Southwest Australia is a biogeographic region in

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 th ...

. 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.

Geography

The region includes the Mediterranean forests, woodlands, and scrub

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 under ...

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. 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 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. Depen ...

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 A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both r ...

. 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 (se ...

s, shrublands, 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 e ...

'' woodlands, eucalyptus-dominated mallee shrublands, and kwongan shrublands and heathlands, which correspond to the chaparral, matorral, maquis, and fynbos shrublands found in other Mediterranean-type regions. The region has generally nutrient-poor sandy or lateritic soils, which has encouraged rich speciation 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). Southwest Australia is home to many endemic carnivorous plants, including more than half the world's species of

sundew ''Drosera'', which is commonly known as the sundews, is one of the largest genera of carnivorous plants, with at least 194 species. 2 volumes. These members of the family Droseraceae lure, capture, and digest insects using stalked mucilaginou ...

s (''Drosera''), the bladderwort subgenus '' Polypompholyx'', the ''Byblis gigantea'' complex of rainbow plants (composed of two species, ''

Byblis lamellata ''Byblis lamellata'' is a carnivorous plant in the Byblidaceae family. It is endemic to Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the isl ...

'' and '' B. gigantea''), and the

pitcher plant Pitcher plants are several different carnivorous plants which have modified leaves known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of what are considered to be "true" pitcher p ...

Cephalotus follicularis ''Cephalotus'' ( or ; Greek: ''κεφαλή'' "head", and ''οὔς''/''ὠτός'' "ear", to describe the head of the anthers) is a genus which contains one species, ''Cephalotus follicularis'' the Albany pitcher plant, a small carnivorous pi ...

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

Banksia coccinea ''Banksia coccinea'', commonly known as the scarlet banksia, waratah banksia or Albany banksia, is an erect shrub or small tree in the family (biology), family Proteaceae. Its distribution in the wild is along the Southwest Australia, south wes ...

'', and '' Adenanthos cuneatus''. Other mammals endemic to Southwest Australia are the

western brush wallaby The western brush wallaby (''Notamacropus irma''), also known as the black-gloved wallaby, is a species of wallaby found in the southwestern coastal region of Western Australia. The wallaby's main threat is predation by the introduced red fox (' ...

(''Macropus irma'') and the

quokka The quokka (''Setonix brachyurus'', ) is a small macropod about the size of a domestic cat. It is the only member of the genus ''Setonix''. Like other marsupials in the macropod family (such as kangaroos and wallabies), the quokka is herbivo ...

(''Setonix brachyurus''). Southwest Australia is an Endemic Bird Area, with several

species of birds including the long-billed black cockatoo (''Zanda baudinii''), western corella (''Cacatua pastinator''), noisy scrubbird (''Atrichornis clamosus''),

red-winged fairywren The red-winged fairywren (''Malurus elegans'') is a species of passerine bird in the Australasian wren family, Maluridae. It is non-migratory and endemic to the southwestern corner of Western Australia. Exhibiting a high degree of sexual dimorph ...

(''Malurus elegans''), western bristlebird (''Dasyornis longirostris''),

black-throated whipbird The black-throated whipbird (''Psophodes nigrogularis'') is a passerine bird found in several scattered populations in Southwest Australia. It is predominantly olive green in colour. It was formerly considered to be conspecific with the white-be ...

(''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 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 Wor ...

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

Hampton Hampton may refer to: Places Australia *Hampton bioregion, an IBRA biogeographic region in Western Australia *Hampton, New South Wales *Hampton, Queensland, a town in the Toowoomba Region * Hampton, Victoria Canada * Hampton, New Brunswick *Ha ...

) *

Esperance mallee Esperance mallee is an ecoregion on the south coast of Western Australia, a coastal strip where the predominant vegetation consists of short eucalyptus trees and shrubs. Location and description A part of the Mediterranean forests, woodland ...

(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 p ...

and Mallee) * Jarrah-Karri forest and shrublands (IBRA Warren) * Southwest Australia savanna (IBRA

Geraldton Sandplains Geraldton (Wajarri: ''Jambinu'', Wilunyu: ''Jambinbirri'') is a coastal city in the Mid West region of the Australian state of Western Australia, north of the state capital, Perth. At June 2018, Geraldton had an urban population of 37,648. ...

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 reli ...

, 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 i ...

) *

Swan Coastal Plain scrub and woodlands 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 ...

(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 by the

Western Australian Herbarium The Western Australian Herbarium is the State Herbarium in Perth, Western Australia. It is part of the State government's Department of Parks and Wildlife, and has responsibility for the description and documentation of the flora of Western Austr ...

Freshwater

Southwest Australia has several permanent rivers and streams, including the Swan– Avon system, the Blackwood River, 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 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 i ...

, 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 Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...

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

(''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 The western galaxias (''Galaxias occidentalis''), also called the western minnow, is a species of fish in the genus Galaxias of small, Southern Hemisphere freshwater fish of the family ''Galaxiidae''. It is endemic to southwestern Australia. ...

(''Galaxias occidentalis''). Southwest Australian varieties of the diadromous

common galaxias The common galaxias (''Galaxias maculatus'') or inanga (from the Māori ''īnanga'') is a very widespread Southern Hemisphere fish in the family Galaxiidae. It is a slim, narrow fish with a forked tail and a mottled, spotty pattern, typically ...

(''Galaxias maculatus'') and

spotted galaxias Spotted galaxias (''Galaxias truttaceus'') is a largish, primarily-freshwater galaxias species found in southern Australia. Spotted galaxias are perhaps the most beautiful of the Australian galaxias species. They are a somewhat tubular, deep-bo ...

(''Galaxias truttaceus'') have adapted so they can live their life-cycle and reproduce in fresh water. The

southwestern snake-necked turtle The oblong turtle (''Chelodina oblonga''), also known commonly as the narrow-breasted snake-necked turtle and the southwestern snake-necked turtle, is a species of turtle in the family Chelidae. The species is endemic to the southwestern part o ...

(''Chelodina colliei'') and

western swamp turtle The western swamp turtle or western swamp tortoise (''Pseudemydura umbrina'') is a critically endangered species of freshwater turtle endemic to a small portion of Western Australia. It is the only member of the genus ''Pseudemydura'' in the mon ...

(''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 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 corner of Western Australia, from Geraldton on the west coast to Esperance on the so ...

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