Global Hotspot under Stress: While the South-West Corner of Western Australia Is Recognised as a Global Biodiversity Hotspot, Its Unique Ecosystems Have Suffered Land Clearing, Introduced Pests and Weeds, a Changed Fire Regime, Loss of Water and Salinisation. Climate Change May Tip the Balance for Some Species, Unless Effective Action Is Taken

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The south-west of Western Australia, a fiat, stable, highly-weathered low plateau dominated by old landscapes with nutrient-deficient soils, is the only designated global biodiversity hotspot in Australia. (1) Of the 34 such areas worldwide, few are in developed countries.

There are more than 7400 named plant taxa and an estimated 6500 species of vascular flora in Australia's south-west, of which more than 50 per cent occur nowhere else. Local species diversity and endemism is also high. For example, in the Fitzgerald River National Park (329 000 ha) there are 1883 plant taxa of which 72 occur only in the park, while Tutanning Nature Reserve (2000 ha) has 850 species.

Approximately 20 per cent of plant species in the south-west are listed as threatened, rare or poorly known; most threatened endemic taxa are woody species. Most plant species show very high levels of genetic diversity and population differentiation due to local persistence through geological time and natural fragmentation as a result of environmental heterogeneity.

Many taxa have very small geographic ranges. About 100 species of vertebrates are endemic, including the honey possum, quokka, red-capped parrot, western swamp tortoise and sunset frog. Some species that have become extinct elsewhere in Australia, such as the numbat, persist in the southwest. Many invertebrates occur nowhere else.

Sixty-three wetlands of national significance are located in the south-west region. In 2007, 82 threatened ecological communities, 351 threatened plant taxa (111 of which are critically endangered) and 69 threatened non-marine animal taxa (16 mammals, 19 birds, 11 reptiles, 3 frogs, 3 fish and 17 invertebrates) were in the south-west.

Near the south coast, many species and some ecosystems are restricted to hilltops. In the Stirling Range National Park, 20 threatened plant taxa, two threatened animal species and one threatened ecological community are found only at high elevations.

There are numerous Gondwanan relictual species in the south-west corner of the south-west, demonstrating the region's role in harbouring organisms having an ancient genetic lineage. Almost all are dependent on mesic conditions. (2) Many species of aquatic invertebrates are restricted to threatened ephemeral freshwater and brackish water ecosystems.

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Because it has a Mediterranean climate, fire is a major component of south-west ecosystems.

The south-west of Western Australia is the source of significant economic wealth, being Australia's largest cereal cropping area and having major mineral deposits including bauxite, gold and manganese. Other land uses include timber harvesting and tourism.

The state's capital, Perth, lies within the south-west region, and urban expansion and tourism are having a negative impact on coastal and near-coastal lands. Clearing for agricultural and urban use has been extensive. In one subregion, 93 per cent of land has been cleared. (3)

Small habitat remnants make conservation management difficult and limit species movement. Less than two per cent of this subregion is in protected areas. Salinisation is a major threat to both agricultural production and biodiversity conservation.

Catchment management, revegetation and new land use practices are increasingly important.

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In some areas it may become uneconomic to continue traditional farming practices, such as cereal cropping, due to reduced winter rainfall and increased costs. Further development of alternative crops, including those based on indigenous biodiversity, is needed. Some marginal land may be abandoned.

Many plants and ecosystems are threatened by the introduced water mould Phytophthora cinnarnomi. Many animals are threatened by introduced predators. Environmental weeds are an increasing threat to ecosystems and species. …