Old Man Saltbush Shrubland in western NSW - rejection of endangered ecological community listing
The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to REJECT a proposal to list the Old Man Saltbush Shrubland in western NSW as an ENDANGERED ECOLOGICAL COMMUNITY in Part 3 of Schedule 1 of the Act. Rejection of nominations is provided for by Part 2 of the Act.
NSW Scientific Committee - final determination
The Scientific Committee has found that:
1. Old Man Saltbush Shrubland, as described by vegetation mapping studies in NSW, is characterised principally by the dominance of Atriplex nummularia Lindl. (Old Man Saltbush), a chenopod shrub that grows up to 2.5 metres tall. There is considerable confusion between the existence of an endangered ecological community dominated by Old Man Saltbush, Atriplex nummularia and the individual species itself.
2. In NSW, A. nummularia, as a species, occurs across a range of soil types on level to depressed plains, low-lying areas and depressions (Cunningham et al. 1992; Porteners 1993; Porteners et al. 1997), sometimes being associated with dry lakes (Fox 1991; Scott 1992; Horner et al. 2002; White et al. 2002). In north-west NSW it occurs on alluvial plains that are periodically flooded and on sandy rises adjacent to floodplains (Pickard and Norris 1994). Historical records of A. nummularia distribution disagree as to the extent and abundance of the species across western NSW, leading to many unresolved interpretations (Williams and Oxley 1979). Prevailing opinion among early observers and contemporary ecologists is that the species and its habitats were extensively overgrazed by livestock and rabbits starting in the late 1800s, leading to local extinction and patchiness ( e.g. Moore 1953; Porteners et al. 1997; White et al. 2002). Nonetheless, A. nummularia remains widely distributed, if often locally rare, in western NSW.
3. As a species, Atriplex nummularia is (or was) found as a substratum component or dominant in various vegetation communities in western NSW. These communities include chenopod shrublands in which other Atriplex species are prevalent, such as A. vesicaria (Bladder Saltbush), and woodlands with an overstorey dominated by Eucalyptus largiflorens (Black Box), Eucalyptus coolabah (Coolibah) and Acacia pendula (Weeping Myall or Boree). Some of these woodland assemblages are listed as Endangered Ecological Communities under the Threatened Species Conservation Act 1995, e.g. ‘Myall Woodland in the Darling Riverine Plains, Brigalow Belt South, Cobar Peneplain, Murray-Darling Depression, Riverina and NSW South Western Slopes bioregions’ and ‘Coolibah-Black Box woodland of the northern riverine plains in the Darling Riverine Plains and Brigalow Belt South bioregions.’
4. A large number of species can co-occur with A. nummularia depending on geographic, topographic, edaphic and hydrologic factors. For example, east of Peery Lake A. nummularia is sometimes found with Maireana pyramidata (Black Bluebush), Sclerolaena intricata (Poverty Bush), Sida intricata (Twiggy Sida) and Daucus glochidiatus (Native Carrot) (Westbrooke etal. 2003). On the floodplains of the Darling and Paroo Rivers, A. nummularia is recorded as occurring within a canopy of Eragrostis australasica (Cane Grass) and Muehlenbeckia florulenta (Lignum) and Chenopodium nitrariaceum (Nitre Goosefoot), along with a lower shrub layer composed of Sclerolaena spp. (copperburrs) (Pickard and Norris 1994). Along drainage lines and depressions in this area it also forms localised stands within larger areas dominated by A. vesicaria (Pickard and Norris 1994). A. vesicaria, Enchylaena tomentosa (Ruby Saltbush) and Rhagodia spinescens (Spiny Saltbush) are co-occuring shrub species in the Darling Riverine Plain Bioregion (L. Forward, unpublished). In the Riverina region species such as Einadia nutans (Climbing Saltbush) and Sclerolaena spp. and other Atriplex spp. are more frequently recorded as co-occuring with A. nummularia (Scott 1992; Porteners 1993). Further west around Pooncarie, Maireana pyramidata, Rhagodia spinescens, Atriplex lindleyi and Osteocarpum acropterum var. deminuta (Porteners et al. 1997) are more likely to be encountered. Species found with A. nummularia in Kinchega National Park include Chenopodium nitrariaceum, Sclerolaena divaricata (Tangled Copperburr) and Maireana pyramidata (Fox 1991). A. nummularia can form dense monospecific stands (Cunningham et al. 1992), crowding other species and resulting in low species richness (Beadle 1948).
5. Old Man Saltbush Shrublands are thought to be very dynamic across time and space, ranging from grassland to monocultures of A. nummularia ( e.g. Williams and Oxley 1979; Cunningham et al. 1992). Some authors have proposed that the rapid degradation of Old Man Saltbush communities with the advent of livestock resulted in the development of extensive areas of derived grasslands ( e.g. Moore 1953), whereas others argue that the historical nature of this alteration is far from clear and that some large areas of predominantly grassland may have existed long prior to the decline of Old Man Saltbush ( e.g. McDougall et al. 1993, McDougall 2008). Overgrazing of A. nummularia has also been thought to result in temporary or long-term dominance by less palatable chenopods ( e.g. ‘Nitre Goosefoot shrubland on clays of the inland floodplains’; Benson et al. 2006). However, without a better understanding of community dynamics there is little potential to establish reference conditions for these chenopod shrublands, and therefore to determine historic declines, current status and future threat. Long-term studies, rather than simply more floristic plots, are needed to determine this variation in community structure and species composition.
6. A recent review and classification of vegetation in western NSW (Benson et al. 2006) recognised stands of A. nummularia and co-occurring species including those listed above are currently recognised as two distinct associations known as ‘Old Man Saltbush shrubland in the semi-arid climatic zone in southwestern NSW’ and ‘Old Man Saltbush shrubland in the semi-arid hot and arid climate zones in north-western NSW’. Benson et al. (2006), recognised these associations on the basis of expert opinion derived from available information about occurrence of the species in NSW, field inspections to record associated species at selected locations in NSW and descriptions from other field studies. Some of these studies used numerical analyses of quadrat data to define assemblages dominated by A. nummularia indicating that regional or local assemblages exist, but difficulties arise from their uncertain relationships with one another and with other chenopod assemblages that may represent 'successional' stages in a complex and dynamic mosaic. Vegetation surveys and mapping studies which include descriptions of a similar community dominated or defined by A. nummularia include Beadle’s (1948) sub-formation found throughout western NSW; large areas in southwest NSW and northwest Victoria mapped by Kerr et al. (2000); areas in northwest NSW mapped by Pickard and Norris (1994); and sites in Nearie Lake Nature Reserve and Kinchega National Park mapped by Westbrooke et al. (1997, 2001). Fox (1991) named a similar saltbush community north of Mildura but found it too localised to map. In the Riverina region, the following studies named an Old Man Saltbush community of varying descriptions: Scott (1992), Porteners (1993), Porteners et al. (1997), Roberts and Roberts (2001), Horner et al. (2002), and White et al. (2002). ‘Bladder Saltbush and Old Man Saltbush shrubland’ was identified in the Darling Riverine Plains during bioregional surveys (L. Forward, unpublished).
7. Descriptions of these Old Man Saltbush communities show little concurrence as to which species are characteristically present. Besides A. nummularia itself, only four other species are identified as characteristic in more than one-fifth of descriptions, and even these latter species are represented on less than a third of those lists: Atriplex vesicaria, Chenopodium nitrariaceum, Maireana pyramidata, Rhagodia spinescens. These four species are also widespread components of other vegetation communities in western NSW ( e.g. ‘Low Bluebush - Bladder Saltbush open shrubland of the arid zone’; Benson et al. 2006). Exploratory pattern analyses of species and site associations based on 3157 vegetation quadrats in western NSW also failed to identify an assemblage of co-occurring species that was clearly referrable to available descriptions of Old Man Saltbush Shrubland (Soderquist and Irvin 2008). Historical and ongoing disturbances related to grazing may have an influence on the apparently diffuse character of plant assemblages containing A.nummularia, but a more thorough understanding of the dynamics of the vegetation is required to ascertain their roles.
8. Given the lack of concurrence among field studies in describing the nominated community, limited corroboration emerging from meta-analysis and uncertain temporal relationships between potentially related assemblages, there remains considerable uncertainty about the characteristic features of Old Man Saltbush Shrubland in NSW. An alternative plausible explanation of the available information is that stands of A. nummularia are visually dominant within a broad and a variable complex of chenopod shrublands and associated grasslands. The lack of clear definition has led to long-standing and unresolved debates among observers who believe that very few patches of Old Man Saltbush Shrubland remain, and those who claim that extensive tracts exist and are recovering.
9. The Scientific Committee made a Preliminary Determination to list Old Man Saltbush Shrubland as an Endangered Ecological Community. This preliminary assessment of the community led to the submission of additional information as to the extent and decline of the nominated community. This in turn necessitated a re-examination and reanalysis of the circumscription of the community. In the light of this analysis, the Committee has determined that there is currently insufficient evidence to draw a robust conclusion about the status of Old Man Saltbush Shrubland in western NSW, as nominated. Without a more adequate understanding of the community composition, dynamics and past distribution it is not feasible to determine if Old Man Saltbush Shrubland in western NSW, as nominated, has undergone a large reduction in distribution or ecological function, or is now highly restricted. Hence there is currently insufficient understanding to assess whether such a community is eligible for listing as an Endangered Ecological Community.
10. In view of the above, the Scientific Committee finds that the nominated Old Man Saltbush Shrubland in western NSW is not currently eligible to be listed as an Endangered Ecological Community in Part 3 of Schedule 1 of the Act.
Professor Lesley Hughes
Chairperson
Scientific Committee
Proposed Gazettal date: 19/12/08
Exhibition period: 19/12/08 – 27/02/09
References
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