Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion - critically endangered ecological community listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list 'Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion', as a CRITICALLY ENDANGERED ECOLOGICAL COMMUNITY in Part 2 of Schedule 1A of the Act. Listing of Critically Endangered Ecological Communities is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion is the name given to the ecological community characterised by the species assemblage listed in paragraph 2. In NSW all sites are within the Broken Hill Complex Bioregion sensu Thackway & Cresswell (1995). This community is fully congruent with Benson's (2008) 'ID 359: Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland on metamorphic ranges on the Barrier Range, Broken Hill Complex Bioregion'.

2. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion is characterised by the following assemblage of species:

3. The total species list of the community is considerably larger than that given above, with many species present in only one or two sites or in low abundance. The species composition of a site will be influenced by the size of the site, recent rainfall or drought condition and by its disturbance (including fire) history. The number of species, and the above ground relative abundance of species will change with time since fire, and may also change in response to changes in fire regime (including changes in fire frequency). At any one time, above ground individuals of some species may be absent, but the species may be represented below ground in the soil seed banks or as dormant structures such as bulbs, corms, rhizomes, rootstocks or lignotubers. The list of species given above is of vascular plant species; the community also includes micro-organisms, fungi, cryptogamic plants and a diverse fauna, both vertebrate and invertebrate. These components of the community are poorly documented.

4. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion typically forms an open hummock grassland with or without a low sparse woodland canopy. This community is characterised by an unusual co-occurrence of Red Mallee (Eucalyptus socialis) and Gum Coolabah  (Eucalyptus intertexta), growing as scattered trees in a landscape dominated by Porcupine Grass  (Triodia scariosa subsp.  scariosa) on rocky ranges. All three species, especially the eucalypts, are normally plants of plains or sand-dune country and rarely occur on rocky range substrates in NSW. Their presence on such ranges is likely to be a result of the aeolian soil layer. Shrubs are very sparse and include Mulga  (Acacia aneura  sens lat.), Prickly Wattle  (Acacia victoriae subsp.  arida), Dead Finish  (Acacia tetragonophylla), Black Bluebush  (Maireana pyramidata), Ruby Saltbush  (Enchylaena tomentosa), Silver Cassia  (Senna artemisioides) and Bladder Saltbush  (Atriplex vesicaria). Ground cover additional to the  Triodia includes Silver Tails  (Ptilotus obovatus var.  obovatus), Frosted Goosefoot  (Chenopodium desertorum),  Sida  petrophila, Lemon Grass  (Cymbopogon ambiguous), Thargomindah Nightshade  (Solanum sturtianum), Rock Fern  (Cheilanthes sieberi subsp.  sieberi), Native Carrot  (Daucus  glochidiatus), Angular Saltbush  (Atriplex angulata), Jointed Nineawn  (Enneapogon cylindricus) and Limestone Copperburr  (Sclerolaena obliquicuspis).

5. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion occurs (Benson 2008) on rocky hills in the Umberumberka Range section of the Barrier Range, north of Silverton, in the Unincorporated area. It occurs on thin red sandy loam soils of primarily aeolian origin, deposited (possibly during the last glacial maximum) over rocky outcrops of the Willyama complex, composed of Proterozoic gneiss, phyllite, schist, sandstone and slate. Fire is likely to be infrequent.

6. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion is not known to occur in any conservation reserves and is known only from leasehold lands. It occupies a total area estimated at 400 ha +/- 30% (Benson 2008; Sass et al. in press), in two main areas of about 300 ha and 200 ha, each with some natural fragmentation. Benson (2008) assesses this as a naturally very highly restricted community and estimates decline since European settlement as of the order of 20%.

7. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion is "possibly similar to [the South Australian] Floristic Group 9, Eucalyptus socialis open tree mallee, in Playfair & Robinson (1997) but the South Australian community lacks  Triodia" (Benson 2008). It may grade into Bluebush and Saltbush communities on adjacent lower slopes and plains, and on higher ground into more widespread hill Mulga communities such as Dead Finish - Mulga Shrubland (ID 123 of Benson 2008), and Curly Mallee open woodland (ID 169); the latter has a ground layer not dominated by  Triodia.

8. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion is habitat for a reptile fauna that includes the Slender Mallee Blue Tongue Lizard (Cyclodomorphus melanops elongatus), the Marble-faced Delma  (Delma australis), and the Tawny Crevice-dragon  (Ctenophorus decresii), all listed as Endangered under the  Threatened Species Conservation Act 1995. This ecological community represents an extension of habitat and range for the first two of these species, which were previously known only from  Triodia vegetation on sandplain or sand-dune substrates (Sass  et al. in press). It provides a similar extension of habitat for the widespread and  Triodia-dependent Unbanded Delma  (Delma butleri) which usually occurs on sandy substrates, and the local population of this species is thought to be disjunct from the nearest occurrence, at Coombah Station, by about 140 km (Sass  et al. in press). The region in which this ecological community occurs is also known habitat for a number of listed threatened mammal and bird species (NGH Environmental 2008), but their utilisation of this specific community is not yet documented.

9. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion may have undergone past disturbance including cutting of trees for use in fencing and local towns and mines. Porcupine Grass (Triodia) is likely to be a crucial component of ecological function for this community, and also an important element in retaining the thin aeolian soil layer; any processes leading to widespread loss of Porcupine Grass hummocks, or loss of soil or changes in soil nutrient fluxes, are likely to be a significant threat to the community as a whole. Significant areas of die-off of  Triodia and of tree species were noted in 2009 during severe drought (J. Benson, Sass  et al. in press; NGH Environmental 2008), with no evidence of recent regeneration of tree species (Sass  et al. in press). The community is threatened by continuing grazing and browsing by feral goats, with this identified as a likely major contributing reason for the lack of apparent recruitment of the tree and shrub species (Benson 2008; Sass  et al. in press). Goats also threaten particular crevice-sheltering reptiles, such as the Tawny Crevice-dragon, through the filling of rock crevices with goat scats (Sass  et al. in press). 'Competition and habitat degradation by Feral Goats,  Capra hircus Linnaeus 1758' is listed as a Key Threatening Process under the  Threatened Species Conservation Act 1995. Browsing by domestic stock, including newly adopted breeds of sheep with a propensity for browsing such as dorpas and damaras (J. Pickard  in litt. April 2008), is a potential threatening factor for the community. A potential threat, now much reduced (J. Benson pers. comm. Nov. 2009), was proposed works associated with a wind farm (Silverton Windfarm Developments 2008; NGH Environmental 2008). Construction and maintenance of remaining works will however have some direct impact, and there is a risk that roads and construction sites will act as colonisation routes for weeds (J. Pickard  in litt. 2008) and possibly feral animals. Reduced rainfall and higher temperatures and evaporative rates associated with climate change may affect the community; 'Anthropogenic Climate Change' is listed as a Key Threatening Process under the  Threatened Species Conservation Act 1995. The community has a low incidence of weeds as yet, with only the aggressive perennial weed Rosy Dock  (Acetosa vesicaria) recorded by Benson (2008), but NGH Environmental (2008) notes the presence in the community of the introduced Winged Sea Lavender  (Limonium lobatum), Common Sow-thistle  (Sonchus oleraceus), and Wards Weed  (Carrichtera  annua), and the occurrence in nearby communities of a range of potentially significant weeds including the Sea Lavender, African Boxthorn ( Lycium  ferocissimum), and the introduced annual grasses Roughtail  (Rostraria pumila), and Arabian Grass  (Schismus barbatus).

10. Porcupine Grass - Red Mallee - Gum Coolabah hummock grassland / low sparse woodland in the Broken Hill Complex Bioregion is eligible to be listed as a Critically Endangered Ecological Community as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future, as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

Clause 26

The ecological community's geographic distribution is estimated or inferred to be:

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal Date: 24/09/10
Exhibition Period: 24/09/10 - 19/11/10

References:

Benson JS (2008) New South Wales vegetation Classification and Assessment: Part 2 Plant communities of the NSW South-western Slopes Bioregion and update of NSW Western Plains plant communities, version 2 of the NSWVCA database. Cunninghamia 10, 599-673.

NGH Environmental (2008) Proposed development of Stage 1, Silverton Wind Farm, far western New South Wales. Biodiversity Addendum-Final, November 2008. Bega, NSW. Accessed 12 Nov. 2009.

Playfair R M, Robinson A C (1997) (eds.) A biological survey of the North Olary Plains, South Australia 1995-1997. (Natural Resources Group, Department of Environment and Natural Resources: South Australia)

Sass S, Swan G, Marshall B, Browne T, Graham-Higgs N (in press) Disjunct populations of Spinifex-obligate reptiles revealed in a newly described vegetation community near Broken Hill, far-western New South Wales. Australian Zoologist)

Silverton Windfarm Developments (2008) Environmental Assessment. Accessed 12 Nov. 2009.

Thackway R, Creswell ID (1995) An interim biogeographic regionalisation for Australia: a framework for setting priorities in the National Reserve System Cooperative Program. (Version 4.0. ANCA: Canberra.)