO! An important characteristic of living things, is that their genetic processes, tested by the environmental conditions forming their birth habitat, allow the strengths of the animal’s bank of genes to fit their habitat. If the fit is not successful, then the animal will die. If the fit is successful, then the animal survives and will breed others with similar success.
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| | So no matter how harsh and difficult a habitat may be, over time each place builds up populations of plants and animals that through this process of natural selection, adapt to the desert conditions . This adaptation may mean the shape or form of the organism has changed. For example the scaley skin of the a Thorny Devil lizard channels even tiny rain drops and puddle water by way of capillary action between its scales, running the water to the lizard’s mouth.
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Australian desert is far from being just a vast area of sand. Many low ranges break up this pattern. Some of these, in particular the Macdonnells and the Flinders as well as a number of high areas in the Pilbara are high enough to increase local rainfall that in its runoff has cut great canyons, valleys and gorges. Numerous small, low tablelands or mesas further diversify the desert systems. Flying to Darwin, Alice Springs or Broome across Australia, the vista ranges from wonderful skeletal rock structures, clear of all vegetation to blue-green mulga scrub, the sinuous windings of ancient stream beds going nowhere but accented with dark outlining by deeply rooted River Gums. Then there are the endless ridges of sand speckled with spinifex hummocks like some endless Aboriginal canvas. Overprinting all landscapes are the massive scars of recent and old wild fires.
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| Uluru, symbol of Central Australia is all that remains of an ancient mountain range after 300 million years of erosion and over many climatic changes. Runoff from this great sandstone ‘roof’ forms a number of waterholes and ‘green’ country around its base that provide food and water resources for wildlife and humans.
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| | Red sands of Central Australia are heaped into large dunes by directional winds. Here the westerly wind is shifting sand grains into tiny dunes, the ripples, that themselves move to the dune crest and tumble down the opposite slopes that are usually very steep. So the dune moves on. This dune was once stabilised by spinifex and mulga - wildfire has burnt off the vegetation so the dune moves on.
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| | Over perhaps fifteen million years, rivers draining the western Macdonnells ran onto lower country among the desert dunes. The water evaporated after each flood, leaving behind the salts that were dissolved in the river water. Thousands of floodings built up the residue of salt forming the salt lakes.
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| The large white dunes along the eastern shores of lake Mungo are derived from the sandy clay bed of the dry lake, swept up by the westerly winds. Note the steep slopes on the eastern side of the dunes in this picture. The prevailing winds here move from right to left.
Below: Wave upon wave of dunes stabilised by mulga, other shrubs and spinifex grass, seen from a higher crest on the way to Chambers Pillar.
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| Hummocks of daisy bush on the dune with mulga growing in the swales or flats between the dunes.
The cores of the dunes hold water long after rains.
This moisture is used by many specialised plants of the desert – Desert Oaks (Casuarina), Grevilleas, Mulga, Witchetty Bush (or Acacia) and Emu Bushes.
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| Ghost Gums struggle to survive on the rugged sandstone ridges of Kings Canyon National Park. Beneath a waterfall at the head of the gully below, is a permanent waterhole (fed by Kathleen Springs) that provides water for Euros, Red Kangaroos, thousands of Galahs, Corellas, Pink Cockatoos, Budgerigars and Spinifex Pigeons. The trees by the creek are Desert Bloodwoods.
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| The damp, cooler, shaded canyons of the Central Australian desert are the final sanctuaries for some plants and animals that the desertification of the Centre has driven to extinction elsewhere. This cycad (Macrozamia macdonnellensis) living in the Kings Canyon or at the entrance to Palm Valley is a case in point, as are the Red Cabbage Tree Palms of Palm Valley – relics of earlier, more humid times.
By contrast, many plants have gradually adapted via natural selection to be able to survive and even thrive in the harsh heat and aridity typical of the deserts.
The Mulga Scrub community shown below, at Mutawintji, in a very healthy condition.
These acacias are wonderfully adapted for aridity.
They have both shallow wide-spreading roots to tap light showers and deep roots to sustain them during droughts; prolific seed producers with seed protected by very tough skins that still survive over 100 years in the ground; leaves that are covered with very protective layer of surface cells and coloured pale bluish-green, reflecting heat and strong light.
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| Below: The Red Kangaroo male is a symbol of arid and semi-arid plain country that is extremely mobile particularly when local conditions dry up water supplies – water is the principal limiting factor in their ecology. When pastoralists built water supplies to sustain their stock, they also allowed kangaroo populations to explode causing the 'roo plagues' of the ‘50s – ‘70s.
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| Red Kangaroos also have the remarkable breeding process, delayed implantation, that allows females to carry a living blastocyst on the uterus wall for over 300 days without development. So they carry a spare joey for long periods until the weather changes and green feed appears, without having to find a male to fertilise her egg. A bullet in the barrel so to speak!
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| The Perenti, this one’s nest being under a surface layer of arid zone limestone hardpan at Mt Connor, represents the second largest lizard in the world after the Komodo Dragon.
Many of the desert lizards live underground to escape desert heat and dehydration.
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| The Pink Cockatoos were until recently known as Major Mitchell’s Cockatoos as he was the discoverer and who produced the spectacular portrait of it for his journal in 1836.
These days this magnificent bird’s populations have increased living on the masses of the weed, Paddy Melons, when not attacking irrigation crops.
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| With so much dry, woody and waxy vegetation, all adaptations to counteract desert environmental conditions, fire burns freely once ignited.
Here, a spinifex fire, lit by carelessness, burned a large area and three weeks later, sprang to life again as a smouldering mulga root came close to an unburned spinifex, igniting the area again.
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| | From the air, the fire patterns can be interpreted like huge splashes that run and widen during daylight and shrink, narrowing down during the cool, quiet evenings, to take off again as day breaks and becomes warmer. Most rain drops in heavy bursts as storms wander across the country. Such falls may lay a chain of moisture driven ‘green-pick’ lanes across the desert.
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| Wildlife, particularly birds, follow such lanes of food and water that encourage breeding. Other herbivores such as the red Kangaroo will also follow such feed and the green feed triggers off the secretion of breeding hormones in the female kangaroos.
The desert vegetation responds rapidly to rainfall. Sturt's Desert Pea is a good example,
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| Storms in the desert often cause flash floods to move rapidly down creeks because the baked soils take time to allow water to soak in. They are frequently hydrophobic causing heavy runoff.
Here the edge of a flash flood of super-muddy water is reaching 30 Km from its storm source, Broken Hill way.
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| Desert country to marginal country for pastoral industry.
Many stations are only able to sell cattle one year in every four. For example ‘Curtin Springs’ Station, last before Uluru, runs 7000 head on 400,000 hectares. Cost per head is very high and the damage done by stock on those desert ecosystems is disastrous.
By comparison, income per manager generated by tourism in the Centre per hectare of that country is 10 – 20 times and much higher with very little comparable damage.
Curtin Springs’ survives as a cattle station because it also runs a roadhouse on the Lasseter Highway, selling services to tourists. Photos and text by Allan Fox February 2009
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