Southwest Australia

Southwest Australia is a biogeographic region in Western Australia. It includes the Mediterranean-climate area of southwestern Australia, which is home to a diverse and distinctive flora and fauna.

Ecoregions of Southwest Australia, as defined by the WWF. 1. Jarrah-Karri forest and shrublands; 2. Southwest Australia woodlands; 3. Southwest Australia savanna; 4. Coolgardie woodlands; 5. Esperance mallee.

The region is also known as the Southwest Australia Global Diversity Hotspot,[1][2][3] as well as Kwongan.[4]

Geography

The region includes the Mediterranean forests, woodlands, and scrub ecoregions of Western Australia. The region has a wet-winter, dry-summer Mediterranean climate, one of five such regions in the world. 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, gneiss and laterite. 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.

Flora
See also: Flora of Western Australia

Vegetation in the region is mainly woody, including forests, woodlands, shrublands, and heathlands, but no grasslands. Predominant vegetation types are Eucalyptus 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 species, notably among the protea family (Proteaceae).

Southwest Australia is recognized as a floristic province.[5]

Ecoregions

The World Wide Fund for Nature and Interim Biogeographic Regionalisation for Australia (IBRA) divide the region up into a number of ecoregions:

The transitional Coolgardie, Hampton, and Yalgoo regions 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.[6]

Freshwater
See also: South West drainage division

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, most often in areas with 700 mm or more of annual rainfall.[7]

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.[7]

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 adapation 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),[7] 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.[7]

The southwestern snake-necked turtle (Chelodina colliei) and western swamp turtle (Pseudemydura umbrina) are aquatic species endemic to Southwest Australia.

Conservation

The context of the region in European colonist histories of the region is of limited understanding knowledge of the country[8] as opposed to the indigenous understanding.[9]

See also

References
  1. Wardell-Johnson, Grant; Wardell-Johnson, Angela; Bradby, K; Robinson, Todd; Bateman, Bill; Williams, K; Braun, K; Beckerling, J; Burbridge, Michael (2016), Application of a Gondwanan perspective to restore ecological integrity in the south-western Australian global biodiversity hotspot, Department of Environment and Agriculture, retrieved 11 October 2016
  2. Burbidge, Andrew (1 February 2010), "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.(Focus)", Ecos, CSIRO Publishing (153): 18(2), ISSN 0311-4546
  3. Lambers, H., (editor.) (2014), Plant life on the sandplains in southwest Australia : a global biodiversity hotspot : kwongan matters, Crawley, Western Australia UWA Publishing, ISBN 978-1-74258-564-2CS1 maint: multiple names: authors list (link) CS1 maint: extra text: authors list (link)
  4. http://www.wildlifetourism.org.au/southwest-australian-biodiversity-hotspot-tourist-destination/
  5. Cook, Lyn G; Hardy, Nate B; Crisp, Michael D (1 July 2015), "Three explanations for biodiversity hotspots: small range size, geographical overlap and time for species accumulation. An Australian case study", New Phytologist, Wiley Subscription Services, Inc, 207 (2): 390(11), doi:10.1111/nph.13199, ISSN 0028-646X
  6. "FloraBase - the Western Australian Flora". Department of Environment and Conservation. Retrieved 25 October 2011.
  7. Unmack, Peter. "Southwestern Australia". Freshwater Ecoregions of the World. Accessed 17 June 2020.
  8. Bunbury, Bill (2015), Invisible country : South-west Australia: understanding a landscape, Crawley, Western Australia UWA Publishing, ISBN 978-1-74258-625-0
  9. Cunningham, Irene; Saunders, Denis; Cunningham, Irene (2005), The land of flowers : an Australian environment on the brink, Otford Press, ISBN 978-1-876928-45-2

Further reading

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