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Biological diversity, or 'biodiversity', is the variety of all life forms --- the different plants, animals and micro-organisms, the genes they contain and the ecosystems of which they form a part. Biodiversity is constantly changing; it is increased by genetic change and evolutionary processes and reduced by processes such as habitat degradation, population decline, invasion and extinction. Biodiversity covers terrestrial, marine and other aquatic environments and is considered at three interrelated and interdependent levels:
Australia is identified as one of 17 megadiverse countries. These countries have an exceptional total number of species, and a high degree of endemic species found exclusively in that country. As a consequence of Australia's size, relative age and isolation, its flora and fauna have evolved to become a globally significant centre of endemism, with over 80% of our mammals, flowering plants, reptiles, frogs, fungi, molluscs and insects known only to occur in Australia (Williams et al. 2001).
Estimates of the total number of species in Australia vary considerably, from about 500,000 to in excess of 10 million (Horwitz, Recher & Majer 1999). Table 14.14 presents the most recent estimates of the number of species currently known in Australia and the percentage of endemic species for each taxa. Only a few groups of species are thought to be entirely known, reflecting the limited state of our knowledge of Australia's biodiversity, particularly with respect to invertebrates and micro-organisms.
Many terrestrial and marine regions within Australia are globally significant centres of biodiversity (Williams et al. 2001). The south-west Western Australia region supports the eighth highest number of endemic vascular plant species in any one region (about 2,830 species), and contains over one-third of Australia's plant species. The Great Barrier Reef contains about 2,000 reef fish and 500 coral species, the highest concentration of the world's fish and coral species. The rainforests in the Wet Tropics of northern Queensland are also internationally identified as major centres of biodiversity.
Ecosystems are a dynamic complex of plant, animal and micro-organism communities which, together with the non-living environment, interact to maintain a functional unit (Commonwealth of Australia 1996). Ecosystems contribute to the maintenance of water cycles, photosynthesis, gene flow, soil production and protection, storage and cycling of nutrients, regulation of climate and carbon sequestration. Ecosystem diversity is defined by the variety of these processes, habitats and biotic communities, and is generally considered in terms of distinct vegetation types, or marine and freshwater habitats. On the basis of vegetation alone, Australia has a wide range of ecosystem types ranging from rainforests, eucalypt forests and woodlands, acacia shrublands and mallee to heath, mangroves and grasslands (see the section Extent and clearing of native vegetation).
For the purposes of analysing Australian ecosystems at the continental scale, the Interim Biogeographic Regionalisation of Australia (IBRA) (Thackway & Cresswell 1995) and the Interim Marine and Coastal Regionalisation for Australia (IMCRA) (IMCRA Technical Group 1998) have been developed. In Australia, IBRA and IMCRA have identified 85 terrestrial bioregions and 60 marine bioregions representing the major environmental units in Australia. These provide a framework for conservation planning and sustainable resource management within a bioregional context.
Conservation of biodiversity
The loss of biodiversity is considered one of the most serious environmental problems in Australia. The clearance of native vegetation is a significant threat to terrestrial biodiversity (see the section Extent and clearing of native vegetation). Other key threats to biodiversity include invasive species (i.e. pests and weeds; see the section Invasive species), dryland salinity, pollution, nutrient loading and sedimentation of waterways and coastal areas, altered hydrological and fire regimes, and climate change. These processes pose a major threat to sustainable management of our ecosystems and the environment, as well as to the social and economic values of biodiversity.
The Commonwealth administers biodiversity conservation through the Environment Protection and Biodiversity Conservation Act 1999 (Cwlth) (EPBC Act 1999). This Act provides for: identification and listing of threatened species and threatened ecological communities; development of recovery plans for listed species and ecological communities; recognition of key threatening processes; and where appropriate, reducing these processes through threat abatement plans. In August 2002, 116 flora and fauna species were listed as extinct, and 1,488 species and 27 ecological communities were listed as threatened under the EPBC Act (table 14.15). At that time, 140 recovery plans had been adopted covering 183 of these listed species.
As a signatory to the International Convention on Biological Diversity, Australia is required to establish a system of protected areas. These areas are dedicated to the protection and maintenance of biological diversity and of natural and associated cultural resources. The EPBC Act (1999) is the principal Commonwealth legislation for establishing and managing protected areas, which are developed according to the National Strategy for the Conservation of Australia's Biological Diversity (Commonwealth of Australia 1996). The strategy calls for a Commonwealth, state and territory cooperative program to ensure that Australia's terrestrial and marine protected area systems are comprehensive, adequate and representative.
In 2000, there were 5,251 protected areas in Australia, occupying 61.4 million hectares and accounting for 7.8% of the total land area. Of the six international IUCN (World Conservation Union) management categories, national parks (39%) and nature reserves (31%) comprise the largest proportion of Australia's total protected area (table 14.16). At present, the conservation reserve system does not represent all ecosystems equally, with about 40% of IBRA regions having less than 5% of their land represented in protected areas. Arid and semi-arid environments, native grasslands and wetlands are particularly poorly represented. Given the small proportion of many landscapes in protected areas, conservation outside formal reserves is an important mechanism for biodiversity conservation and requires the involvement of farmers, businesses, conservation groups, resource users, Indigenous peoples and the wider community.