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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Australian Terrestrial Biodiversity Assessment 2002
Paul Sattler and Colin Creighton
National Land and Water Resources Audit, 2002
ISBN 0 642 3713
Case Study
Mitchell Grass Downs (Partial), Barkly Tableland (Partial) and Georgina Limestone (Mitchell Grass Downs 1, 2 & 3) Third highest stress class
Mitchell Grass Downs of Astrebla spp. and the annual Flinders grass, Iseilema spp.
Photo: P.sattler
The bioregion occupies 92,680 km² in the Northern Territory and Queensland. This case study focuses on the Northern Territory portions. This area is characterised by relatively homogeneous plains of cracking clay soils that support Mitchell (Astrebla spp.) grasslands, Coolibah (Eucalyptus microtheca) and Gidgee (Acacia georginae) woodlands and Bluebush (Chenopodium auricomum) swamps, as well as some large intermittent lakes. These communities have high pastoral value and virtually the entire bioregion (97.2%) is contained within pastoral leases and used for grazing cattle on native pastures. Five large pastoral companies hold more than 80% of the region.
There are three small protected areas within the bioregion with a total area of 556km2 (0.6% of the bioregion area) although only Connell's Lagoon Conservation Reserve is managed as an IUCN category I-IV reserve. The two other reserves are exposed to continual or intermittent grazing pressure. These reserves incorporate samples of 6 of the 26 described vegetation types within the bioregion, and do not represent some vegetation types that are largely restricted to the bioregion. The reserve system is also inadequate in the representation of threatened species and significant wetlands.
The conservation values include a series of large but mostly impermanent wetlands of national significance, with some meeting criteria for international significance. These are important for waterbird populations. The region also has five threatened plants and animals, four of which are associated with wetland riparian areas. The bioregion harbours distinctive biota, although there have been possible losses of some species associated with wetlands and tall grasslands, and declines for species, such as the Flock Bronzewing (Phaps histrionica), which has proven relatively intolerant to changes induced by grazing.
Condition and trend
Much of the region's biota has been retained despite extensive pastoral land use. The very sparse historical record suggests regional losses of at least three mammal species and substantial decline for the Flock Bronzewing pigeon. Recent studies of the response of invertebrates, vertebrates and plants to grazing gradients suggest that a suite of species is disadvantaged by grazing and has probably declined substantially. Nonetheless, grazing pressure in the Northern Territory portion of this bioregion is generally less intensive than that in the Queensland portion where paddock sizes are generally smaller, and where areas are subjected to grazing by sheep.
There is a trend for increased pressure on species disadvantaged by grazing, because of increased development in the Northern Territory portion through proliferation of artificial water points, and more subdivision of paddocks.
Threatening processes
Pastoralism is the most pervasive factor affecting the region's biodiversity, especially in chenopod shrublands (bluebush swamps) and mitchell grasslands. Partly accompanying pastoral management, the region's biota may also be affected by altered fire regimes. There is almost no information available on the response of the region's biota to fire, but the widespread aim of fire exclusion would be detrimental to some species.
Several weed species, most notably parkinsonia (Parkinsonia aculeata), rubber bush (Calotropis procera), mesquite (Prosopis spp.) and noogoora burr (Xanthium occidentale) are generally increasing and are of environmental significance. Prickly acacia (Acacia nilotica) is a major environmental and land use problem in the Queensland portion of the bioregion, and has the potential to become a major pest in the Northern Territory portion.
Feral cats occur at high densities, particularly around bores and other water sources. Other exotic animals recorded include: house sparrow, house mouse, red fox, rabbit and are generally more localised or present less serious problems.
Management responses
Many of the conservation values of the bioregion are likely to be retained under responsible pastoral management that aims to sustain high cover of native perennial grasses. Some of the region's principal pastoral enterprises already operate under environmental codes of conduct which include this goal, and it is widely recognised within the area as the desirable and best practice.
Increased reservation would provide a greater level of security to site-specific values, notably significant wetlands and habitat for threatened species and guarantee the maintenance of some diffuse values such as maintaining populations of grazing sensitive species. Although new reserves need not be large, this approach is likely to be problematical because of the high cost of acquiring pastoral land and opposition from landholders.
A complementary approach to achieving these goals is the development of management agreements with pastoral landholders. This would guarantee the maintenance of a network of ungrazed or lightly grazed areas across the bioregion as on-property conservation areas. A system of management agreements based on existing water-remote areas may be achieved at relatively low cost. Costs would increase substantially if an adequate geographic and environmental spread of on-property conservation areas is to be achieved, as well as the protection of some site-specific values. Incentives and a strategic approach to support management by landholders is an essential first step.
Enhanced conservation management will be best achieved in the context of a detailed land use and conservation plan. Studies over the last few years have provided a good foundation for such a regional plan and it is now timely to develop a planning process, involving community participation and the consideration of a range of land use options and incentive packages.
Limiting factors
The major limiting factor to biodiversity conservation in this region is that the environments are the highest quality lands for pastoralism in northern Australia. Removal of lands from pastoral use to conservation reserves will be costly and unlikely to gain local community support.
Conservation efforts may need to be channelled into improved management of pastoral properties and would be extremely cost effective. Here, the major limiting factor is the impact of such changed management upon pastoral profitability. There are few incentives currently available.
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