Southwest Australia is a

biogeographic region An ecoregion (ecological region) or ecozone (ecological zone) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than a biogeographic realm. Ecoregions cover relatively large areas of l ...

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to t ...

. 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, as well as

Kwongan Kwongan is plant community found in south-western Western Australia. The name is a Bibbelmun (Noongar) Aboriginal term of wide geographical use defined by Beard (1976) as Kwongan has replaced other terms applied by European botanists such as ...

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) or ecozone (ecological zone) is an ecologically and geographically defined area that is smaller than a bioregion, which in turn is smaller than a biogeographic realm. Ecoregions cover relatively large areas of ...

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 ( phaneritic) 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 cools and solidifies un ...

gneiss Gneiss ( ) 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. Gneiss forms at higher temperatures a ...

and

laterite Laterite is both a soil and a rock 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 ...

Bluff Knoll Bluff Knoll is the highest peak of the Stirling Range in the Great Southern region of Western Australia (WA). It is above sea level, with a prominence of 650 m (2,130 ft). The local Aboriginal people, the Mineng and Koreng/Goreng s ...

in the

Stirling Range The Stirling Range or Koikyennuruff is a range of mountains and hills in the Great Southern region of Western Australia, south-east of Perth. It is over wide from west to east, stretching from the highway between Mount Barker and Cranb ...

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 temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...

, 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 characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Dep ...

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 In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

. 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 recognized as a floristic province. Vegetation in the region is mainly woody, including

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

woodland A woodland () is, in the broad sense, land covered with trees, 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 sunlight and limited shade (see ...

shrubland Shrubland, scrubland, scrub, brush, or bush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes. Shrubland may either occur naturally or be the result of human activity. It ...

s, and

heathland A heath () is a shrubland habitat found mainly on free-draining infertile, acidic soils and 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 dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...

s. Predominant vegetation types are ''

Eucalyptus ''Eucalyptus'' () is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with several other genera in the tribe Eucalypteae, including '' Corymbia'', they are commonly known as ...

'' woodlands, eucalyptus-dominated mallee shrublands, and

kwongan Kwongan is plant community found in south-western Western Australia. The name is a Bibbelmun (Noongar) Aboriginal term of wide geographical use defined by Beard (1976) as Kwongan has replaced other terms applied by European botanists such as ...

shrublands and heathlands, which correspond to the

chaparral Chaparral ( ) is a shrubland plant community and geographical feature found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterranea ...

matorral 300px, Springtime in Chilean matorral a few kilometers north of Santiago along the Pan-American Highway Matorral is a Spanish language, Spanish word, along with ''tomillares'', for shrubland, thicket or bushes. It is used in naming and describin ...

maquis Maquis may refer to: Resistance groups * Maquis (World War II), predominantly rural guerrilla bands of the French Resistance * Spanish Maquis, guerrillas who fought against Francoist Spain in the aftermath of the Spanish Civil War * The netwo ...

, and

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

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 withi ...

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

endemic Endemism is the state of a species being found 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 found else ...

species, notably among the protea family (

Proteaceae The Proteaceae form a family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genera with about 1,660 known species. Together with the Platanaceae and Nelumbonaceae, they make up the order ...

). Southwest Australia is home to many endemic carnivorous plants, including more than half the world's species of sundews (''Drosera''), the bladderwort subgenus '' Polypompholyx'', the ''Byblis gigantea'' complex of rainbow plants (composed of two species, '' Byblis lamellata'' and '' B. gigantea''), and the pitcher plant '' Cephalotus follicularis'', sole species in the plant family Cephalotaceae.

Fauna

The

honey possum The honey possum or noolbenger (''Tarsipes rostratus''), is a tiny species of marsupial that feeds on the nectar and pollen of a diverse range of flowering plants. Found in southwest Australia, it is an important pollinator for such plants as '' ...

(''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 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 the m ...

for several southwestern plants including ''

Banksia attenuata ''Banksia attenuata'', commonly known as the candlestick banksia, slender banksia, or biara to the Noongar people, is a species of plant in the family Proteaceae. Commonly a tree, it reaches high, but it is often a shrub in drier areas high. I ...

, 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 descr ...

''. 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 An Endemic Bird Area (EBA) is an area of land identified by BirdLife International as being important for habitat-based bird conservation because it contains the habitats of restricted-range bird species (''see below for definition''), which are th ...

, 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'' found in southwest Australia. The epithet commemorates the French explorer Nicolas Baudin. It has a ...

(''Zanda baudinii''),

western corella The western corella (''Cacatua pastinator'') also known as the western long-billed corella, is a species of white cockatoo endemic to south-western Australia. Taxonomy Cacatuidae is one of three families of the large and diverse avian order Psi ...

(''Cacatua pastinator''),

noisy scrubbird The noisy scrubbird (''Atrichornis clamosus'') is a species of bird in the family Atrichornithidae. It is endemic to the coastal heaths of south-western Australia (east of Albany). Description The noisy scrubbird features a dark brown colou ...

(''Atrichornis clamosus''), red-winged fairywren (''Malurus elegans''), western bristlebird (''Dasyornis longirostris''), black-throated whipbird (''Psophodes nigrogularis''),

white-breasted robin The white-breasted robin (''Eopsaltria georgiana'') is a passerine bird in the Australasian robin family Petroicidae and the Yellow Robin genus Eopsaltria. Occasionally it is placed in the genus ''Quoyornis''. It is endemic to southwestern Austra ...

(''Eopsaltria georgianus''), and

red-eared firetail The red-eared firetail (''Stagonopleura oculata''), also known as the boorin, is a small finch-like species of bird. It occurs in dense wetland vegetation of coastal to sub-coastal regions in Southwest Australia. Its appearance is considered app ...

(''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 Inc. (WWF) is an 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 the W ...

and Interim Biogeographic Regionalisation for Australia (IBRA) divide the region into six ecoregions and ten biogeographic regions: * Coolgardie woodlands (IBRA Coolgardie and Hampton) * Esperance mallee (IBRA

Esperance Plains Esperance Plains, also known as Eyre Botanical District, is a biogeographic region in southern Western Australia on the south coast between the Avon Wheatbelt and Hampton bioregions, and bordered to the north by the Mallee region. It is a ...

and Mallee) * Jarrah-Karri forest and shrublands (IBRA Warren) * Southwest Australia savanna (IBRA Geraldton Sandplains, Avon Wheatbelt, and Yalgoo) * Southwest Australia woodlands (IBRA

Jarrah Forest Jarrah forest is tall open forest in which the dominant overstory tree is ''Eucalyptus marginata'' (jarrah). The ecosystem occurs only in the Southwest Botanical Province of Western Australia. It is most common in the biogeographic region named in ...

) * Swan Coastal Plain scrub and woodlands (IBRA Swan Coastal Plain) 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 The Eremaean province is a botanical region in Western Australia, characterised by a desert climate. It is sometimes referred to as the ''dry and arid inland'' or ''interior'' region of Western Australia It is one of John Stanley Beard's phytoge ...

by the Western Australian Herbarium.

Freshwater

Southwest Australia has several permanent rivers and streams, including the

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

– Avon system, the

Blackwood River The Blackwood River is a major river and catchment in the South West of Western Australia. Course The river begins at the junction of Arthur River and Balgarup River near Quelarup and travels in a south westerly direction through the tow ...

, and other short rivers. The perennial rivers drain from the interior plateau and

Darling Range The Darling Scarp, also referred to as the Darling Range or Darling Ranges, is a low escarpment running north–south to the east of the Swan Coastal Plain and Perth, Western Australia. The escarpment extends generally north of Bindoon, to th ...

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 The Arrowsmith River lies within the Mid West region of Western Australia. The explorer George Grey found the river on 11 April 1839, on his second expedition along the west coast. He named it after the distinguished English cartographer J ...

north of

Perth Perth is the capital and largest city of the Australian state of Western Australia. It is the fourth most populous city in Australia and Oceania, with a population of 2.1 million (80% of the state) living in Greater Perth in 2020. Perth is ...

, 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 An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...

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 Aestivation ( la, aestas (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a ...

during the summer months, an adaptation to the region's dry summers. Other endemic species are the

nightfish The nightfish (''Bostockia porosa'') is a species of freshwater ray-finned fish, a temperate perch from the family Percichthyidae which is endemic to southwestern Australia. Taxonomy The nightfish was first formally described in 1873 by ...

(''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 Devil's Lair is a single-chamber cave with a floor area of around that formed in a Quaternary dune limestone of the Leeuwin–Naturaliste Ridge, from the modern coastline of Western Australia. The stratigraphic sequence in the cave floor ...

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 settlment 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 peoples who live in the South West, Western Australia, south-west corner of Western Australia, from Geraldton, Western Au ...

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 Vegetation of Australia