Biodiversity
Theme commentary
Steven Cork, Land & Water Australia and CSIRO
Paul Sattler, Paul Sattler Eco-consulting Pty Ltd
Jason Alexandra, Alexandra and Associates Pty Ltd
prepared for the 2006 Australian State of the Environment Committee, 2006
State of biodiversity
Species, habitats and ecological communities
Australia has one of the highest levels of biological diversity in the world. That diversity exists at a range of scales—landscapes, ecosystems, species and genes—that should all be considered in a state of biodiversity assessment.
Unfortunately, we have imperfect knowledge of the condition and trend of biodiversity at any scale and the ecological implications of this for sustaining Australia’s natural systems and heritage.
Since the commencement of the EPBC Act, there have been 134 species and 10 ecological communities added to the original lists of threatened species and threatened ecological communities . This includes neither transfers to other categories on the list nor species that have been delisted. Changes to these lists are essentially in response to public nominations from parties with an interest in a particular species or ecological community. It is not a systematic assessment of species or ecological communities most at risk. Therefore, these lists cannot be used as an accurate indicator of biodiversity change. New approaches to assessing changes in biodiversity from information in listing processes are worth looking at for future state of the environment reports (Butchart et al 2006). The alignment of listing processes between the Commonwealth and the states and territories is reported in DEH 2006.
A large proportion of Australia’s threatened species occurs within the Murray-Darling Basin, south-west Western Australia, populated coastal parts and in the Tasmanian Midlands: these are regions where intensive development has occurred. Threatened vascular plants and threatened birds are declining across much of the continent. Threatened mammal species are rapidly declining, particularly in arid parts of Western Australia. Threatened reptiles are declining across Australia and threatened amphibians are declining in southeastern Australia South-East Queensland, Brigalow Belt South, and the Wet Tropics bioregions (NLWRA 2002).
An analysis of the two Bird Atlas surveys, 1977–1981 and 1998–2001, showed that 29 species (out of 497 species) had significantly decreased reporting rates over this one 20-year period. Grassland, woodland and ground-nesting guilds were particularly affected (Garnett, Crowley and Barrett 2002; NLWRA 2002, Olsen et al 2006).
Twenty-two species of mammals are extinct in Australia; a further eight species are found only on islands. A further two, possibly three, have become extinct on Christmas Island. Arid and semi-arid parts of Australia have generally lost a high proportion of their mammals (NLWRA 2002).
What these examples show is a continuing serious decline in biodiversity across Australia. This declining trend may be at different rates for various taxa. As bird species are often quite mobile, the full effect of habitat contraction and change in condition has yet to become evident. In contrast, many mammal species have high attrition rates with changes in habitat. The contraction of mammal species and mammal extinction is unparalleled in any other component of Australia’s biodiversity. Significant decline is continuing and further extinctions are likely (NLWRA 2002).
Some bioregions such as the Carnarvon Basin, Jarrah Forest and Channel Country retain a high proportion of species that have significantly contracted from their distributional range and should be a focus for conservation measures.
Conservation effort should also focus on non-threatened species and ecosystems. Of particular value is the conservation of endemic species, that is, species with narrow distributions that could be readily lost with the advent of threatening processes. To aid regional planning, NLWRA (2002) carried out an assessment of endemism for some plant taxa on a bioregional and subregional basis, where the occurrence of species might be related to a particular environment or subject to a specific threat. This assessment has expanded Australia’s knowledge of key areas for the protection of endemic species for the groups studied and should be expanded to all species. This is now feasible with the validation of species records as part of the Australian Virtual Herbarium project (NLWRA 2002).
Declines in biodiversity in freshwater systems, including wetlands and riparian systems, are particularly complicated by low levels of knowledge and understanding. Freshwater biodiversity around the globe is declining more rapidly than any other major group. Alteration of the physical habitat in streams has led to reduced biodiversity. Compared to terrestrial species there are few threatened species listed from inland waters, few nominations for the threatened species list, and the general taxonomic knowledge is also poorer. Other than for a few ‘iconic’ groups—such as fish , frogs and water birds —there is little knowledge or appreciation of the urgency of the situation. The only major group to apparently increase due to river modification is the cyanobacteria (blue-green algae). About one third of river length is impaired to some degree and has lost between 20 per cent and 100 per cent of the aquatic invertebrates that previously lived there. All the available evidence points to reduced numbers of Australian native fish . There is a continued increase in introduced species, including Carp (Cyprinus carpio), Gambusia (Gambusia holbrooki) and Oriental Weatherloach (Misgurnus anguillicaudatus). Australia ranks thirteenth in the world in terms of overall frog biodiversity and twelfth in terms of the number of threatened species. There is an increasing number of sites in Australia in which frogs are no longer found (Tyler 2006).
Four species are listed as extinct under the EPBC Act, some 15 are endangered and another 12 are listed as vulnerable; overall about 20 per cent of species are threatened. Many migratory bird species are endangered or threatened by habitat loss in their native habitats or along the migratory routes.
Severe reductions in wetland extent in Australia have reduced the available habitat as well as the numbers and breeding success of native water birds (Table 6). Climate change has the potential to impact strongly on all species. Wetland and floodplain communities have been degraded across large areas of the intensive land use zone through overgrazing, salinisation, lack of flooding, and the introduction of exotic species. Changes in the flow regimes and ecology of Australian inland waters are favouring the spread of many introduced species.
| State or territory | No. of Sites (C'wealth owned or managed in brackets) | Number of wetlands with threatened water regimes* |
|---|---|---|
| Australian Capital Territory | 13 (0) | 4 |
| New South Wales | 178 (6) | 38 |
| Northern Territory | 33 (4) | 7 |
| Queensland | 181 (8) | 42 |
| South Australia | 69 (1) | 19 |
| Tasmania | 89 (0) | 13 |
| Victoria | 159 (4) | 57 |
| Western Australia | 120 (8) | 51 |
| External Territories | 9 (9) | |
| Total | 851 (40) | 231 |
* Davis et al (2001)
Source: Environment Australia (2001)
Threats to wetlands include change in drainage due to peat moss extraction, walkers, cattle and sheep trampling, channels dug for sheep watering holes, irrigation , sedimentation , water diversion, river regulation, levees, dams , sand weirs, water storage , mining, saltwater intrusion , groundwater extraction , prolonged inundation (causing tree deaths), potentially changed flooding regimes due to clearing for horticulture and mixed farming, siltation through overgrazing, aquifer drawdown caused by water harvesting from the Great Artesian Basin, road and drain construction, tourist and recreational development, altered hydrology to prevent tidal intrusion, road crossing, urban expansion, discharge from sewerage treatment plants , and disposal of saline groundwater. For a further discussion on aquatic biodiversity see the commentaries ‘Inland waters’ and ‘Coasts and oceans’ .
Landscapes and ecosystems
Comprehensive information on the state of ecosystems in Australia was assembled by the NLWRA (2002) using expert opinion. While this is now several years old, no comparable dataset has been prepared or analysed since, and the information collected and the general trends remain pertinent in 2006.
Using the same criteria that were applied to assessing threatened ecological communities under the EPBC Act, the NLWRA (2002) concluded that more than a third of Australia’s 85 bioregions have at least 30 per cent of their ecosystems threatened (endangered and vulnerable). Within extensively developed coastal areas and the Murray-Darling Basin, more than 50 per cent of ecosystems are threatened in most areas (Figure 7).
Note: In some bioregions, the total number of ecosystems has not yet been determined to enable a percentage to be derived; Source: NLWRA
The highest number of threatened ecosystems falls within eucalypt woodlands, which have generally been overlooked in determining conservation priorities in favour of the wet sclerophyll forests of eastern Australia. It is likely that, with improved data and more comprehensive mapping, the number of ecosystems that are considered to be threatened will increase.
Thirty-two threatened ‘ecological communities ’ were listed (at 21 July 2005) under the EPBC Act. Some of these ecological communities incorporate a number of component threatened ecosystems identified at a bioregional level. Some of the states and the Australian Capital Territory have separate legislation for the listing of threatened ecosystems or for specific recognition of threatened ecosystems in vegetation management legislation (see DEH 2006).
Key issues remain: they include the development of recovery plans for listed threatened ecological communities and ecosystems, and the implementation of cooperative management arrangements between levels of government. Definition of ecological communities will continue to be debated because the scientific underpinning is still developing, but a more systematic process of identification, listing and development of cooperative recovery programmes is needed.
Strategic planning of restoration efforts is vitally important to achieve multiple environmental benefits, but some objectives carry formidable challenges. The scale of past deforestation in Australia means that, if a hypothetical target of 30 per cent vegetation was to be re-established, the replanting and safeguarding of regrowth over nine million hectares would be required (NLWRA 2002). In parts of the landscape, much higher levels of revegetation could be required to reduce salinity, and even then amelioration will only occur over long timeframes.
Assessing the changing state of biodiversity at landscape scales requires not only information on the extent of vegetation but also data on its condition as habitat. Approaches to assessing condition are still at experimental stages. An expert opinion assessment of Landscape Heath in Australia (NLWRA 2001) indicated that nearly a third of the intensive land use zone (non-rangelands) has less than 30 per cent remnant vegetation, and the connectivity of remnant vegetation across the landscape has been lost in nearly half of this zone.
In northern Australia, the condition of nationally important wetlands is generally good, but in southern Australia, more than a third of nationally important wetlands continue to decline (NLWRA 2002). The management actions that are required to effect recovery in southern wetlands relate to abating the principal threats of overgrazing, introduced species, pollution, salinity and other changed hydrology. The condition and trend of regionally important wetlands is poorly known. This is significant because these wetlands are often more vulnerable to incremental loss but essential for the protection of regional biodiversity. In some regions, altered flow regimes have resulted in the loss of ninety per cent of floodplain wetlands in the Murray-Darling Basin, 50 per cent of coastal wetlands in New South Wales and 75 per cent of wetlands on the Swan Coastal Plain in south-west Western Australia (Arthington 2002).
In more than two-thirds of Australia, the condition of riparian zones is poor and requires significant management intervention to achieve recovery. Riparian systems in more than three quarters of Australia are continuing to degrade. This has serious ramifications for the protection of both terrestrial and aquatic biodiversity (NLWRA 2002); however, analysis of the extent of riparian vegetation shows that the extent of riparian vegetation has stabilised over the past few years (ERIN 2005).
Economic challenges faced by individual landholders, such as low profitability or high accumulated debt, often present major barriers to the adoption of management regimes that protect remnant vegetation and riparian corridors (Green and MacLeod 2002). This is a major issue that needs to be addressed in designing specific regional strategies for biodiversity conservation. Such strategies will necessarily involve a number of measure , ranging from stewardship incentives, to structural adjustment, to accepting degraded land and stream frontages.