Acacia melvillei Shrubland in the Riverina and Murray-Darling Depression bioregions - endangered ecological community listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list Acacia melvillei Shrubland in the Riverina and Murray-Darling Depression bioregions as an ENDANGERED ECOLOGICAL COMMUNITY in Part 3 of Schedule 1 of the Act. The listing of Endangered Ecological Communities is provided for by Part 2 of the Act.

NSW Scientific Committee - final determinations

The Scientific Committee has found that:

1. Acacia melvillei Shrubland in the Riverina and Murray-Darling Depression bioregions is the name given to the ecological community that is dominated by  Acacia melvillei and typically occupies sandhills and undulating sandplains in south-western NSW. In both bioregions, the community occurs on red-brown, sandy loam soils as scattered patches grading into surrounding woodlands of Belah and Rosewood, White Cypress Pine or sandplain mallee.  Acacia melvillei Shrubland is characterised by the assemblage of species listed in paragraph 2 and typically has an open canopy of shrubs or small trees, sometimes with scattered mid-stratum shrubs, and with a sometimes sparse, but highly variable ground layer dominated by grasses, chenopods and herbs. The structure and species composition of the community varies depending on disturbance history and temporal variability in rainfall.

2. Acacia melvillei Shrubland is characterised by the following assemblage of species:

3. The total species list of the community is 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 conditions and by its disturbance (including grazing, land clearing and fire) history. The number and relative abundance of species will change with time since fire, and may also change in response to changes in fire frequency or grazing regime. At any one time, above-ground individuals of some species may be absent, but the species may be represented below ground in soil seed banks or as dormant structures such as bulbs, corms, rhizomes, rootstocks or lignotubers. The list of species given above is mainly of vascular plant species, however the community also includes micro-organisms, fungi, cryptogamic plants and both vertebrate and invertebrate faunas. These components of the community are poorly documented.

4. Acacia melvillei Shrubland is characterised by an open stratum of large shrubs or small trees, which may be reduced to isolated individuals or may be absent as a result of past clearing. The shrub/tree layer is dominated by  Acacia melvillei (Yarran), either in pure stands or with a range of other less abundant trees or tall shrubs. These may include  Acacia loderi (Nelia),  Alectryon oleifolius subsp.  canescens (Rosewood),  Casuarina pauper (Belah) and/or  Myoporum platycarpum (Sugarwood). A scattered small shrub layer is sometimes present and may include  Enchylaena tomentosa (Ruby Saltbush),  Eremophila sturtii,  Nitraria billardierei (Dillon bush),  Rhagodia spinescens (Thorny Saltbush) and/or  Maireana pyramidata (Black bluebush). The groundcover is highly variable in structure and composition. It may be sparse or more continuous, depending on the history of disturbance, grazing and rainfall events. It comprises chenopod subshrubs such as  Atriplex stipitata,  Dissocarpus paradoxus (Cannonball Burr),  Maireana spp.,  Sclerolaena spp. (Copperburrs),  Einadia nutans subsp.  nutans (Climbing Saltbush) and grasses and forbs including  Austrostipa nitida,  Crassula colorata,  Erodium crinatum (Blue Storksbill),  Tetragonia tetragonioides.  Triraphis mollis and  Zygophyllum  ammophilum (Sand Twinleaf). The structure of the community varies depending on past and current disturbances, particularly clearing, logging, grazing and soil erosion and on the timing and magnitude of recent rainfall.

5. Acacia melvillei Shrubland shares a number of species with  Acacia loderi Shrublands, another ecological community currently listed as Endangered under the  Threatened Species Conservation Act 1995. These two ecological communities inhabit similar soils and landforms and have some overlap in their distributions, but  Acacia loderi Shrublands are more common in the northern part of the Riverina and Murray-Darling Depression bioregions and extend further north into several other bioregions. They may be distinguished on the basis of the relative abundance of their tree species (with  A. melvillei generally uncommon within  Acacia loderi shrublands) and differences in composition of their understories. Differences in understorey composition may be obscured as a result of the history of heavy disturbance throughout both communities.  Acacia melvillei is very difficult to distinguish from the closely related species  Acacia homalophylla. Kodela (2001) reviewed herbarium specimens of both species to provide information on their distribution. Both species were found to be widespread in NSW with overlapping distributions. To reliably identify the species in the field, the presence of seed pods is required (Kodela 2001).

6. A number of vegetation surveys and mapping studies have been carried out in regions within which Acacia melvillei Shrubland occurs. The community includes: ‘ Acacia melvillei Woodland’ (Map unit 17) of Scott (1992), Porteners (1993) and Porteners  et al. (1997); ‘ Acacia melvillei Yarran tall open-shrubland’ (Community 3b) of Westbrooke & Miller (1995); ‘ Acacia melvillei / Acacia homalophylla woodlands on sandy rises’ of Horner  et al. (2002); and ‘Yarran shrubland of the sandplains and plains of the semi-arid (warm) and arid climate zones’ (Veg. Comm. ID 23) of Benson  et al. (2006).  Acacia melvillei Shrubland belongs to the Riverine Sandhill Woodlands vegetation class of Keith (2004).

6. Acacia melvillei Shrubland is currently recorded from south-western portion of NSW in the Riverina and Murray-Darling Depression bioregions in the local government areas of Balranald, Carrathool, Central Darling, Conargo, Wakool and Wentworth. The community may occur elsewhere in the Riverina and Murray-Darling Depression bioregions, particularly in the Hay and Jerilderie local government areas. Bioregions are defined by Thackway & Creswell (1995).

7. Acacia melvillei Shrubland is scattered over a relatively large distribution, with an estimated extent of occurrence in the order of 50000km2. Throughout this distribution,  Acacia melvillei Shrubland occurs in relatively small patches. Vegetation maps (1:250000 scale) by Scott (1992), Porteners (1993) and Porteners  et al. (1997) delineate about 500ha of the community as ‘ Acacia melvillei Woodland’ (map unit 17) and a further 5200ha of mosaics containing patches of this community with other types of vegetation. These maps cover most of the community’s distribution. Within the eastern part of this region, Horner et al. (2002) mapped approximately 1400ha of the community as ‘ Acacia melvillei /  Acacia homalophylla woodlands on sandy rises’. Based on available mapping and site records, and using a grid scale of 4km2 (as recommended by IUCN 2006),  Acacia melvillei Shrubland is estimated to occupy an area of about 800 km2. This latter estimate indicates that the community has a moderately restricted distribution.

8. Acacia melvillei Shrubland is generally not found on soils of high suitability for agriculture. However, some stands of the community are threatened by clearing for cropping, particularly in the east of its range (Porteners 1993, Benson  et al. 2006). 'Clearing of native vegetation' is listed as a Key Threatening Process under the  Threatened Species Conservation Act 1995.

9. Most of the remaining stands of Acacia melvillei Shrubland are heavily degraded by overgrazing, which has resulted in simplification of community structure, changes in species composition, invasion of weeds and soil erosion (Eldridge and Greene 1994, Eldridge 1998, Benson  et al. 2006). Overgrazing by domestic livestock and feral herbivores, including rabbits and goats, has resulted in a scarcity of woody understorey plants and a lack of regeneration of palatable trees and shrubs in the community (Batty and Parsons 1992, Porteners 2001, Benson  et al. 2006, Enke 2007). Consequently, senescent trees are not replaced with new individuals and there is a prolonged trend of stand degeneration, which is difficult to reverse, even under active conservation management (Dayman 2007, Enke 2007). Overgrazing also reduces structural complexity, plant species diversity and habitat suitability for vertebrate fauna of the community. Collectively, the processes associated with overgrazing have resulted in a large reduction in the ecological function of the community. 'Competition and grazing by the feral European Rabbit,  Oryctolagus cuniculus' and 'Competition and habitat degradation by Feral Goats,  Capra hircus' are listed as Key Threatening Processes under the  Threatened Species Conservation Act 1995.

10. Fragmentation, grazing and small-scale physical disturbance have resulted in weed invasion throughout the distribution of Acacia melvillei Shrubland, which continues to threaten the ecological function of the community. Principal weed species include:

11. Examples of Acacia melvillei Shrubland have been recorded from Mungo and Willandra National Parks, and Kajuligah and Yanga Nature Reserves (Westbrooke and Miller 1995; Porteners 2001, Benson  et al. 2006). However, some of these reserves contain only a few hectares of the community, and all exhibit signs of degradation associated with past land uses and the continuing impacts of feral herbivores.

12. Acacia melvillei Shrubland of the Riverina and Murray-Darling and NSW South Western Slopes bioregions is not eligible to be listed as a critically endangered ecological community.

13. Acacia melvillei Shrubland of the Riverina and Murray-Darling Depression and NSW South Western Slopes bioregions is eligible to be listed as an endangered ecological community as, in the opinion of the Scientific Committee, it is facing a very high risk of extinction in New South Wales in the near future, as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

Clause 27

The ecological community has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time span appropriate to the life cycle and habitat characteristics of its component species:

(b) a large reduction in ecological function, as indicated by the following:

(d) change in community structure

(e) change in species composition

(f) disruption of ecological processes

(g) invasion and establishment of exotic species

(h) degradation of habitat

Professor Lesley Hughes
Chairperson
Scientific Committee

Proposed Gazettal date: 04/07/08
Exhibition period: 04/07/08 - 29/08/08

References

Batty AL, Parsons RF (1992) Regeneration of Acacia melvillei in part of semi-arid south-east Australia.  Proceedings of the Royal Society of Victoria 104, 89-97.

Benson JS, Allen, CB, Togher C, Lemmon J (2006) New South Wales vegetation classification and assessment. Part 1 Plant communities of the NSW western plains. Cunninghamia 9, 383-450.

Dayman R (2007) Threatened Acacia report. Mungo National Park. NSW National Parks and Wildlife Service, Lower Darling Area, Buronga.

Eldridge DJ (1998). Trampling of microphytic crusts on calcareous soils and its impact on erosion under rain-impacted flow. Catena 33, 221-239.

Eldridge DJ, Greene RSB (1994). Assessment of sediment yield from a semi-arid red earth with varying cover of cryptogams Journal of Arid Environments 26, 221-232.

Enke R (2007) Assessment of Acacia melvillei exclosure Square Mile paddock - Mungo National Park. NSW National Parks and Wildlife Service, Lower Darling Area, Buronga

Horner G, McNellie M, Nott TA, Vanzella B, Scleibs M, Kordas GS, Tuner B, Hudspith TJ (2002) Native vegetation map report series No. 2. Dry lake, Oxley, Hay, One Tree, Moggumbill and Gunbar 1:100 000 map sheets. NSW Department of Land and Water Conservation, Parramatta.

IUCN (2006) Guidelines for using the IUCN Red List Categories and Criteria: Version 6.2. Species Survival Commission, Standards and Petitions Working Group. http://www.iucnredlist.org/info/categories_criteria

Keith DA (2004) 'Ocean shores to desert dunes: the native vegetation of New South Wales and the ACT.' NSW Department of Environment and Conservation, Sydney.

Kodela PG (2001) Identification and review of Acacia melvillei specimens in New South Wales. Report to the NSW Scientific Committee, Sydney.

Porteners MF (1993) Natural vegetation of the Hay Plain: Booligal-Hay and Deniliquin-Bendigo 1:250 000 maps. Cunninghamia 3, 1-122.

Porteners MF (2001) Mungo National Park Threatened Acacia Shrubland survey. Report to NSW National Parks and Wildlife Service Lower Darling Area, Buronga.

Porteners MF, Ashby EM, Benson JS (1997) The natural vegetation of the Pooncarie 1:250000 map. Cunninghamia 5, 139-231.

Scott JA (1992) The natural vegetation of the Balranald-Swan Hill area. Cunninghamia 2, 597-654.

Thackway R, Creswell ID (1995) (eds) 'An interim biogeographic regionalisation of Australia: a framework for establishing the national system of reserves.' Version 4.0 (Australian Nature Conservation Agency: Canberra).

Westbrooke ME, Miller JD (1995) Vegetation of Mungo National Park, western NSW. Cunninghamia 4, 63-81.