The Esperance mallee is an ecoregion in southwestern Australia amounting to approximately 44,600 squares miles in terrestrial extent. It is classified within the Mediterranean Forests, Woodlands and Shrub biome. About one half of the land area of this ecoregion is currently being used for agriculture, with most of the damage from agricultural clearance having been carried out in government sponsored public works programs.
There are a total of 382 recorded macro-fauna in the Esperance Mallee, including numerous special status birds and reptiles. The semi-arid ecoregion boasts a plethora of snakes, including two endemic squamata; there is also one endemic amphibian species, Neobatrachus albipes, in the Esperance Mallee.
Location and General Description
Esperance mallee is an aggregation of the Esperance Plains and Mallee regions of the foundational Iinterim Bogeographic Regionalisation for Australia (IBRA) study. The ecoregion lies just east of the southern portion of the Darlington Range, at the southwest edge of the Great Victoria Desert and is bounded at the south by the Indian Ocean. The southern coastal portion of the ecoregion is known as the Esperance Plains.
The Esperance Plains, sometimes termed the as Eyre Botanical District, is a distinct biogeographic region in southwestern Australia. Situated along the south coast of Australia on the Indian Ocean between the Avon Wheatbelt and Hampton regions, it stretches between Albany and Point Culver on Australia's south coast; moreover, bordered to the north by the Mallee biogeographic region, it is a plain with accents of granitic and quartz outcrops and ranges, with a semi-arid Mediterranean climate and vegetation consisting chiefly of mallee-heath and proteaceous scrub.
The Esperance Plains boasts over 3500 native vascular plant species, and around 300 established naturalized alien species. On the Esperance Plains there have been 72 distinct taxa of endangered plants, with another 433 species having been designated Priority Flora under the Department of Environment and Conservation's Declared Rare and Priority Flora List.
Mallee biogeographic region
Mallee, also called the Roe Botanical District, is a biogeographic region in southern Western Australia. Wedged between the Esperance Plains, Avon Wheatbelt and Coolgardie regions, it manifests a low, gently undulating topography, a semi-arid Mediterranean climate, and extensive Eucalyptus mallee vegetation. About one half of the region has been cleared for intensive agriculture. Recognised as a region under the Interim Biogeographic Regionalisation for Australia (IBRA), predominant soil is sand over clay, overlying Archean and Proterozoic granite of the Yilgarn Craton. At the eastern limits there is some calcareous soil overlying Eocene limestone. The region manifests a low-lying, gently undulating topography, with rather occluded drainage, such that a series of playa lakes is produced.
The Mallee biogeographic region vegetation is predominantly Eucalyptus mallee over an understory of myrtaceous and proteaceous heath. Over half of the land area is vegetated solely by mallee, with a further one fourth chiefly mallee with woodland patches; the latter vegetation occurs mainly on the calcareous soils to the east. The mallee region consists of a number of Eucalyptus species, the most consistent being tall sand mallee (E. eremophila). Seasonally wet and alluvial zones are vegetated by Melaleuca shrublands where freshwater, and Tecticornia low shrublands for saline soils. There are also sporadic thickets of Allocasuarina, particularly on greenstone hills.
Mallee biogeographic region species richness varies between 17 to 48 species per one thousand square metres, depending upon soil nutrients, microclimate and water availability. The lowest species richness occurs in severe habitats such as alongside hypersaline lakes or other saline ponds, as well as within zones of high soil nutrients, where dominant flora suppress competing species. Conversely, the highest species richness occurs in soils with the low soil nutritient content. Most species in the Mallee biogeographic region are killed off by fire, and require regeneration from seed.
Within the Mallee region, there are 3443 native vascular plant species, and a further 239 naturalized alien species. As with other regions in semi-arid areas of the South West, it exhibits high endemism, especially with respect to Eucalyptus and Acacia species. The endangered flora of the Mallee region consists of 55 species, with another 325 species having been designated Priority Flora under Australia's Department of Environment and Conservation's Declared Rare and Priority Flora List
Mallee is a general term to depict a series of eucalypts which exhibit a subsoil bulb structure called a lignotuber, which is attached to the plant's roots. New bulds are able to sprout from the lignotuber subsequent to a wildfire. Mallee trees and accompanying understory shrubs are therefore adapted to the poor soils, lack of rainfall and regular fire disturbance regime of this arid coastal zone.
Tne faunal assemblage of thes ecoregion the coast includes the reptiles: the endemic McKenzie's dragon (Ctenophorus mckenziei), near threatened Bardick snake (Echiopsis curta), the vulnerable endemic E. atriceps, the endemic lerista viduata, and the highly venomous Common Death Adder (Acanthophis antarcticus), An endemic amphibian of the ecoregion is the Neobetrachus albipes; the near threatened Main's ground froglet (Geocrinia lutea) is a special status amphibian of the ecoregion. Mammals within the ecoregion include the near threatened brush-tailed phascogale (Phascogale tapoatafa), near threatened red-tailed wambenger (P. calura), near threatened western quoll (Dasyurus geoffroii), and the minute honey possum (Tarsipes rostratus) which feeds on nectar of the Australian kangaroo paw flower (Anigozanthos manglesii).
Birds include the endangered western whipbird, endangered Australasian bittern (Botaurus poiciloptilus), endangered slender-billed black cockatoo (Calyptorhynchus latirostris), endangered white-tailed black cockatoo (C. baudinii), vulnerable fairy tern (Sterna nereis), vulnerable great knot (Puffinus tenuirostris), vulnerable far eastern curlew (Numenius madagascariensis), vulnerable malleefowl (Leipoa ocellata), near threatened black-tailed godwit (Limosa limosa), near threatened blue-billed duck (Oxyura australis), near threatened buff-breasted sandpiper (Tryngites subruficollis), near threatened letter-winged kite (Elanus scriptus), western ground parrot, red-winged fairywren (Malurus elegans), Australian white ibis (Threskiornis moluccus) and the rare Cape Barren goose (Cereopsis novaehollandiae) in the coastal zone..
The principal vegetative assemblage of the Esperance Plains region is mallee-heath; which covers around 58 percent of the plains. Other key flora forms include mallee (17 percent), scrub-heath (13 percent) and coastal dune scrub (4 percent). Only a very small amount of woodland is found on the plains; the only woodland communities being dominated by Eucalyptus marginata (Jarrah), Corymbia calophylla (Marri) and E. wandoo (Wandoo) in valleys of the Stirling Mountains (one percent); and limited amounts of E. loxophleba (York Gum) and Eucalyptus occidentalis (Flat-topped Yate) woodland in certain low-lying areas. There is also a rather small amount of low forest on the coastal islands out in the Indian Ocean.
The Esperance Mallee is classified as an ecoregion that is Critical/Endangered. Furthermore the ecoregion is designated as a G200 unit, indication it is of the highest priority for ecoregion protection
Type and severity of threats
A considerable fraction of the land area spanned by this ecoregion is presently being utilised for agriculture, such that the natural environment is under ongoing threat from clearance, leading to habitat fragmentation and over-irrigation; moreover, wildlife is vulnerable ton introduced alien species such as foxes.
Justification of ecoregion delineation
Justification for ecoregion delineation: The Esperance Mallee ecoregion includes two IBRAs, the Mallee and the Esperance Plains biogeographic regions (Thackway and Cresswell 1995). The Esperance Mallee ecoregion is part of the Southwest Botanical Province Centre of Plant Diversity, and includes both the Roe and Eyre Districts (Beard 1995). The Esperance Mallee also represents the eastern extension of the Southwest Australia Endemic Bird Area (Stattersfield et al. 1998). Vegetation is predominantly shrublands and open shrublands of mallee, with a semi-arid Mediterranean climate.
- Beard, J. S. 1995. South-west 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.
- Shepherd, D. P., G. R. Beeston and A. J. M. Hopkins. Native vegetation in Western Australia: Extent, Type and Status. Resource Management Technical Report No. 249. Department of Agriculture and Food, Government of Western Australia
- Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wedge. 1998. Endemic Bird Areas of the World. Priorities for biodiversity conservation. BirdLife Conservation Series No. 7. BirdLife International, Cambridge, United Kingdom.
- Thackway, R and I D Cresswell (1995) An interim biogeographic regionalisation for Australia : a framework for setting priorities in the National Reserves System Cooperative Program Version 4.0 Canberra : Australian Nature Conservation Agency, Reserve Systems Unit, 1995.
- World Wildlife Fund. 2009. Esperance Mallee
Some of the text for the Ecoregion Delineation section was prepared by Angas Hopkins of the World Wildlife Fund