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Case Study

Mitchell (Northern Kimberley 1) Lowest stress class

The Mitchell subregion is the dissected plateau of the Kimberley Basin. Vegetation includes savannah woodland over high sorghum grasses, and hummock grasses on shallow sandy soils on sandstone outcrops. Riparian closed forests of Melaleuca and Pandanus occur along drainage lines. Land uses include grazing on native pastures, Aboriginal use, mining, reserves and conservation.

There are a variety of rare features in the subregion, including:

• a sunken coastline with extensive coastal archipelagos that form a microcosm;
• mound springs and swamp rainforests;
• tropical laterite flora that includes a palmdominated landscape unique in Western Australia;
• and Airfield Swamp on the Mitchell Plateau, a large perched wetland supporting paperbark forest.

There are animals of special interest such as Isoodon auratus (Golden Bandicoot), Wyulda squamicaudata (Scaly-tailed Possum), Petrogale burbidgei (Monjon), Peradorcas concinna (Nabarlek), Mesembriomys macrurus (Golden-backed Tree-rat), Zyzomys woodwardi (Kimberley Rock-rat), Morelia carinata (Rough-scaled Python), Amytornis housei (Black Grasswren). The subregion is fox- and rabbit-free and virtually uninhabited by humans. There are endemic species of possums, birds, reptiles and frogs. There are 12 endemic plants. Rainforest patches are particularly rich in endemic invertebrates, especially Camaenid land snails and earthworms.

Condition and trend

Wetlands and riparian zones within the subregion are in either good or near pristine condition. However, their trend is either unknown or declining. There are three threatened ecological communities and a further 14 ecosystems are considered to be at risk. Most are static or declining, although trends in some are unknown. Very little is known about trends and threatening processes affecting species at risk. Of the six that can be assessed, only the estuarine crocodile is improving; all others are declining. The north-western part of the sub-region is thought to have an intact mammal fauna, including its original component of critical weight range species.

Threatening processes

Parts of the subregion have been subject to a variety of threatening processes. The increasing incidence of late dry season fires is a matter of concern at the landscape scale. Impacts include changes to the savannah's perennial plant/annual grass dynamic, micro-hydrology, erosion processes and river dynamics. Rainforest patches are under threat from fire and stock. Ecosystems are simplifying as grasslands become dominated by annual species. These problems are exacerbated by damage to soils and native grasses caused by stock and feral animals. Overall there is a reduction in productivity and changes to the carrying capacity of the environment for critical weight range mammals and savannah birds. The subregion has a small but growing problem with weeds, and further introductions of exotic plant species are likely. Feral cats are common and other exotic predators pose potential threats, including Bufo marinatus and Rattus exulans.

The arrival of the cane toad is inevitable. Rapid increases in tourist visitation are also affecting parts of the subregion.

Management responses

Management responses have involved planning and recovery actions for both ecosystems and species. Flora has generally been more of a problem than vertebrate fauna in the recovery planning process, because it requires far more extensive surveys to clarify status and to identify habitat associations and potential threatening processes. No recovery plans exist yet for the ecosystems at risk, although research into the status and recovery for some ecosystems is being carried out. Fire, grazing pressure and other threatening processes are being addressed in a limited way, but need significant support and encouragement to maintain and accelerate cultural change. Processes to encourage a perpetual commitment to biodiversity conservation must also be developed.

There are opportunities for joint management arrangements between the State conservation agency and Aboriginal groups. Developing an involvement by the traditional owners in the management of this subregion is seen as a constructive step towards improving biodiversity conservation. In recent years, several pastoral leases have been purchased for tourism (e.g. Drysdale River) and protection of Bradshaw art sites (e.g. Theda, Doongan).

Limiting factors

Twenty vegetation units and 10 ecosystems at risk are not captured by the bioregion's reserve system; more than 66% of the region's vegetation units are not reserved. The three main constraints on reserve acquisition are:

1. Competing land uses, mainly for pastoral production.
2. High land prices for pastoral leases.
3. Insufficient resolution of biodiversity patterns to accurately define all acquisition priorities on the ground.

Management capacity is constrained by resources available and a very low resident human population able to get involved in management activities and, associated with this, the lack of adequately trained personnel. There is also a need to increase awareness of conservation values throughout the community, and encourage a change in attitudes towards the value of conservation.

Future scenarios

Biodiversity conservation needs to be integrated with all land use activities rather than being seen as an imposition.

A quantitative survey and monitoring program for biodiversity, including pastoral lands, is needed to assess condition and provide a benchmark for determining trends. Challenges include the vast and remote nature of the areas involved, building capacity and adequate training, resources to tackle sustainability problems, and that the monitoring must be adopted by all stakeholders rather than being seen as a theoretical exercise undertaken by government. The program would yield a better understanding of sustainability of the various landuse activities at different levels of intensity. There is no code of practice for pastoralism. There has been an unwillingness to apply existing legislation aimed at protecting land condition. Some relevant legislation needs to be revised, and corresponding institutional reforms adopted, including the need for an array of government departments, stakeholders and community groups to co-operate in planning and in initiating specific investigations into the types, mechanism, impacts and amelioration of threatening processes.

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