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Soils, Fauna and Flora

soils, fauna and flora

Soils

All soil types are found in the continent, but poor and mediocre soils predominate, with low organic content. Notwithstanding this, and the fact that large areas of the interior are desert or at best suitable only for light grazing of sheep, soil resources are a significant factor in the Australian economy. Agricultural products constitute upwards of 20 per cent of export earnings today, and in the past dominated exports. Phosphate additives have been used extensively as soil fertilizers for many years; large areas of marginal land have been made more productive by the use of trace elements, such as zinc, copper, and manganese, and some new lands have been opened up to production. However, since the 1970s there has been growing concern about the side-effects of phosphate use. These include soil acidification, and the periodic outbreaks of toxic blue-green algal blooms in the vital Murray-Darling river system, fed by the phosphate-rich run-off from fertilized soils. Wind erosion and in some areas overgrazing in the semi-arid pastoral and agricultural regions, and water erosion in the wetter, deforested south-eastern region are major problems. 

Concern over such problems has led to the growth of a grassroots "Landcare" movement, which has won considerable official support; the federal government has declared the 1990s to be the decade of Landcare. The ecological and economic threats of soil erosion, soil and water salinization, and soil acidification are being countered by technical programmes, scientific research, education, and measures such as restrictions on grazing and reforestation programmes. 

Plants
Australia has a distinctive flora, comprising some 22,000 species of plants. More than 90 per cent are indigenous, and many species are not found elsewhere. Predominantly evergreen, vegetation ranges from the dense bushland and eucalyptus forests of the coast to mulga and mallee scrub and saltbush of the inland plains. Australian plant life is distributed in three main zones. The Tropical Zone runs along the northern margins of the continent and half way down the eastern coast. The Temperate Zone covers the south-eastern coastal area, including Tasmania, and runs up the eastern coast to meet the Tropical Zone. The Eremian Zone occupies the whole of the arid centre and west of the continent. 

The Tropical Zone, with its monsoonal climate and high temperatures, is heavily forested, mainly with deciduous trees. Along the north-east coast of Queensland, including the Cape York Peninsula, there are rainforests. Palms, ferns, and vines grow prolifically among the oaks, ash, cedar, brush box, and beeches. Mangroves line the mud flats and inlets of the low-lying northern coastline. The crimson waratah, golden-red banksias, and scarlet firewheel tree add colour to northern forests. Further inland there is savannah with low trees, mainly of the distinctive sclerophyll (hard-leaved species) which are characteristic of much indigenous flora. Many of the species of plant found in the Tropical Zone are also found in the Malay archipelago to the north-east. 

The temperate zone is characterized by sclerophyll, temperate, and savannah woodlands, by mallees, scrub, and sclerophyll heath, by temperate rainforests, and by alpine vegetation in the Australian Alps and the mountains of Tasmania. More than in the Tropical Zone, the vegetation is typically "Australian". Along the eastern coast and into Tasmania there are stands of pine. Largely introduced, these pines rank second only to the eucalyptus in terms of economic importance; the Huon and King William pines are particularly valuable for their timber. However, the Huon pine is now considered rare and is largely protected. 

In the forest regions of the warm, well-watered south-eastern and south-western sectors, eucalyptus predominates; more than 500 species are found, some reaching a height of 91 m (300 ft). The south-western coast is particularly noted for the richness of its plant life. The mountain ash, blue gums, and woolly butts of the south-east mingle with undergrowth of wattles and tree ferns. Tasmania is noted for its southern beech forests and for its links with the flora of New Zealand. 

In the Eremian Zone there are semi-arid shrub savannahs, shrub steppes, semi-arid grasslands, and sclerophyll grasslands, as well as large areas virtually devoid of vegetation. The vegetation is adapted to the arid conditions, and acacias tend to displace eucalyptus, although the jarrah and karri species of eucalyptus, which yield timber valued for hardness and durability are peculiar to Western Australia. So too are several species of grass tree. The wild flowers which appear after rain are varied and spectacular. In the less dense regions of the interior slopes grow red and green kangaroo paws, scented Boronia, waxflowers, bottle brush, and smaller species of eucalyptus, such as the stringbark, red gum, and ironbark. 

There are more than 500 species of acacia which are indigenous to Australia; the scented flower of one acacia, the golden wattle, has been chosen as the national flower of Australia and appears on the official coat of arms. In the interior characteristic plants are saltbush and spinifex grass, which provide fodder for sheep, and mallee and mulga shrubs. 

The most valuable indigenous fodder grasses, including flinders grass, are found in Queensland and northern New South Wales. During occasional seasonal floodings, rapid and luxuriant growth of native grasses and desert wild flowers occurs, and water lilies dot the streams and lagoons. 

As well as the native flora, Australia also has some 2,000 introduced species of plants. Most have been associated with the development of agriculture and grazing, or with the establishment of large plantations of commercial softwoods. Although Australia is rich in plant species, the area they cover has been hugely reduced since the arrival of the first European settlers in 1788. At that time it is estimated that up to one-quarter of the country may have been covered by forests, savannah woodlands, and scrub. However, only a small proportion had commercial potential, and in the subsequent 200 years much of the indigenous flora was cleared to make way for agriculture and settlement. According to rough estimates produced by government scientists in the late 1980s, loss of indigenous cover ranges from more than two-thirds in Victoria to around one-third in Western Australia; only in the Northern Territory has clearance been negligible. 

The result has been not only an increase in erosional problems, but also the extinction of 83 known indigenous plant species. There are, in addition, 840 known species threatened with extinction. The spread of weeds and other aggressive introduced plants into areas of original vegetation is also a serious environmental problem. Australia�s wildlife has been detrimentally affected by the loss of habitat, which has pushed a number of species to the verge of extinction (see Animals below). However, since the 1980s there has been a considerable increase in public awareness of the need for conservation and pressure to contain further loss of natural vegetation�strongly resisted at times by some economic interests. 

Fauna & Flora

Australia is thought to have up to 300,000 different species of animal life, of which only about 100,000 have been described. There are some 280 known species of mammals, more than 700 species of birds, 380 species of reptiles, more than 120 species of frogs, and almost 200 species of freshwater fish; the remainder are invertebrates. The fauna of Australia is distinctive, deriving mainly from the time when the continent formed part of Gondwanaland. It has most in common with the wildlife of New Guinea, which falls within the Australian faunal zone, and with that of South Africa, which also formed part of Gondwanaland. Many species are unique to Australia, however, reflecting its long isolation from other land masses. They include seven families of mammals, as well as four families of birds comprising about 70 per cent of known species. It is also estimated that about 88 per cent of reptile species and 94 per cent of frog species are unique to the continent. 

The Gondwanan origins of Australia�s fauna are most striking among the mammals because of the absence of representatives of most of the orders found on other continents. The world�s only egg-laying mammals, the primitive monotremes�the platypus and echidna (which is also found in New Guinea)�are Gondwanan. The platypus, a zoological curiosity, is an aquatic, furred mammal with a bill like that of a duck and with poisonous spurs. It lives in the streams of south-eastern Australia. The echidna is also known as the spiny anteater. 

The Platypus

The most characteristic native mammals are marsupials, the young of which are nourished in an external marsupium, or abdominal pouch. Although also found in South America, marsupials in Australia have evolved to virtually all mammalian niches. The best-known Australian marsupial is the kangaroo, of which there  are about 50 species found in both the Temperate and Tropical Zones. The kangaroo is vegetarian and can be tamed. The large red or grey kangaroo may stand as high as 2.1 m (7 ft) and can leap 9 m (30 ft). Originally a creature of the forests and semi-arid shrublands, it is one of the few native animals to have benefited from the extension of pastureland. Numbers have exploded, and hunting is used as a control measure. The wallaby, kangaroo rat, and tree kangaroo are smaller members of the kangaroo family. The phalangers are herbivorous marsupials that live in trees; they include the possum and the koala. Feeding only on the leaves of certain species of eucalyptus, the koala has been endangered by loss of habitat and is protected throughout Australia. Other well-known marsupials are the burrowing wombat, bandicoot, and pouched mouse. Marsupial carnivores, the native cat, the tiger cat, and the Tasmanian devil are found only on the island of Tasmania. The Tasmanian tiger, or thylacine, a sheep-killer, became extinct in the 1930s. 

The only native placental mammals�rodents, bats, and the dingo, or warrigal�are Asian in origin, entering Australia by island hopping or accidental drifting. The Aborigines, however, probably introduced the dingo, a dog-like night hunter and sheep-killer; it does not bark, but howls dismally. 

The continent�s reptiles include two species of crocodiles, the smaller of which is found in inland fresh waters. The larger, salt-water saurian crocodile has been known to eat people and is found in the northern coastal swamps and estuaries; it reaches 6 m (20 ft) in length. The many species of lizards include the gecko, skink, and the giant goanna. As many as 100 species of venomous snakes are found in Australia. The most dangerous are the taipan of the far north, the death adder, the smooth snake, and the brown snake. Other venomous species include the tiger snake of southern Australia, the copperhead, and the blacksnake. 

The waters surrounding Australia support a wide variety of fish and aquatic mammals. Several species of whales are found in southern waters, and seals inhabit parts of the southern coast, the islands in Bass Strait, and Tasmania. The northern waters supply dugong, trepang, trochus, and pearl shell. Edible fish and shellfish are abundant, and the oyster, abalone, and crayfish of the warmer southern waters have been exploited commercially. Australian waters contain some 70 species of shark, several of which are dangerous to humans. The Queensland lungfish is among the most ancient Australian animal species, its evolution pre-dating the formation of Gondawanaland. Sometimes called a "living fossil", it is a fish that breathes with a single lung instead of gills. 

Pre-Gondwanan species are also well represented among the invertebrates, including some insects, spiders, and earthworms. Most insect types are represented in Australia, including flies, beetles, butterflies, bees, and ants. The giant termites of northern Australia build huge, hill-like nests up to 6 m (20 ft) in height. Australia has earthworms in abundance, including the giant earthworms of Victoria, which range from 0.9 to 3.7 m (3 to 12 ft) in length, the longest in the world. Many of Australia�s spiders are poisonous; the funnel-web and red-back spiders are the best known. 

Australia�s birds range from primitive types, such as the giant, flightless emu and cassowary, to highly developed species. The fan-tailed lyrebird has great powers of mimicry. The male bowerbird builds intricate and decorative playgrounds to attract females. The kookaburra, or laughing jackass, is noted for its raucous laughter. Many varieties of cockatoos and parrots are found; the budgerigar is a favourite of bird fanciers. The white cockatoo, a clever mimic, is more common than the black cockatoo. Black swans, spoonbills, herons, and ducks frequent inland waters. Smaller birds include wrens, finches, titmice, larks, and swallows. Gulls, terns, gannets, muttonbirds, albatrosses, and penguins are the most common seabirds. The muttonbird, found mainly on the islands of Bass Strait, is valued for its flesh. 

 

The future of many native species is a matter of growing concern. In all, 20 species of mammals and 16 bird species are known to have become extinct since European settlement. Another 15 species of birds and 38 species of mammals are endangered or vulnerable. They have been put at risk by the clearance of their habitat or by the introduction of foreign species, which compete for food with native species, destroy their habitat, or prey upon them. The main culprits include rabbits, foxes, feral cats, pigs, sheep, goats, cattle, horses, camels, and the Asian water buffalo. 

Probably the most destructive has been the European rabbit. Rabbits accompanied the First Fleet to Australia in 1788, but their modern introduction is normally dated to 1859, when Thomas Austin shipped in 24 wild rabbits for hunting, and released them on his property near Geelong, Victoria. In Australia�s favourable environment, and with few native predators, the rabbit population quickly reached plague proportions; in the early 20th century the rabbit population was estimated at some 500 million. The virus myxomatosis, which kills rabbits, was deliberately introduced in 1951 as a control measure. It was effective for about 20 years, but the rabbits began to gain immunity and their numbers rapidly recovered; today the rabbit population is estimated at 300 million. In addition to destroying the habitat of native species, they also cause soil erosion and huge damage to commercial rangelands and crops. Foxes and cats have also been targeted for biological control programmes and regional eradication schemes. In the monsoonal areas of northern Australia there has been a large increase in the number of water buffalo. Their grazing is causing soil erosion and they are disrupting delicate swamp habitats. 

The extinction of species is not something that has occurred solely since the arrival of Europeans, however. Australia was once home to a number of outsize animals, the megafauna. They included the giant wombat and kangaroo, the marsupial lion, and giant flightless birds. They became extinct over a period of up to 19,000 years, beginning some 27,000 years ago. Aboriginal hunting and burning of vegetation to encourage the growth of preferred plant species may have played a part in their demise. However, climatic changes between 22,000 and 18,000 years ago, when the deserts reached their maximum extent and the weather was cold, are  considered to be equally, if not more, important causes of their extinction.

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