Landscape Health In Australia
A rapid assessment of the relative condition of Australia's bioregions and subregions
Gethin Morgan
Environment Australia, 2000
ISBN 0 642 37119 9
Overview of Australia's Landscape Health
Australia's 354 IBRA* subregions are distinctive landscapes with characteristic patterns of landforms, soils and vegetation. They provide a sound framework for assessing the relative impacts of land use at a continental scale (e.g. in the Brigalow Belt bioregion, the forested sandstones of the Carnarvon Ranges can be assessed separately from the adjacent clay plains of the Arcadia Valley; the Simpson-Strzelecki bioregion is divided into dune fields and the periodically flooded terminal wetlands of Cooper Creek).
Clearing, habitat fragmentation and ecosystem loss
Clearing of native vegetation and the accumulating impacts of past clearing continue to be the major cause of landscape change in intensively used bioregions.
- 57 subregions have less than 30% of the original extent of native vegetation remaining.
Recent work has show that loss of species accelerated greatly when less than 30% of native vegetation remains (James & Saunders 2001).
- Connectivity between native vegetation remnants has broken down in 88 subregions.
Even where the total extent of remnant vegetation cover within a subregion may appear relatively high, the level of vegetation fragmentation may still undermine the ecological health of the landscape.
- 40 subregions where between 30% and 50% of native vegetation remains, have lost most of the connectivity between remnant areas of native vegetation. Clearing is continuing in most of these.
- 39 subregions have more than 70% of their component ecosystems threatened.
At the scale of this assessment, clearing is negligible within the extensive use zone but grazing pressures are widespread.
- 50 subregions out of 172 have more than 70% of their area grazed.
- 25 subregions have more than 90% of their area grazed.
- 39 subregions have little or no grazing.
Conservation reserves
The protection of biodiversity through the reservation of significant areas is an important means of conserving biodiversity. Nationally the level of representation of subregional landscapes within conservation reserves is low.
- 175 subregions have less than 2% of their area in conservation reserves; 33 of these have less than 30% of native vegetation remaining.
- 91 subregions have more than 10% of their area in conservation reserves.
Dryland salinity
- 10 subregions have a high risk or hazard of dryland salinity over more than 10% of their area.
- 9 subregions have more than 10% of their remaining native vegetation coinciding with areas of high risk or hazard of dryland salinity.
Dryland salinity trend assessments undertaken as part of the Audit predict that by the year 2050.
- areas of high risk or hazard of dryland salinity will exceed 10% in 32 subregions.
- The area of high risk or hazard of dryland salinity will coincide and threaten more than 10% of the remaining native vegetation in 22 subregions.
Threatened species
High numbers of nationally listed threatened plants and animals are concentrated in some subregions. More detailed analysis at the species level is required to explain this concentration.
- 38 subregions, mainly in the intensive use zone, are known to contain more than 30 threatened plant species.
- 96 subregions, again mainly in the intensive use zone, have more than 10 threatened vertebrate animal species.
Landscape stress
Continental landscape stress rates subregions over six stress classes.
Representatives of the two highest stress classes have little natural vegetation remaining and that which does remain is under increasing stress from a variety of threatening processes. Landscape scale responses are required in these subregions to prevent further decline and to maximise the protection of remaining subregional biodiversity. Highest priority should be given to protecting and managing the remaining native vegetation coupled with revegetation strategies that concentrate on restoring or enhancing connectivity and increasing the area of more significant remnants.
- 37 subregions (10%) fall into the two highest stress classes; they are all in the intensive use zone.
These endangered subregions are mainly concentrated in the south-east of the continent and include south-eastern South Australia, much of Victoria and the South Eastern Highlands, and the Upper Slopes and Lower Slopes subregions of southern New South Wales. Outside this area other endangered subregions include the Avon Wheatbelt and Dandarragan Plateau in south-west Western Australia, the Northern Midlands subregion in Tasmania and a number of subregions in Queensland within the Wet Tropics (lowlands), Mulga lands, South East Queensland and Brigalow Belt (North and South) bioregions. Two Southern Brigalow Belt subregions in northern New South Wales also fall within the endangered category.
Subregions within the two lowest stress classes are considered to be in relatively good health.
- 152 subregions fall into the two lowest stress classes.
These lower stress class subregions are the subregions of marginal value to agriculture or pastoralism. They are distributed equally across the intensive use zone and the extensive use zone. Relative to other subregions, weeds and feral animals are not yet as great a threat to biodiversity and landscape health. These regions provide opportunities for cost-effective and sustainable biodiversity conservation strategies to be implemented. Clearing is continuing in some of these subregions.
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