Southwest Australia is a biogeographic region in

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

. It includes the Mediterranean-climate area of southwestern Australia, which is home to a diverse and distinctive flora and fauna. The region is also known as the Southwest Australia Global Diversity Hotspot.

Geography

The region includes the

Mediterranean forests, woodlands, and scrub Mediterranean forests, woodlands and scrub is a biome defined by the World Wide Fund for Nature. The biome is generally characterized by dry summers and rainy winters, although in some areas rainfall may be uniform. Summers are typically hot in ...

ecoregion An ecoregion (ecological region) is an ecological and geographic area that exists on multiple different levels, defined by type, quality, and quantity of environmental resources. Ecoregions cover relatively large areas of land or water, and c ...

s of Western Australia. The region covers 356,717 km², consisting of a broad coastal plain 20–120 kilometres wide, transitioning to gently undulating uplands made up of weathered

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

gneiss Gneiss (pronounced ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under p ...

and

laterite Laterite is a soil type rich in iron and aluminium and is commonly considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, because of high iron oxide content. They develop by intensive and prolo ...

. Bluff Knoll in the Stirling Range is the highest peak in the region, at 1,099 metres (3,606 ft) elevation. Desert and xeric shrublands lie to the north and east across the centre of Australia, separating Southwest Australia from the other Mediterranean and humid-climate regions of the continent.

Climate

The region has a wet-winter, dry-summer

Mediterranean climate A Mediterranean climate ( ), also called a dry summer climate, described by Köppen and Trewartha as ''Cs'', is a temperate climate type that occurs in the lower mid-latitudes (normally 30 to 44 north and south latitude). Such climates typic ...

, one of five such regions in the world. During the winter months, westerly winds bring cool weather, clouds, and rainfall to Southwest Australia. In the summer months, the lower-latitude anticyclonic belt, with generally dry easterly winds, moves southwards, increasing temperatures and decreasing rainfall.

Tropical cyclone A tropical cyclone is a rapidly rotating storm system with a low-pressure area, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its locat ...

s, off the shore of northern Western Australia during the December-to-March northern wet season, occasionally reach as far south as Perth before moving inland, bringing floods and damaging winds to the west coast and rain to the dry interior."Climate of Western Australia". Britannica.com. Accessed 29 April 2022

/ref> Rainfall generally decreases from south to north, and with distance from the coast. The highest rainfall is typically in the Warren bioregion, Karri Forest Region between Pemberton and Walpole, up to 1,400 mm (55 inches) annually. The region has been experiencing the effects of human induced

climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

. Average annual rainfall has declined as much as 20% since the 1970s, declining by 10–20 millimetres each decade. Summertime maximum temperatures have increased by 0.1º to 0.3º C per decade, and the average number of days per year over 40º C in Perth has doubled over the last century.Kala, Jatin; Robson, Belinda; Fontaine, Joe; Beatty, Stephen; and Wernberg, Thomas (2021).
Drying land and heating seas: why nature in Australia’s southwest is on the climate frontline
. ''The Conversation'', published 28 October 2021 12.55am EDT. Lower rainfall and higher temperatures have reduced stream flow and inflow into drinking water and irrigation catchments since the 1960s. The summer of 2021/22 was the hottest on record.

Flora

Southwest Australia is recognised as a floristic province. Vegetation in the region is mainly woody, including

forest A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...

woodland A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...

shrubland Shrubland, scrubland, scrub, brush, or bush is a plant community characterized by vegetation dominance (ecology), dominated by shrubs, often also including grasses, herbaceous plant, herbs, and geophytes. Shrubland may either occur naturally o ...

s, and

heathland A heath () is a shrubland habitat found mainly on free-draining infertile, acidic soils and is characterised by open, low-growing woody vegetation. Moorland is generally related to high-ground heaths with—especially in Great Britain—a coole ...

s, but no

grassland A grassland is an area where the vegetation is dominance (ecology), dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes such as clover, and other Herbaceo ...

s. Predominant vegetation types are ''

Eucalyptus ''Eucalyptus'' () is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of ''Eucalyptus'' are trees, often Mallee (habit), mallees, and a few are shrubs. Along with several other genera in the tribe Eucalyp ...

'' woodlands, eucalyptus-dominated mallee shrublands, and kwongan shrublands and heathlands, which correspond to the

chaparral Chaparral ( ) is a shrubland plant plant community, community found primarily in California, southern Oregon, and northern Baja California. It is shaped by a Mediterranean climate (mild wet winters and hot dry summers) and infrequent, high-intens ...

matorral 300px, Springtime in Santiago.html" ;"title="Chilean matorral a few kilometers north of Santiago">Chilean matorral a few kilometers north of Santiago along the Pan-American Highway Matorral is a Spanish language, Spanish word, along with ''tomil ...

, maquis, and

fynbos Fynbos (; , ) is a small belt of natural shrubland or heathland vegetation located in the Western Cape and Eastern Cape provinces of South Africa. The area is predominantly coastal and mountainous, with a Mediterranean climate. The fynbos ...

shrublands found in other Mediterranean-type regions. The region has generally nutrient-poor sandy or lateritic soils, which has encouraged rich

speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

of plants adapted to specific ecological niches. The region hosts a great diversity of

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

species, notably among the protea family (

Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...

). Southwest Australia is home to many endemic carnivorous plants, including more than half the world's species of sundews (''Drosera''), the bladderwort subgenus ''

Polypompholyx ''Utricularia'' subg. ''Polypompholyx'' is a subgenus In biology, a subgenus ( subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included i ...

'', the ''Byblis gigantea'' complex of rainbow plants (composed of two species, '' Byblis lamellata'' and '' B. gigantea''), and the

pitcher plant Pitcher plants are carnivorous plants known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of pitcher plant are considered to be "true" pitcher plants and are formed by specialized ...

'' Cephalotus follicularis'', sole species in the plant family Cephalotaceae.

Fauna

The honey possum (''Tarsipes rostratus'') is a tiny marsupial endemic to Southwest Australia that feeds on nectar and pollen, and is an important

pollinator A pollinator is an animal that moves pollen from the male anther of a flower to the female carpel, stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains. Insects are ...

for several southwestern plants including '' Banksia attenuata, Banksia coccinea'', and ''

Adenanthos cuneatus ''Adenanthos cuneatus'', also known as coastal jugflower, flame bush, bridle bush and sweat bush, is a shrub of the family Proteaceae, native to the south coast of Western Australia. The French naturalist Jacques Labillardière originally desc ...

''. Other mammals endemic to Southwest Australia are the western brush wallaby (''Macropus irma'') and the quokka (''Setonix brachyurus''). Southwest Australia is an Endemic Bird Area, with several

species of birds including the

long-billed black cockatoo Baudin's black cockatoo (''Zanda baudinii''), also known as Baudin's cockatoo or the long-billed black cockatoo, is a species of genus ''Zanda (bird), Zanda'' found in southwest Australia. The epithet commemorates the French explorer Nicolas Bau ...

(''Zanda baudinii''), western corella (''Cacatua pastinator''), noisy scrubbird (''Atrichornis clamosus''), red-winged fairywren (''Malurus elegans''), western bristlebird (''Dasyornis longirostris''), black-throated whipbird (''Psophodes nigrogularis''), white-breasted robin (''Eopsaltria georgianus''), and red-eared firetail (''Stagonopleura oculata''). The western rufous bristlebird (''Dasyornis broadbenti litoralis''), an endemic subspecies of rufous bristlebird, is now extinct.

Ecoregions

The

World Wide Fund for Nature The World Wide Fund for Nature (WWF) is a Swiss-based international non-governmental organization founded in 1961 that works in the field of wilderness preservation and the reduction of human impact on the environment. It was formerly named th ...

and

Interim Biogeographic Regionalisation for Australia The Interim Biogeographic Regionalisation for Australia (IBRA) is a biogeography, biogeographic regionalisation of Australia developed by the Australian government's Department of Sustainability, Environment, Water, Population and Communities ( ...

(IBRA) divide the region into six ecoregions and ten biogeographic regions: * Coolgardie woodlands (IBRA Coolgardie and Hampton) * Esperance mallee (IBRA Esperance Plains and Mallee) * Jarrah-Karri forest and shrublands (IBRA Warren) * Southwest Australia savanna (IBRA

Geraldton Sandplains Geraldton Sandplains is an Interim Biogeographic Regionalisation for Australia, interim Australian bioregion of Western Australia. It has an area of . The Geraldton Sandplains is part of the larger Southwest Australia savanna ecoregion, as asses ...

Avon Wheatbelt The Avon Wheatbelt is a bioregion in Western Australia. It has an area of . It is considered part of the larger Southwest Australia savanna ecoregion. Geography The Avon Wheatbelt bioregion is mostly a gently undulating landscape with low rel ...

, and Yalgoo) * Southwest Australia woodlands (IBRA Jarrah Forest) * Swan Coastal Plain scrub and woodlands (IBRA

Swan Coastal Plain The Swan Coastal Plain in Western Australia is the geographic feature which contains the Swan River as it travels west to the Indian Ocean. The coastal plain continues well beyond the boundaries of the Swan River and its tributaries, as a geol ...

) The transitional Coolgardie, Hampton, and Yalgoo bioregions are generally drier than the rest of the Southwest. They considered part of Southwest Australia by the WWF, but are considered part of the Central Australian or Eremaean Region by the

Western Australian Herbarium The Western Australian Herbarium is the state Herbarium, situated in Perth, the capital of Western Australia. It houses a collection of more than 845,000 dried specimens of plants, algae, bryophytes (mosses, liverworts and hornworts), lichens, fu ...

Freshwater

Southwest Australia has several permanent rivers and streams, including the

Swan Swans are birds of the genus ''Cygnus'' within the family Anatidae. The swans' closest relatives include the goose, geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe (biology) ...

– Avon system, the

Blackwood River The Blackwood River is a major river and catchment in the South West (Western Australia), South West of Western Australia. Course The river begins at the junction of Arthur River (Western Australia), Arthur River and Balgarup River near Que ...

, and other short rivers. The perennial rivers drain from the interior plateau and Darling Range across the coastal plain. Their flow is strongly seasonal, corresponding to the Southwest's wet winter–dry summer weather pattern. The perennial streams extend from east of Esperance on the south coast to the Arrowsmith River north of

Perth Perth () is the list of Australian capital cities, capital city of Western Australia. It is the list of cities in Australia by population, fourth-most-populous city in Australia, with a population of over 2.3 million within Greater Perth . The ...

, most often in areas with 700 mm or more of annual rainfall.Unmack, Peter. "Southwestern Australia". ''Freshwater Ecoregions of the World''. Accessed 17 June 2020

/ref> Arid regions separate Southwest Australia's freshwater habitats from Australia's other year-round rivers. As with its terrestrial flora, Southwest Australia's Mediterranean climate and biogeographic isolation has given rise to a distinct freshwater ecoregion with many endemic species. There are fifteen freshwater fish species, including nine exclusively freshwater species, three estuarine species adapted to brackish water, and three diadromous species that spend part of their life-cycle in the sea. The exclusively freshwater species are endemic to Southwest Australia, as are two estuarine species. The salamanderfish (''Lepidogalaxias salamandroides'') is the sole species in the endemic family Lepidogalaxiidae. Salamanderfish can aestivate during the summer months, an adaptation to the region's dry summers. Other endemic species are the nightfish (''Bostockia porosa''), western mud minnow (''Galaxiella munda''), black-stripe minnow (''Galaxiella nigrostriata''), Balston’s pygmy perch (''Nannatherina balstoni''), western pygmy perch (''Nannoperca vittata''), and western galaxias (''Galaxias occidentalis''). Southwest Australian varieties of the diadromous common galaxias (''Galaxias maculatus'') and spotted galaxias (''Galaxias truttaceus'') have adapted so they can live their life-cycle and reproduce in fresh water. The southwestern snake-necked turtle (''Chelodina colliei'') and western swamp turtle (''Pseudemydura umbrina'') are aquatic species endemic to Southwest Australia.

History

The first evidence of human habitation of the region was 50,000 years ago at Devil's Lair by ancestors of today's Aboriginal people."Hassell, Cleve W., and Dodson, John R. (2003). "The fire history of south-west Western Australia prior to European settlement in 1826-1829". in ''Fire in ecosystems of south-west Western Australia:Impacts and management''. Ian Abbott and Neil Burrows, eds. Backhuys Publishers, 2003, pp. 71–85. Aboriginal populations were generally denser on the coastal plain and along the coastal forest edge, and in the interior woodlands and shrublands, particularly near permanent streams and river estuaries. Population was sparse in the forested areas of the south. Offshore islands were likely uninhabited. The Aboriginal inhabitants deliberately set fires to manage the land and vegetation. Evidence from lake and estuarine sediments and firsthand accounts suggest that fire intervals in well-settled areas were frequent – from one to ten years – compared to unoccupied forests and offshore islands, where fire intervals were 30 to 100 or more years. Frequent burning reduced tree cover and encouraged the growth of grasses, herbs, and low shrubs, fostering open woodlands and savannas and limiting areas of dense forest and thicket.

Noongar The Noongar (, also spelt Noongah, Nyungar , Nyoongar, Nyoongah, Nyungah, Nyugah, and Yunga ) are Aboriginal Australian people who live in the South West, Western Australia, south-west corner of Western Australia, from Geraldton, Western Aus ...

peoples inhabited the western and southern portions of the region. The Noongar comprised 14 groups, which spoke distinct but mutually-intelligible languages. The Nyoongar seasonal calendar includes six different seasons in a yearly cycle. These are Birak, Bunuru, Djeran, Makuru, Djilba and Kambarang. Each of the six seasons represents and explains the seasonal changes seen annually. The flowering of many different plants, the hibernation of reptiles and the moulting of swans are all helpful indicators that the seasons are changing. The first permanent European settlement in the region was in 1826 near present-day Albany. European settlers mostly dispossessed the Aboriginal inhabitants, and established extensive agriculture, including wheat, barley, canola, lupins, and oats. They also introduced sheep and cattle to the region. European settlement also changed the fire regime established by the Aboriginal inhabitants of the land.

Protected areas

109,445 km², or 22.13%, of Southwest Australia's land area is in protected areas."Coolgardie woodlands". DOPA Explorer. Accessed 29 April 2022

/ref>"Esperance mallee". DOPA Explorer. Accessed 29 April 2022

/ref>"Jarrah-Karri forest and shrublands". DOPA Explorer. Accessed 29 April 2022

/ref>"Southwest Australia savanna". DOPA Explorer. Accessed 29 April 2022

/ref>"Southwest Australia woodlands". DOPA Explorer. Accessed 29 April 2022

/ref>"Swan Coastal Plain scrub and woodlands". DOPA Explorer. Accessed 29 April 2022

/ref>

References

External links

Biodiversityhotspots.org: Conservation International − Southwest Australia)
{{Western Australia Biogeography of Western Australia Mediterranean forests, woodlands, and scrub in Australia Floristic provinces Mallee Woodlands and Shrublands Regions of Western Australia South West (Western Australia) Freshwater ecoregions Endemic Bird Areas