The Coolgardie woodlands is an ecoregion situated in southwestern Australia, comprising a land area of approximately 53,100 square miles. The Coolgardie woodlands is classified within the Mediterranean Forests, Woodlands, & Shrub biome. The Coolgardie woodlands is the largest reamaining intact Mediterranean climate woodland on Earth, and this ecoregion hxhibits high species richness, in spite of the superficial appearance of a desiccated land. Soil fertility of this ecoregion is generally quite low, so that agriculture has never played a significant role; however, discovery of gold in the year 1892 generated a wave of alluvial mining, whose peak supported hundreds of miners and support personnel.
Due to the extreme geological stability and absence of glaciation since the Carboniferous period, the soils are low in nutrients and often high in salinity; therefore, the region is considered to have to lowest sheep stocking capacity of any ecoregion on Earth for a vegetative covered area. Maximum sheep stocking carrying capacity of one sheep per square mile is a norm.
Many of the ecoregion's soils are saline and calcareous, and plant species here have had to adapt to the poor soils and harsh, hot arid climate to survive. Prominent vegetation includes mallee, certain eucalyptus species and a wide spectrum of plants from the genus Eremophila.
Location and general description
The Coolgardie woodlands are situated in the southern part of Western Australia, with the ecoregion being considered a climatic transition zone between classic Mediterranean coastal features and the extremely hot arid interior of Western Australia. Average rainfall of the Coolgardie is around 8.7 inches per annum. A portion of the woodlands part of this ecoregion were in earlier historical time denoted as the Coolgardie Botanical District, a locus supporting extensive vegetation of the genus Eremophila.
Much of the soil composition of the northern Coolgardie can be classifed as brown calcareous earths; however, the eastern portions manifest more shallow skeletal calcareous loams, and in the south duplex mallee soils dominate.
Much of the Coolgardie woodlands lies within the administrative region of Goldfields-Esperance, one of the nine governmental units of Western Australia. A smaller portion of the extreme western part of the Coolgardie ecoregion lies within the Wheatbelt administrative region of Western Australia.
Eremophila decipiens The ecoregion's low rolling hills pervaded by limestone soils present many woodlands replete with endemic species of eucalyptus, and the sandy plains portions of the Coolgardie are generally covered in scrub vegetation. Western coastal zones manifest abundant protea flowers, while the arid interior supports acacia tree taxa and kwongan heathland.
There are a number of Eremophila plant associations that typify much of the Coolgardie woodlands. For example in some of the southeastern near-coastal reaches of the Coolgardie, Eremophila miniata open shrubland often forms a sparse low canopy, with a denser low understory of Atriplex vesicaria; such a plant association is common on highly saline soil substrate.
In some of the southern portions of the Coolgardie woodlands, particularly near Norseman, there are frequently tall eucalyptus canopy dominated by an understory of relatively dense Eremophila dempsteri or E. interstans. Here rainfall is slightly higher than the ecoregion average, attaining a value of about 11.4 inches per annum, approaching a more Mediterranean climate, although temperatures are still hot, with January record highs recorded at 46 degrees Celsius. Also in the southern portion of the Coolgardie woodlands, one may find Diociria ternata forming a dense heath understory beneathshrub mallee canopy; this association, for example may be found somewhat north of Frasers Station.
A common plant association in the vicinity of the town of Coolgardie is a dense low-lying heath shrub of Eremophila veronica as understory to a low canopy of shrub mallee (Eucalyptus salubris).
Another association is found in the southwestern part of the Coolgardie region where open mats of Eremophila biserrata are seen under melaleuca scrub and open tree mallee; this assemblage is one of the bleakest barren looking plant assemblies of the ecoregion, and is evidenced for example somewhat to the north of Lake Cronin.
Eremophila falcata has a strong occurrence correlation within the Coolgardie ecoregion, often found on brown calcareous loams in open mulga or eucalptus woodland, where it is frequently the dominant shrub.
Eremophila decipiens and the rare and endangered E. virens are both disturbance opportunists that are found in the ecoregion, especially in the Campion area.
Eremophila caperata is a widespread and locally common plant within the ecoregion. It occurs most often on saline soils and depressions, and most frequently in concert with eucalyptus woodland areas.
Special status birds within the ecoregion are: the Near Threatened Australian bustard (Areodotis australis), the Near Threatened black-tailed godwit (Limosa limosa), the Near Threatened buff-breasted sandpiper (Tryngites subruficollis), the Near Threatened grey falcon (Falco hypoleucos), the Vulnerable malleefowl (Leipoa ocellata) and the Near Threatened western whipbird (Psophodes nigrogularis).
Amphibians occurring in the Coolgardie woodlands which have been classified as threatened or endangered are represented by the Vulnerable Australian ground froglet (Geocrinia vitellina).
Special status reptiles found in the ecoregion are: the Near Threatened Bardick snake (Echiopsis curta) and the Endangered woma (Aspidites ramsayi).
Special status mammals of the Coolgardie are represented by the Vulnerable plains mouse (Pseudomys australis) and the Near Threatened western quoll (Dasyurus geoffroii).
Current ecoregion status
The conservation status of the Coolgardie woodlands is classifeid as Vulnerable by the World Wildlife Fund. Moreover, the ecoregion is given a G200 desgination, meaning that it is among the highest priority for worldwide conservation.
Types and severity of threats
There is a paucity of near term threats due to the inhospitable climate, soil infertility, limited water resources and lack of infrastructure in this ecoregion. If demand for gold were to rise, there is the theoretical possiblity of a renewed gold rush to the region, bringing surface disturbance and increased human population, with attendant road building and other development.
Justification of ecoregion delineation
The Coogardie Woodlands ecoregion comprises the Coolgardie IBRA (Interim Biogeographic Regionalisation for Australia per Thackway and Cresswell, 1995), and consist of mallee scrub and woodlands, transitional from the mediterranean to desert climatic zones. This ecoregion is part of the Southwest Botanical Province Centre of Plant Diversity, and corresponds to the Southwestern Interzone region (per Beard,1995).
References and notes
- J.S.Beard. 1995. Southwest Botanical Province. Pages 484–489 in S.D. Davis, V.H. Heywood and A.C. Hamilton, editors. Centres of plant diversity. Volume 2. Asia, Australasia, and the Pacific. WWF/IUCN, IUCN Publications Unit, Cambridge, UK.
- J.R.Chinnock. 2007. Eremophila and allied genera: a monograph of the plant family Myoporaceae. books.google.com 672 pages
- Arthur Howell. 1902. The Western Australian Gold Fields Mines and Minerals 22: 395.
- R.Thackway and I.D.Cresswell, editors. 1995. An interim biogeographic regionalisation for Australia: a framework for establishing the national system of reserves, Version 4.0. Australian Nature Conservation Agency, Canberra.
- Portions of the Justification for ecoregion delineation section were prepared by Angas Hopkins, World Wildlife Fund