Newnes Plateau Shrub Swamp in the Sydney Basin Bioregion - endangered ecological community listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list Newnes Plateau Shrub Swamp in the Sydney Basin Bioregion, as an ENDANGERED ECOLOGICAL COMMUNITY in Part 3 of Schedule 1 of the Act. Listing of endangered ecological communities is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list Newnes Plateau Shrub Swamp in the Sydney Basin Bioregion, as an ENDANGERED ECOLOGICAL COMMUNITY in Part 3 of Schedule 1 of the Act. Listing of endangered ecological communities is provided for by Part 2 of the Act.

The Scientific Committee has found that:

1. Newnes Plateau Shrub Swamp in the Sydney Basin Bioregion is the name given to the ecological community dominated by shrubs and sedges that occurs on sites with impeded drainage in low slope headwater valleys on the Newnes Plateau in the upper Blue Mountains.

2. Newnes Plateau Shrub Swamp 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, and a diverse fauna, both vertebrate and invertebrate. These components of the community are poorly documented.

4. Newnes Plateau Shrub Swamp occurs in narrow, elongated swamps formed in low-slope headwaters of the Newnes Plateau, in predominantly sandstone catchments of Triassic Narrabeen Group geology, at approximately 900-1200 m elevation on deep sandy organic sediments that are permanently to periodically waterlogged.

5. Newnes Plateau Shrub Swamp is characteristically dominated by shrubs, with a variable cover of sedges. Shrubs have a dense to open cover, and include Baeckea linifolia, Grevillea acanthifolia subsp . acanthifolia, Epacris paludosa and  Leptospermum species. The cover of sedges varies inversely with shrub cover. Common sedges include  Baloskion australe, Empodisma minus, Lepyrodia scariosa and  Lepidosperma limicola, while herbs include  Patersonia fragilis and  Xanthosia dissecta.  Gleichenia dicarpa and  Gymnoschoenus sphaerocephalus may occur around drainage lines, while  Lomandra longifolia may be prominent around the swamp margins. Floristic composition varies locally in relation to soil moisture gradients within the swamps (Keith and Benson 1988; Benson and Keith 1990).

6. With decreasing altitude, Newnes Plateau Shrub Swamp grades into Blue Mountains sedge swamp communities (Keith and Benson 1988). The transition occurs around Bell and Clarence at approximately 850-950 m above sea level. Blue Mountains sedge swamps typically have less cover of shrubs and a greater cover of sedges (particularly Gymnoschoenus sphaerocephalus) than Newnes Plateau Shrub Swamp . Other salient features that distinguish Newnes Plateau Shrub Swamp from Blue Mountains sedge swamps include the presence of species in the former such as  Dillwynia stipulifera and  Boronia deanei, the absence from the former of a range of shrub species that are not found at higher altitudes, and the occurrence of the former on subdued terrain, compared with the steep seepage slopes and headwater valleys that typify swamp habitats at lower elevations in the Blue Mountains.

7. Newnes Plateau Shrub Swamp may share a number of characteristics with Montane Peatlands and Swamps of the New England Tableland, NSW North Coast, Sydney Basin, South East Corner, South Eastern Highlands and Australian Alps bioregions, also listed as an Endangered Ecological Community under the Threatened Species Conservation Act (1995). However, this latter community has a lower diversity of sclerophyllous shrub species, a greater diversity of soft-leaved sedges, grasses and herbs, and typically occurs on more fertile substrates than Newnes Plateau Shrub Swamp.

8. Newnes Plateau Shrub Swamp provides habitat for threatened species including Boronia deanei, Petalura gigantea, the Giant Dragonfly, and  Eulamprus leuraensis, the Blue Mountains Water Skink. The endangered shrub,  Persoonia hindii, is also associated with the margins of the swamps.

9. Newnes Plateau Shrub Swamp has been recorded from the local government areas of Lithgow and Blue Mountains City (within the Sydney Basin Bioregion) but may occur elsewhere in the Bioregion. Vegetation mapping of the entire range of Newnes Plateau Shrub Swamp indicates that it covers less than 650 ha in total (Keith and Benson 1988; Benson and Keith 1990). The largest swamp covers about 40 ha, and the average swamp size is less than 6 ha. Approximately 160 ha of Newnes Plateau Shrub Swamp occurs within Blue Mountains and Wollemi national parks, with the remainder on state forest and freehold land. Approximately 120 ha of the community, including the largest swamp, is adjacent to pine plantations or other cleared land.

10. Biogeographically, Newnes Plateau Shrub Swamp is related to other upland swamps in the Sydney Basin (e.g. Keith and Myerscough 1993). It represents the highest altitude expression of upland swamps on sandstone in mainland Australia, and is transitional between the 'Coastal Heath Swamps' and 'Montane Bogs and Fens' vegetation classes of Keith (2004). All of these swamps play important hydrological roles, acting as water filters, releasing water slowly to downstream watercourses, thereby regulating water quality and stream flows (Young and Young 1988).

11. A number of the water catchments containing Newnes Plateau Shrub Swamp contain transport corridors, pine plantations, sand quarries, coal mines or small-scale rural holdings. In some cases, these developments are located immediately adjacent to the swamps or with narrow buffer strips. The community is threatened by small-scale clearing, fragmentation, erosion and sedimentation all associated with roadworks, quarrying and periodic timber harvesting from adjacent plantations. Clearing of native vegetation is listed as a Key Threatening Process under the Threatened Species Conservation Act (1995).

12. Changes to drainage and moisture conditions in some swamps, including the largest example of the community, are caused by damming of swamp watercourses; roading across the swamps; sedimentation and erosion associated with roadways, quarries, mines and plantation harvesting within swamp catchments; and disposal of waste water from underground coal mines. These changes pose threats to the persistence and integrity of Newnes Plateau Shrub Swamp, given the crucial roles of water regimes in the composition, structure and function of the community. Alteration to the natural flow regimes of rivers and streams and their floodplains and wetlands is listed as a Key Threatening Process under the Threatened Species Conservation Act (1995).

13. The Newnes plateau is underlain by extractable coal seams at varying depths, with underground longwall mining occurring, or proposed to occur, beneath the majority of the swamps. Subsidence of the land surface, and associated fracturing of bedrock between the coal seam and the surface, occurs after longwall mining, and this may change the hydrology of catchments and swamps they contain. Specifically, the conversion of perched water table flows into subsurface flows through mine-related voids may significantly alter the water balance of upland swamps (Young and Wray 2000). Changes to surface morphology within or near the swamps as a result of mine subsidence may also create nick points which become the focus of severe and rapid erosion (Young 1982). These changes pose threats to the persistence and integrity of, the community. Alteration of habitat following subsidence due to longwall mining is listed as a Key Threatening Process under the Threatened Species Conservation Act (1995).

14. Invasion of exotic species, including species of Pinus, and changes to fire regimes may pose threats to Newnes Plateau Shrub Swamp in future if any of the above processes result in physical displacement of vegetation, increased influx of sediments and/or nutrients or significant drying of the swamps.

15. In view of the above the Scientific Committee is of the opinion that Newnes Plateau Shrub Swamp in the Sydney Basin Bioregion is likely to become extinct in nature in New South Wales unless the circumstances and factors threatening its survival cease to operate, or it might already be extinct.

Dr Lesley Hughes
Chairperson
Scientific Committee

Proposed Gazettal date: 15/07/05

Exhibition: 15/07/05 - 09/09/05

References

Benson DH, Keith DA (1990) The natural vegetation of the Wallerawang 1:100 000 map sheet. Cunninghamia2 , 305-335.

Keith DA, Benson DH (1988) The natural vegetation of the Katoomba 1:100 000 map sheet. Cunninghamia2 , 107-143.

Keith DA, Myerscough PJ (1993) Floristics and soil relations of upland swamp vegetation near Sydney. Australian Journal of Ecology18 , 325-344.

Young ARM (1982) Upland swamps (dells) on the Woronora plateau, N. S. W. PhD thesis, University of Wollongong.

Young RW, Wray RAL (2000) The geomorphology of sandstones in the Sydney Region. In McNally GH and Franklin BJ eds Sandstone City - Sydney's Dimension Stone and other Sandstone Geomaterials. Proceedings of a symposium held on 7th July 2000, 15th Australian Geological Convention, University of Technology Sydney. Monograph No. 5, Geological Society of Australia, Springwood, NSW. Pp 55-73.

Young RW, Young ARM (1982) 'Altogether barren, peculiarly romantic': the sandstone lands around Sydney. Australian Geographer19 , 9-25.