Myall Woodland - Determination to make a minor amendment to Part 3 of Schedule 1 of the Threatened Species Conservation Act

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Determination to make a minor amendment to Part 3 of Schedule 1 (Endangered ecological communities) of the Act by inserting the Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions (as described in the determination of the Scientific Committee under Division 5 Part 2) and as a consequence to omit reference to the Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions (as described in the final determination to list the ecological community) which was published in the NSW Government Gazette No. 90 dated 15 July 2005 (pages 3732 to 3739) and in the NSW Government Gazette No. 92 dated 22 July 2005 (pages 3798 to 3805). Minor amendments to the Schedules are provided for by Division 5 of Part 2 of the Act.

The Scientific Committee is of the opinion that the amendment is necessary or desirable to correct minor errors or omissions in the Determination in relation to the Thackway and Cresswell (1995) reference.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions is the name given to the ecological community that is scattered across the eastern parts of alluvial plains of the Murray-Darling river system. Typically, the ecological community occurs on red-brown earths and heavy textured grey and brown alluvial soils within a climatic belt receiving between 375 and 500 mm mean annual rainfall. The structure of the community varies from low woodland and low open woodland to low sparse woodland or open shrubland, depending on site quality and disturbance history. The tree layer grows up to a height of about 10 metres and invariably includes Acacia pendula (Weeping Myall or Boree) as one of the dominant species or the only tree species present. The understorey includes an open layer of chenopod shrubs and other woody plant species and an open to continuous groundcover of grasses and herbs. The structure and composition of the community varies, particularly with latitude, as chenopod shrubs are more prominent south of the Lachlan River district, while other woody species and summer grasses are more common further north. In some areas the shrub stratum may have been reduced or eliminated by clearing or heavy grazing.

The community is characterised by the following assemblage of species:

2. The total flora list for 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 the site will be influenced by the size of the site, recent rainfall or drought conditions and by its disturbance (including fire, grazing, flooding and land clearing) history. The number and relative abundance of species will change with time since fire, flooding or significant rainfall, and may also change in response to changes in grazing regimes. 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.

3. Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions is known from parts of the Local Government Areas of Berrigan, Bland, Bogan, Carrathool, Conargo, Coolamon, Coonamble, Corowa, Forbes, Gilgandra, Griffith, Gwydir, Inverell, Jerilderee, Lachlan, Leeton, Lockhart, Moree Plains, Murray, Murrumbidgee, Narrabri, Narranderra, Narromine, Parkes, Urana, Wagga Wagga and Warren, and but may occur elsewhere in these bioregions. Bioregions are defined in Thackway and Cresswell (1995).

4. Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions has an open to sparse tree canopy up to 10 metres tall dominated by Acacia pendula (Myall or Boree), which may occur in pure stands, particularly south of the mid-Lachlan River district, or in combination with other trees such as  Casuarina cristata, Acacia homalophylla (Yarran),  A. oswaldii (Miljee),  Alectryon oleifolius (Rosewood),  Apophyllum anomalum (Warrior bush) and  Capparis spp. The mistletoe,  Amyema quandang, is common on the branches of  Acacia pendula throughout. The shrub layer varies substantially with latitude and grazing history (Beadle 1948), and may be virtually absent in some stands.  Atriplex nummularia (Old man saltbush) was historically one of the dominant understorey shrubs in the south, but is now uncommon in the community (Moore 1953). Other chenopod shrubs, such as  Atriplex semibaccata (Creeping saltbush),  Enchylaena tomentosa (Ruby saltbush),  Maireana aphylla (Cotton bush),  M.decalvens (Black cotton bush),  M. excavata,  M. pentagona (Hairy bluebush),  Rhagodia spinescens (Thorny saltbush) and  Sclerolaena muricata (Black rolypoly), are among the most frequent shrubs in the understorey of Myall Woodland south of the mid Lachlan district. Further north, non-chenopod shrubs, such as  Eremophila maculata (Spotted fuchsia),  Apophyllum anomalum (Warrior bush) and  Atalaya hemiglauca (Whitewood) become more prominent components of the community, although some chenopods may still be common. The ground layer includes a diversity of grasses and forbs, and varies in cover depending on grazing regime and occurrence of recent rain.  Chloris truncata (Windmill grass),  Einadia nutans (Climbing saltbush),  Enteropogon acicularis (Curly windmill grass),  Rhodanthe corymbiflora (Small white sunray),  Solanum esuriale (Quena) and  Sporobolus caroli (Fairy grass), are frequent throughout the range of the community.  Astrebla spp. (Mitchell grasses),  Austrostipa aristiglumis (Plains grass),  Dichanthium sericeum (Queensland bluegrass) and  Panicum decompositum (Native millet) frequently occur in Myall Woodland north from the mid-Lachlan River district, while  Austrodanthonia spp . (White-top or Wallaby grasses) , Austrostipa scabra (Rough speargrass) , and herbs such as  Chrysocephalum apiculatum (Common everlasting),  Goodenia pusilliflora,  Myriocephalus rhizocephalus (Woolly-heads) and  Swainsona spp. (Bladder peas), are more prominent in the south.

5. A number of vegetation surveys and mapping studies have been conducted across the range of Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions. In western New South Wales, the community includes the ‘Acacia pendula Associes’ of Beadle (1948). On the Moree floodplain, the community includes Map unit 7 ‘Myall/Rosewood Woodlands on Elevated Floodplain’ of White (2000) and Map unit 4(b) ‘Myall woodlands’ of DLWC (2002a). In the Lachlan-Macquarie district of central NSW, the community includes the ‘ Acacia pendula-Atriplex nummularia Alliance’ of Biddiscombe (1963), Map unit R5 ‘Myall Woodlands’ of Sivertsen and Metcalfe (1995) and Metcalfe  et al. (2003), Floristic Groups ‘65  Eremophila mitchellii/Acacia oswaldii/A. pendula’, ‘66 Outlier  Acacia homalophylla’, ‘67  Sclerolaena muricata/Acacia pendula’ and ‘68  Acacia pendula’ of Austin  et al. (2000), Map units ALP3 ‘Acacia woodlands of the stagnant alluvial plains:  Acacia pendula’ and ALP4 ‘Acacia woodlands of the stagnant alluvial plains:  Acacia homalophylla’ of DLWC (2002b), and Broad Vegetation Type 5 ‘Myall open-woodland on loamy-clay plains’ of Kerr  et al. (2003). In the Riverina district, the community includes the ‘ Acacia pendula-Atriplex nummularia alliance’ of Moore (1953), Map unit 25  ‘Acacia pendula woodland’ of Porteners (1993), Map Unit 4a ‘Open Boree Woodland/Grassland’ of Roberts and Roberts (2001), Broad Vegetation Type 6 ‘Boree woodland’ of Miles (2001), Map unit 12  ‘Acacia pendula with an herbaceous understorey ’ of DLWC (2002c) and ‘Parna Plains Grassland and Woodland’ of White  et al. (2002). Myall Woodland belongs to the ‘Riverine Plain Woodlands’ vegetation class of Keith (2004).

6. Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions has been substantially reduced and modified by clearing and grazing over the past 160 years. The extent of Myall Woodland has not been mapped across its entire range. However, Riverine Plain Woodlands (which include Myall Woodland), are currently estimated to cover 1000-2000 km², representing less than 30% of the original extent of this broadly defined vegetation class (Keith 2004). Compared to this combined estimate, the remaining area of Myall Woodland is likely to be smaller and is likely to represent much less than 30% of its original range. In the Moree district, White (2001) estimated that 91 km² of Myall/Rosewood Woodlands on Elevated Floodplain remained, representing 8.5% of its estimated pre-clearing distribution. In the lower Macquarie-Castlereagh region, Kerr et al. (2003) estimated that 93% of Myall open woodland had been cleared, leaving less than 300 km² extant. In the Riverina, NSW NPWS (2003) estimated that 94% of Myall Woodland had been cleared, leaving approximately 780 km². In the Murray valley, which partly overlaps the Riverina region, Miles (2001) estimated that 190 km² of Boree Woodland remained, representing only 4% of the pre-clearing distribution.

7. In many areas of the Riverina, Myall Woodland has been eliminated and replaced by a grassland of Chloris,  Austrodanthonia and  Austrostipa, that lacks the woody components of the original woodland vegetation (Beadle 1948, Moore 1953, Porteners 1993, Benson  et al. 1997, Keith 2004). In some areas,  Acacia pendula persists as small, scattered individuals suppressed by grazing. Moore (1953) had considerable difficulty in finding any stands that had not been considerably modified by grazing or clearing, but established the formerly extensive distribution of Myall Woodland in the Riverina from accounts in historical journals and land surveys. Beadle (1948) and Moore (1953) both interviewed local farmers who described a major decline in dominant woody species, particularly  Acacia pendula and  Atriplex nummularia, during droughts of the late nineteenth century when trees were cut for emergency fodder and there was sustained overgrazing by sheep and rabbits. There was also a substantial trade in Myall as firewood (Williams 1962). High levels of grazing also led to the replacement of tall perennial tussock grasses with short perennial grasses and unpalatable annual herbs (Beadle 1948), as well as introduction of exotic herbs and grasses such as  Bromus spp.,  Erodium spp.,  Lepidium africanum, Medicago spp.,  Sisymbrium spp. and  Trifolium spp. Introduced shrubs, notably  Lycium ferocissimum (African boxthorn) have also invaded some areas occupied by the community. Extant remnants of Myall Woodland are therefore in various states of modification that reflect their history of tree removal and grazing.

8. Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions continues to be threatened by clearing and fragmentation associated with cropping, overgrazing by feral and domestic animals, pest outbreaks and weed invasion. In the northern Wheatbelt, for example, the remaining area of Myall Woodland declined by 10% between 1985 and 2000, and more than 90% of the remaining area was in patches less than 10 km² (Cox et al. 2001). Clearing of native vegetation is listed as a Key Threatening Process under the Threatened Species Conservation Act (1995).

9. The dominant species in Myall Woodland, Acacia pendula, is subject to herbivory by the processionary caterpillar  Ochrogaster lunifer (Bag-shelter moth) (NSW Dept. of Agriculture 1960). These caterpillars may cause complete defoliation of the trees. Cunningham  et al. (1981) state that “the severity of defoliation varies from year to year, as does the tree’s reaction. Those stripped of their leaves take a considerable time to recover and in some instances at least, death of the tree occurs as a direct result of catepillar attacks.” The impacts of  O. lunifer are a particular concern to landholders in districts where remnants of Myall Woodland have survived past clearing pressures and where stocking rates are maintained at low levels with the aim of conserving the community.

10. Only a small area of Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions is represented within existing conservation reserves. In the Riverina district, Oolambeyan National Park contains approximately 700 hectares in varying states of recovery, and a further 10 hectares are found in Lake Urana Nature Reserve. Outside the Riverina district, less than 5 ha of Myall Woodland is represented in Macquarie Marshes Nature Reserve.

11. In view of the above the Scientific Committee is of the opinion that Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South western Slopes bioregions is likely to become extinct in nature in New South Wales unless the circumstances and factors threatening its survival or evolutionary development cease to operate.

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal date: 08/07/11
Exhibition period: 08/07/11 - 02/09/11

References

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