Cobar Peneplain - biodiversity
The vegetation of the Cobar Peneplain is regionally distinctive. The bioregion is characterised by an undulating to hilly landscape with shallow, red earth soils where the vegetation is mainly open woodlands of bimble or poplar box (Eucalyptus populnea), red box (Eucalyptus intertexta) and white cypress (Callitris glaucophylla).
The more arid areas are dominated by mulga (Acacia aneura) (Morgan and Terrey 1992). In the north, mulga and poplar box are dominant. In the southwest, poplar box, red box and white cypress pine become more common, and in the far south, poplar box and white cypress pine dominate.
Red ironbark (Eucalyptus sideroxylon), hill red gum (Eucalyptus dealbata) and grey box (Eucalyptus microcarpa) woodlands occur on the eastern edges of the bioregion, extending into the South West Slopes Bioregion. Western vegetation communities dominated by belah (Casuarina pauper), wilga (Geijera parviflora) and rosewood (Alectryon oleifolius) are not well represented. Likewise river red gum (Eucalyptus camaldulensis) and black box (Eucalyptus largiflorens) are limited as there are few large streams in the region. Grasslands are not common in the bioregion.
Mallee is widespread on rocky ridges and sandplains. Typical species include pointed mallee (Eucalyptus socialis), Dwyer's mallee gum (Eucalyptus dwyeri), grey mallee (Eucalyptus morrisii), green mallee (Eucalyptus viridis), mallee broombush (Melaleuca uncinata), hill tea-tree (Leptospermum trivalve), currawang (Acacia doratoxylon), other Acacia sp. and woody shrubs.
Degradation of the Cobar Peneplain Bioregion by heavy grazing has resulted in vast areas being covered by a dense regrowth of woody shrubs (Morgan and Terrey 1992). This shrub layer consists of Eremophila, Dodonaea and Senna spp. which are unpalatable to stock (Creaser and Knight 1996). The encroachment and proliferation of such species is a major problem throughout the semi-arid rangelands of NSW (EPA 1997) and hence these species, although native, are known as woody weeds.
Despite the problems of grazing and woody weeds, the dominant woodlands of the bioregion are both structurally and physically intact. In fact, the woodlands of the Cobar Peneplain Bioregion are the most extensive woodland communities to remain in western NSW (Morgan and Terrey 1992).
Pilaar is the Ngiyampaa name for the belah tree, a significant and special plant to the Pilaarrkiyalu or belah tree people of the Cobar Peneplain (Harris et al. 2000). Pilaarr is a symbol of who the people are and represents their kinship with their ngurrampaa or campworld (Harris et al. 2000).
Mallee woodland communities (Eucalyptus spp.) are widespread throughout the Cobar Peneplain Bioregion, occurring mainly on rocky hills and ridges. Pointed mallee (Eucalyptus socialis) communities mainly occupy the sandplain areas while Dwyer's mallee gum (E. dwyeri) and grey mallee (E. morrisii) occur in shallow soils on crests of ridges in the centre of the bioregion (Cunningham et al. 1981). Green mallee (E. viridis) communities extend between Griffith and Cobar and further east on low ridges (Cunningham et al. 1981).
Despite the diversity of mallee species in the bioregion, as much as 90 per cent of the original mallee communities throughout the Cobar Peneplain Bioregion have been cleared, leaving the remnant mallee stands vulnerable to local extinction (Morton et al. 1995). Mallee is therefore considered to be of high conservation significance in the bioregion.
The Cobar Peneplain Bioregion supports 19 flora species that are listed in the TSC Act (NSW NPWS 2001). Of these, 9 are listed as vulnerable and 9 as endangered, with one species, Osteocarpum pentapterum, presumed extinct in NSW (TSC Act 1995).
Several species found in the Cobar Peneplain Bioregion are listed as vulnerable in the Commonwealth EPBC Act 1999. These include Bertya "opponens", a member of the Bertya genus found in mallee communities on shallow soils on ridges in the Cobar-Coolabah area (Bowen and Pressey 1993). The curly-bark wattle (Acacia curranii) is also found and occurs only in the Cobar Peneplain Bioregion (NSW NPWS 2001).
The Cobar greenhood orchid Pterostylis cobarensis is regionally endemic to the bioregion and is listed as vulnerable in both the TSC and EPBC Acts (Bowen and Pressey 1993, cited in Morton et al. 1995). It is under threat by both grazing and noxious weed invasion (NSW NPWS 2001).
The winged peppercress (Lepidum monoplocoides) is listed in both the TSC and EPBC Acts as endangered and is found mainly in the Cobar Peneplain Bioregion, although some sightings are recorded in the Darling Riverine Plains Bioregion (NSW NPWS 2001). Six species listed as threatened in the EPBC Act are also found in the bioregion.
Other threatened plants include Lomandra patens, Bothriochloa biloba, Rhodanthe citrina, Monotaxis macrophylla and Goodenia occidentalis as well as Kunzea aff. ambigua, Phebalium obcordatum, and Elachoma hornii, all of which have been described as rare to the region (Morton et al. 1995).
Fauna surveys undertaken during the Cobar Peneplain bioregional assessment found that the major vegetation types were largely indicative of the fauna found there (NSW NPWS 2000b). For example, vegetation type contributed to fairly accurate predictions of the distribution of bird species and particular bird assemblages (Masters and Foster 2000).
Some fauna species are widespread across the bioregion, occurring across all major vegetation types. For example, reptiles include Carnaby's wall skink (Cryptoblepharus carnabyi) and south-eastern morethia (Morethia sp.) which are both fairly widespread west of the Great Dividing Range (Cogger 1992).
The bioregion also supports a range of mammals that inhabit much of the Peneplain such as the short-beaked echidna (Tachyglossus aculeatus), eastern grey kangaroo (Macropus giganteus) and inland mastiff-bat (Mormopterus sp.), as well as many woodland birds such as the blue-faced honeyeater (Entomyzon cyanotis), rainbow bee-eater (Merops ornatus) and mistletoe bird (Diacaeum hirundinaceum).
The kultarr (Antechinomys laniger) is a dasyurid which is known as the "marsupial mouse" due to its large ears, long tail and irregular hopping gait (NSW NPWS 2000b). The distribution of the kultarr has declined in NSW and the species now occurs in a patchy distribution to the west of the Bogan River, which borders the Cobar Peneplain Bioregion (Dickman et al. 1993, cited in Morton et al. 1995). Although the species is not directly affected by human activity, the changes in, or intensification of, land use, is thought to threaten its security (Strahan 1983). The kultarr is now listed as endangered in Schedule 1 of the TSC Act 1995.
The now sparse distribution of the greater long-eared bat (Nyctophilus timoriensis) and yellow-bellied sheathtail bat (Saccolaimus flaviventris) can be mainly attributed to loss of habitat. These bats rely on trees for roosting and the absence of sufficient vegetation has rendered them at risk of predation by cats (Dickman et al. 1993, cited in Morton et al. 1995). Both species are listed as vulnerable in Schedule 2 of the TSC Act 1995.
The bird species of the bioregion are fairly typical of semi-arid climatic zones, although this bioregion is unusual in that it contains a higher than average proportion of endemic Australian bird species, a reflection of its regionally distinct dry climate. Declines of these species in the small areas of woodland in the bioregion are likely to continue unless adequate representative areas of woodland are protected from clearing and over-grazing.
Despite the scarcity of remnant mallee stands in the bioregion this vegetation supports significant populations of the also vulnerable (TSC Act 1995) striated grasswren (Amytornis striatus striatus) (Garnett 1992, cited in Morton et al. 1995). The shining bronze-cuckoo (Chrysococcyx lucidus) and speckled warbler (Sericornis sagittatus or Chthonicola sagittata) also rely on these small remnants, and are considered to be in decline in the bioregion (Smith et al. 1994, cited in Morton et al. 1995).
There are 43 faunal species listed as threatened under Schedules 1 and 2 of the TSC Act 1995 (Smart et al. 2000b). Thirty-six of these are listed as vulnerable and 7 are listed as endangered. Although not formally listed in legislation, other fauna species (64 birds, 12 mammals, 23 reptiles and 8 frogs) are identified as being of conservation concern because their numbers are declining or they are locally extinct within the bioregion (NSW NPWS 2000a).
Of the 88 mammal species found in the Western Division at the time of European settlement, 27 were thought to be regionally extinct by the 1990s (Main 2000). In the Cobar Peneplain Bioregion these species include the bilby (Macrotis lagotis) and the bridled nail-tail wallaby (Onychogalea fraenata), both formerly found in the bioregion and now listed as species presumed extinct in NSW under Schedule 1 Part 4 of the TSC Act 1995.
In addition to the various native animals that typically inhabit the Cobar Peneplain, many feral animals are now commonly seen throughout the bioregion. Of the mammals in the bioregion, domestic livestock, goats, rabbits and foxes were the most conspicuous during surveys (NSW NPWS 2000b). Such species as the fox (Vulpes vulpes) are becoming more widespread through western NSW and together with cats (Felis catus) prey on the native species of the bioregion (NSW NPWS 2000b).
Lake Brewster is the only wetland of national significance in the bioregion. Considered to be in fair condition, the status of this wetland is declining due to threats by European carp and other feral animals, exotic weeds and altered hydrology. Despite these disturbances, the lake remains an important refuge habitat for water birds as it retains water longer than nearby natural lakes during drought.
Lake Cargelligo is the only bioregionally significant wetland wholly within the Cobar Peneplain. It is described as being in fair condition, affected somewhat by feral animals, exotic weeds, increased water flows and grazing pressure.
The site is important for several vulnerable species including brolga (Grus rubicundus), freckled duck (Stictonetta naevosa), Major Mitchells cockatoo (Cacatua leadbeateri), blue-billed duck (Oxyura australis), black-breasted buzzard (Hamirostra melanosternon) and western blue-tongued lizard (Tiliqua occipitalis). The endangered malleefowl (Leipoa ocellata) has also been sighted at the lake.
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Page last updated: 27 February 2011