CEPF
Protecting Nature's Hotspots for people and prosperity

Southwest Australia

Tab 1

Overview

The forest, woodlands, shrublands, and heath of Southwest Australia are characterized by high endemism among plants and reptiles. Its unique vertebrate species include the numbat, honey possum, and the red-capped parrot. The western swamp turtle, which hibernates for nearly eight months of the year in response to dry conditions and hot temperatures, may be the most threatened freshwater turtle species in the world, although a successful conservation program has allowed its numbers to increase.

The primary cause of habitat loss in Southwest Australia has been agricultural expansion, which is accentuated by extensive fertilizer use. A major threat for the native fauna has been the introduction of ivasive alien species like foxes and cats.

VITAL SIGNS

Hotspot Original Extent (km²) 356,717
Hotspot Vegetation Remaining (km²) 107,015
Endemic Plant Species 2,948
Endemic Threatened Birds 3
Endemic Threatened Mammals 6
Endemic Threatened Amphibians 3
Extinct Species† 2
Human Population Density (people/km²) 5
Area Protected (km²) 38,379
Area Protected (km²) in Categories I-IV* 38,258
†Recorded extinctions since 1500. *Categories I-IV afford higher levels of protection.

OVERVIEW

The Southwest Australia Hotspot occupies some 356,717 km² on the southwestern tip of Australia, in the state of Western Australia. As defined, this hotspot comprises the Southwest Botanical Province, but excludes the neighboring Southwestern Interzone. As this hotspot is one of five Mediterranean-type ecosystems in the world, most rain falls during the winter months and the summers are characteristically dry. A broad coastal plain 20-120 kilometers wide grades into gently undulating uplands, with weathered granite, gneiss and lateritic formations. Further inland, rainfall decreases and the length of the dry season increases.

Native plants are well adapted to the nutrient-poor sandy and lateritic soils, which also support broadacre cropping and sheep grazing. Vegetation in the province is mainly woody, comprising forests, woodlands, shrublands, and heaths, but no grasslands. Principal vegetation types in this region are Eucalyptus woodlands, and the Eucalyptus-dominated "mallee" shrubland. Kwongan is a term adapted from the Aboriginal Noongar language to cover the various Western Australian types of shrubland, comparable with the maquis, chaparral, and fynbos of other countries with Mediterranean-type systems. The principal structural types of Kwongan are thicket, scrub-heath, and heath, which together comprise about 30 percent of the original vegetation. A number of vegetation units are endemic, including some types of eucalyptus forests and some forms of kwongan.

Tab 2

Species

Unique biodiversity

DIVERSITY & ENDEMISM

Taxonomic Group Species Endemic Species Percent Endemism
Plants 5,571 2,948 52.9
Mammals 59 12 20.3
Birds 285 10 3.5
Reptiles 177 27 15.3
Amphibians 32 22 68.8
Freshwater Fishes 20 10 50.0

Impressive plant endemism in Southwest Australia is attributed to millions of years of isolation from the rest of Australia by the country's vast central deserts. Extreme climate shifts and poor soils also promoted specialization of the region's flora.

PLANTS

Of more than 5,570 species of vascular plants found here, nearly 2,950 are endemic (about 53 percent). A significant number of genera are also endemic: 87 of 697 genera (12.5 percent) are found nowhere else in the world. Additionally, four families are endemic: Ecdeiocoleaceae, Emblingiaceae, Eremosynaceae and the monotypic Cephalotaceae, which is represented by the pitcher plant (Cephalotus follicularis, VU), a carnivorous plant that traps insects in its modified leaves.

The ten largest families in the hotspot (including the Myrtaceae with 785 species, of which 92 percent are endemic, and Proteaceae with 684 species, 96 percent endemic) comprise 61 percent of the flora. The number of species per genus averages eight, although the ten largest genera (including Acacia with 397 species, 51 percent endemic, and Eucalyptus with 246 species, 52 percent endemic) far exceed this figure.

The Banksia plants of the family Proteaceae are among the most distinctive found in this hotspot. These brilliant flowering plants range from trees to small prostrate plants, one of which even has underground stems. Kangaroo paws (Anigozanthos spp.) are another brightly colored flower from the region; their long stems are thought to resemble their namesakes.

The region's flagship tree species include three eucalyptus: jarrah (Eucalyptus marginata), marri (E. calophylla), and karri (E. diversicolor). While jarrah and marri grow to only about 20-30 meters in height, some karri forests have canopies up to 70 meters high, and individual trees may grow as high as 80 meters, ranking this endemic species as one of the tallest trees on earth.

VERTEBRATES

Birds
Over 280 native bird species occur in the region, 12 of which are endemic. The level of endemism is slightly higher than in other Mediterranean-type hotspots, and the region is considered an Endemic Bird Area (EBA) by BirdLife International.

The region is home to 22 parrot species (three endemics), including Carnaby's black-cockatoo (Calyptorhynchus latirostris, EN). The noisy scrub-bird (Atrichornis clamosus, VU), which earned its name because of the loud vocalizations of its males, was presumed extinct until a small population was rediscovered in 1961. Several other bird species are near threatened or rapidly declining in the face of habitat loss, modification and fragmentation or inappropriate fire regimes.

Mammals
This hotspot has roughly 60 native mammal species occurring, of which 12 are endemic, including the mouse-sized, nectarivorous honey possum (Tarsipes rostratus), the only representative of the family Tarsipedidae, which lives only in the coastal plain heaths of Southwest Australia. Another interesting endemic is the quokka (Setonix brachyurus, VU), a small, furry wallaby confined to the mainland, where it has been declining in numbers, and two small offshore islands (Rottnest Island and Bald Island).

Some mammal species have become de facto endemics to Southwest Australia because they are extinct in the rest of their natural ranges. The numbat (Myrmecobius fasciatus, VU), for example, a squirrel-sized marsupial anteater, is the only member of the family Myrmecobiidae, and has become the mammalian symbol of Western Australia. Besides the numbat, four other threatened mammals are endemic to the hotspot, including the most threatened species in the hotspot, Gilbert’s potoroo (Potorous gilberti, CR), which today occurs only in the Two People's Bay Nature Reserve.

Reptiles
As might be expected in a country that leads the world in reptile diversity, there are a wide variety of reptile species in Southwest Australia. Nearly 30 of more than 175 species (15 percent) are endemic to the hotspot. The endemic western swamp turtle (Pseudemydura umbrina, CR), a monotypic genus, is the most threatened reptile in Australia and is among the 25 most threatened freshwater turtle in the world. The wild population of less than 100 is now only found in one or two swamps near Perth.

Other threatened reptiles include the Yinnietharra rock dragon (Ctenophorus yinnietharra, VU), an understudied lizard species that is apparently specialized to two granitic rock outcrops in the region and does not inhabit outcrops of different origins, and the Lake Cronin snake (Echiopsis atriceps, VU) whose very limited range includes unprotected private lands.

Amphibians
There are more than 30 species of amphibian found in this hotspot, nearly two-thirds of which are endemic, including four species that represent endemic genera: the turtle frog (Myobatrachus gouldii), Nicholl's toadlet (Metacrinia nichollsi), Sandhill frog (Arenophryne rotunda), and the harlequin frog (Spicospina flammocaerulea, VU). Besides the last-mentioned species, which was only described in 1997 and is known to have a limited area of occurrence, two other frog species are considered threatened, one of which, the yellow-bellied frog (Geocrinia vitellina, VU), is represented by six populations confined to a 6.3 km² area east of the Leeuwin-Naturaliste Ridge.

Freshwater Fishes
The Southwest Australia hotspot has very little freshwater habitat and thus only about 20 native species of freshwater fish. However, about half of these species and three genera are endemic, the most remarkable being the salamanderfish (Lepidogalaxias salamandroides), which is the only member of the hotspot's single endemic family (Lepidogalaxiidae).

Tab 3

Threats
​Human impacts

The greatest human impact in Southwest Australia has been the clearing of native vegetation for agriculture. Agricultural development began in 1829, with the arrival of the first European settlers to the region. However, because of the poor soils, development progressed slowly until the 1890s, when phosphate fertilizers were introduced. Today, most usable private land in the region is farmed, although it requires the application of phosphate, as well as zinc, copper, cobalt, and molybdenum. Because of the region's long dry seasons, bush fires have traditionally been used for hunting and clearing land. Although native plants are highly adapted to fire, the alteration or intensification of burning regimes can dramatically change the composition and condition of the natural vegetation.

One of the most serious current threats to the natural vegetation of Southwest Australia is the spread of root disease, or "jarrah dieback" caused by the root fungus Phytophthora cinnamomi. The disease was first noticed in the jarrah forests in 1940 but not identified until 1965. By that time, thousands of hectares of forest had been infected and killed. Root disease is now spreading to other habitats, including kwongan shrublands, and in particular Stirling Range National Park, where it has caused mortality among susceptible plants like the grass trees (Xanthorrhoea spp.) and members of the Proteaceae, especially the Banksias.

Large-scale mining for bauxite is increasingly a threat to Southwest Australia's ecosystems; the region is one of the largest producers of alumina in the world. Open-pit mining destroys habitats and pollutes waterways. However, recent reclamation efforts have been successful at establishing native plants in abandoned mine pits, a technique that holds promise for land management in the region.

Introduced alien species, especially foxes and cats, threaten native fauna and have caused major declines in species like the numbat in Southwest Australia. Land managers have successfully poisoned these alien species with sodium flouroacetate; amazingly, native mammals are immune to the poison because the compound occurs naturally in the leaves of many native legumes.

Today, of the principal vegetation types found in the region, 89 percent of the Eucalyptus woodlands have been lost, while 50 percent of the Eucalypt-dominated mallee and 59 percent of the Kwongan heath formations have been cleared. In total, only 30 percent of the original vegetation remains in more or less pristine condition.

Tab 4

Projects
​Conservation actions and protected areas

A total of about 38,000 km², 11 percent of the land area in Southwest Australia, is under some form of official protection, virtually all of it in IUCN categories I to IV. Many reserves, however, are too small to adequately protect biological resources, and many ecosystem types are not well represented in the protected area system. Typically, the region's reserves represent land that was unsuitable for farming in the early days of settlement. Arable lands are almost exclusively privately owned, and a number of rare species are found only on these private lands.

Southwest Australia represents one of the best opportunities for long-term conservation among the hotspots because of its relatively low population density. However, immediate action is necessary to ensure the survival of the region's unique and highly threatened flora and fauna. In addition to maintaining the integrity of existing protected areas, the current network should be expanded through the creation of new reserves from private and public lands to represent species and ecosystems not yet protected.

There are a number of conservation programs and projects currently operating in Southwest Australia. The Western Shield Program, run by the Department of Conservation and Land Management, is working to bring at least 13 native fauna species back from the brink of extinction by controlling introduced predators, the fox and feral cat. The main weapon in the fight against these predators is the use of the naturally occurring poison 1080, found in native plants called gastrolobiums or 'poison peas'. While the native animals have evolved with these plants and have a high tolerance to the poison, introduced animals do not.

Project Eden is the arid scientific conservation component of Western Shield. This project uses innovative techniques to eradicate feral herbivores and predators and rejuvenate 105,000 hectares of arid zone habitat on Peron Peninsula at Shark Bay for threatened native fauna, and, to promote their reintroduction into the area.

A project focused on the ecology, abundance and predator dynamics of threatened Shark Bay mammals, has been run by the Sustainable Ecosystems program of CSIRO, the Australian national research agency, in partnership with a local salt mining community at Useless Loop for the past 16 years. This work has studied in detail the life cycle of some of Australia’s most threatened animals on Bernier and Dorre Islands and has reintroduced the western barred bandicoot and burrowing bettong, two species extirpated on the Australian mainland, to Heirisson Prong.

Other conservation projects in Southwest Australia include community-based recovery programs for the threatened Carnaby's black-cockatoo, western ground parrot, dibbler, noisy scrub-bird and malleefowl. These involve organizations such as Birds Australia, WWF, CSIRO, Department of Conservation and Land Management and local Landcare groups.

Tab 5

Sources
​References

Allen, G.R., Midgley, S.H. & Allen, M. 2002. Field Guide to the Freshwater Fishes of Australia. Perth, Australia: Western Australian Museum.

Beard, J.S. 1980. A new phytogeographic map of Western Australia. Res. Notes. W.A. Herbarium 3:37-58.

Beard, J.S. 1990. The Plant Life of Western Australia. Sydney: Kangaroo Press.

Beard, J.S., Chapman, A.R. & Gioia, P. 2000. Species richness and endemism in the western Australian flora. Journal of Biogeography 27: 1257-1268.

Beeston, G., Mlodowski, G., Sanders, A. & True, D. 1996. Remnant Vegetation Inventory in the Southern Agriculture Areas of Western Australia. Department of Agriculture Western Australia, Resource Management Report No. 149.

Bell, D.T., Hopkins, A.J.M. & Pate, J.S. 1984. Fire in the Kwongan. In J.S. Pate & J.S. Beard. (Eds.), Kwongan: The Plant Life of the Sandplain. Nedlands: University of Western Australia Press.

Burbidge, N.T. 1960. The phytogeography of the Australian region. Aust. J. Bot. 8: 75-211.

Pate, J.S. & Beard, J.S. 1984. Kwongan, the Plant Life of the Sandplain. Nedlands: University of Western Australia Press.

Shepherd, D.P., Beeston, G.R. & Hopkins, A.J.M. 2002. Native Vegetation in Western Australia: Extent, Type and Status. Resource Management Technical Report 249. Department of Agriculture, Government of Western Australia.

RELATED LINKS

Australian Conservation Foundation
Australia's Heritage Places: Sustainable Tourism
Southwest Australia Woodlands ecoregion - WWF

Tab 6