Department of the Environment, Sport and Territories, 1996
ISBN 0 6422 4427 8
Appendix 1: Australia's biological diversity
As a large island continent with a coastline of some 37 000 kilometres, an area of 771 million hectares, and an Australian Fishing Zone of 894 million hectares, Australia contains a diverse range of biogeographic regions. The arid interior occupies approximately 70 per cent of the continent, with tropical monsoon areas to the north and a Mediterranean and temperate climate to the south. Several mountain regions in the south-east are snow clad in winter and the external territories extend to subantarctic and antarctic regions. Australia's marine habitats are just as diverse, ranging from extensive coral reefs to seagrass plains, giant kelp forests and the sand-bottomed habitats that cover much of the continental shelf.
Australia's biological diversity has great scientific value, and many elements of it are unique. This results, in part, from the tectonic history of the continent and its relative isolation for more than 20 million years following the break-up of the ancient Gondwanan landmass, a period that saw extensive evolutionary divergence of its plants, animals and microorganisms. Australian marsupials have evolved into a great diversity of species filling an extraordinary range of niches, that in other countries are largely occupied by placental mammals.
Of particular significance is the high percentage of Australian species that occur nowhere else (that is, endemic species). Six families of mammals, four of birds, and 14 of flowering plants are endemic – far more families than in any other country. Further, at the species level about 82 per cent of our mammals,7 about 45 per cent of our land birds,8 about 89 per cent of our reptiles, and about 93 per cent of our frogs occur nowhere else.9 These high levels of endemism are not restricted to terrestrial Australia. Of the estimated 600 inshore fish species in the southern temperate zone, about 85 per cent are found only in Australia.10 Australia contains eight endemic families of fish, and more than half of the shark and ray species are confined to Australian waters. The high levels of endemism in the Australian biota are primarily why Australia is considered one of the world's 12 'megadiverse' countries.11
Australia's biota contains a number of groups of very high species richness. Victoria alone has around 270 species of orchid: on the other hand the entire North American continent has only 165 and Europe 116 species.12 Australian deserts have a greater number of species of lizard per locality than do either the Kalahari or American deserts.13 With an estimated 4000 species, Australian ants are also highly diverse compared with elsewhere.14 Britain, for example, has only 41 species of native ants, a number well exceeded by 452-hectare Black Mountain Nature Reserve in Canberra alone, which has more than 100 species.15 There are probably many other groups of invertebrates and microorganisms that exhibit similar species richness but have not yet been adequately studied.
Eucalypts and acacias
The genus Eucalyptus consists of about 900 taxa, with all but thirteen species being endemic; most of the approximately 1070 Australian taxa of Acacia occur nowhere else in the world. Indeed, the omnipresence of eucalypts and acacias characterises Australia's flora. They have diversified into almost every habitat on the continent. Eucalypts range in form from giant forest trees to mallee shrubs and can be found from snowline to shoreline, in deserts and swamps and on floodplains. The River Red Gums have an extraordinarily wide distribution, ranging from south-east Australia through the Red Centre to the north-west. They are a good example of a species complex comprising populations that differ markedly in their genetic makeup.
Components of Australia's biota are of major evolutionary significance. Examples are the Queensland lungfish, which has remained relatively unchanged for over 100 million years, and some species of the relict Gondwanan rainforests of north-east Queensland that have important ancestral links in the history of plant evolution. Nowhere else in the world is there such a concentration of primitive flowering plants. Of the 19 known families of primitive flowering plants, 13 are found in northern Australia. Two of these are found nowhere else.16 Another illustration is Australia's southern marine platform, one of the largest in the world, which has remained stable for at least the last 40 million years and thus provides a unique glimpse of the direct ancestral lineages of many species found there today. Examples of ancient marine animals, or 'living fossils', that occur off the southern marine platform are members of the family Trigoniidae, a bivalve mollusc group widespread 200 million years ago and now reduced to a single genus, Neotrigonia, found only in Australian waters.
Australia's external territories also contain unusual and significant biota. The millions of endemic red crabs on Christmas Island, for example, dominate the forest floor and influence the development of the unique structural characteristics and species composition of the island's vegetation.
For a number of once-widespread marine species now rare or threatened in our region, Australian habitats offer the best chance of survival. Among these species are the Dugong and the Loggerhead turtle.
At a global level, current rates of decline and loss of biological diversity are the highest for at least 60 million years. The declines and losses are continuing. Estimates of probable global losses of species have been as high as 25 per cent for the next 30 years.17
Although the state of Australia's biological diversity may not necessarily reflect global trends, it too has suffered severe declines and extinctions, especially in the past 200 years. There have been fluctuations in rates of decline during this period, but the rates have been greatest in the past 50 years. Despite increased concern and efforts to maintain biological diversity in the last two decades, declines continue and the threat of further extinctions persists.
Dramatic habitat modification and fragmentation have severely affected Australia's native species, and the effect has been compounded by introduced species and other impacts. Twenty mammal, 20 bird and 76 plant species20 are known to have become extinct since European settlement.21 Seventy-seven species of vertebrate animals and 236 species of vascular plants are considered endangered (that is, likely to become extinct if present threats continue), and another 66 species of vertebrates and 652 species of vascular plants are vulnerable (likely to become endangered in the near future).22 Because the trends are similar in all of the better known groups of organisms, it is probable that losses will also have occurred in lesser known groups such as invertebrates, non-vascular plants and microorganisms.
Major vegetation changes
Human activities have been changing Australian ecosystems for at least 50 000 years, but during the past 200 years the pace and extent of change have increased significantly. As a consequence of the processes of economic and social development that were encouraged by all governments following European settlement, about 90 per cent of the native vegetation in the eastern temperate zone has been removed for human habitation, industry and transport or replaced by introduced pastures and crops.18 About 50 per cent of our rainforests have been cleared, and the proportion of Australia covered by forest or woodland has been reduced by more than one-third.19 Extensive clearing and vegetation modification continue to result in severe reduction and fragmentation of the mallee, mulga and brigalow woodlands. Further, with more than 80 per cent of Australia's 18 million people living in urban centres, most of them within 50 kilometres of the coast, land use and population pressures have had substantial impacts on the biological diversity of coastal ecosystems, including mangroves, estuaries and tidal marshes. Freshwater habitats have also suffered in recent decades, as a result of increasing salinity and nutrient levels, other pollutants, land fill or dredging operations, and the impacts of introduced species.
The indicative map below illustrates the major vegetation changes in Australia since 1788.
A map of the extent, type and level of landcover disturbance for the entire continent. In the intensive landuse zone, the coastal strip, clearing for crops and pastures is the principal disturbance. In this zone, the disturbance level is grouped into uncleared (dark green), thinned (brown), cleared (yellow) and indeterminate (blue). For the remaining central core of the continent, the extensive landuse zone, grazing and burning are the principal forms of disturbance. Here, the disturbance level is grouped into slight (light green), substantial (brown), significant (yellow), indeterminate (blue) with salt lakes in black.
This indicative map is a composite of Figures 3.1 & 3.6 of Biodiversity Series, Paper No. 7.
On a regional basis, species declines have been much higher in some areas than in others. The number of endangered plants is highest in the agricultural areas of the south-east and south-west, in the eastern coastal region and in the rainforests of north Queensland. In the deserts, 33 per cent of the mammal species have become extinct23 and 90 per cent of all mammal species weighing between 35 and 5550 grams (that is, from mouse size to small wallaby size) are either extinct or endangered.24
Extinctions and declines in the distribution and abundance of species result in a loss of genetic diversity. Without genetic variability a species is less able to evolve or adapt to changing environments and is probably more vulnerable to new conditions such as climate change or new diseases. Although they may not be classified as threatened nationally, many species are no longer found throughout their former range and may now occur only in reduced numbers. Large marine species such as sharks, Elephant Seals, southern Blue-fin Tuna and whales have dramatically declined in numbers and distribution in historical or recent times, as have some ground-dwelling and ground-foraging birds, a number of frog populations, native fish populations, and many invertebrate species.
On the other hand, large-scale habitat disturbance has in some cases led to increases in both the numbers and range of native species. Among the marsupials, populations of large kangaroos (the Red Kangaroo and the Eastern Grey Kangaroo) have increased substantially in some areas in response to an increase in watering places. Several species of birds, such as the Galah, the Little Corella, and the Sulphur-crested Cockatoo, have increased in abundance in recent times, and others, such as the Striped Honeyeater and the Crested Pigeon, have extended their distributions.
Despite the growth in environmental awareness during the past few decades, much of Australia's biological diversity faces continued threats, both from the effects of past actions and from current activities. Habitat destruction, modification and fragmentation pose the greatest threat to biological diversity. Over-exploitation of species of plants and animals, the impact of introduced species, and the pollution of soil, water and the atmosphere are also serious threats.
A number of forest, fishery, and other wildlife resources have been altered or reduced through exploitation. Extensive grazing of native vegetation communities has reduced the biological diversity of rangelands. As noted by the Ecologically Sustainable Development Working Group on Fisheries, Australia appears to be at or beyond the maximum production achievable in most of its established fisheries and many stocks have already been over-exploited. Harvesting practices can alter entire habitats, especially through environmentally destructive fishing techniques such as trawling or dredging. The number of bottom-dwelling fauna such as sponges and gorgonians has been markedly reduced in some areas where trawl fishing has taken place.
The introduction of alien species may appear to increase species diversity, but in general these species have serious negative effects on native species, including loss of genetic variation, reduction in distribution and abundance, and extinction.
Many introduced or translocated species, which are without predators or disease to control them, have rapidly increased in number and range and have had a devastating impact on other species or native vegetation. Through selection of the seedlings of many trees and shrubs, rabbits inhibit the regeneration of populations of many species. Many native grasses and herbs, chenopods and Acacia-dominated calcareous landscapes will probably disappear if rabbits are not controlled in the first instance. Recent studies have implicated foxes in the disappearance of remnant populations of endangered mammals, and they may be affecting ground-dwelling birds such as the Mallee Fowl. Other introduced species have dramatically reduced the habitat range of native species. For example, habitat competition from goats has resulted in Yellow-footed Rock Wallabies becoming rare in their former range.
Marine organisms introduced either deliberately or by accident may cause significant declines in indigenous species, often species of commercial significance. For instance, the Sydney Rock Oyster is being displaced by the introduced Pacific Oyster. Furthermore, algal and other species introduced in ballast water discharged from ships may adversely affect commercial shellfish and other species.
Twenty-one species of exotic fish are known to have established breeding populations in Australia.25 Lowland rivers have been invaded by Carp, Goldfish, Redfin and Trout. Exotic or translocated fish species may cause the decline or disappearance of native species or distinct genetic stocks through competition or predation, hybridisation or the disturbance of ecosystems. The import of exotic fish has also resulted in the introduction of fish diseases previously unknown in this country.
Introduced species now constitute up to 15 per cent of the Australian flora; the proportion is as high as 31 per cent in Tasmania.26 Plant invasions have predictable consequences. Through competition for limited resources and consequential effects, introduced species reduce native plant and animal diversity and modify the landscape. For example, Bitou Bush is spreading vigorously through a wide range of coastal communities, displacing native species, placing at risk known endangered and endemic flora, and reducing the range of some widespread communities and species.
Pathogens introduced to a region to which they are not indigenous also have adverse effects on biological diversity. Perhaps the best example of this is Phytophthora: up to eight alien species are documented as occurring in temperate forest and shrubland areas. The effect of Phytophthora species in the south of Western Australia has been to reduce the biomass of native flora by up to 90 per cent in some areas.28
The release of pollutants into the environment is both a potential and an actual threat to biological diversity, with severe impacts such as the degradation of freshwater ecosystems or seagrass communities. There are also long-term potential impacts on biological diversity arising from any climate change caused by increases in atmospheric concentrations of greenhouse gases.
The use of chemicals in urban areas and by industry and agriculture has had immense benefits but at times has caused serious pollution. Improved technology has eased but not eliminated the problem and the run-off from industrial plants, urban areas and farms still causes loss of biological diversity and disruption of ecological processes. Aquatic environments are particularly vulnerable to the discharge of nutrients such as phosphates and nitrates in the form of urban, agricultural and industrial effluents; these nutrients contribute to eutrophication and algal blooms, which release toxins that poison organisms such as fish.
Although most of these threats are being dealt with in various ways, dealing with them alone is not sufficient. Biological diversity loss cannot be effectively slowed unless its underlying causes are directly confronted. These causes are extremely complex; they include the size and distribution of the human population, the level of resource consumption, market factors and policies that provide incentives for biological diversity depletion, under-valuation of environmental resources, inappropriate institutions and laws, ignorance about the importance and role of biological diversity, and under-investment in biological diversity conservation.
|Jurisdiction||% of total numbers|
|Australian Capital Territory||28|
|New South Wales||16|
|Lord Howe Island||48|
Source: Humphries et.al. 27