Shrublands and woodlands on Perth to Gingin ironstone (Perth to Gingin ironstone association) of the Swan Coastal

Ecological community name

Shrublands and woodlands on Perth to Gingin ironstone (Perth to Gingin ironstone association) of the Swan Coastal Plain.

Description

Plant community located on seasonally inundated ironstone and heavy clay soils on the eastern side of the Swan Coastal Plain. The community supports a rich layer of herbaceous annuals under a sparse shrub layer. The community has been assessed by the WA Threatened Ecological Communities Advisory Committee as Critically Endangered.

Listed Species in the proposed ecological community

Grevillea curviloba subsp. incurva.

Other native species that could become endangered in the proposed ecological community

None known.

Description of the 'Shrublands and woodlands on Perth to Gingin ironstone' (Perth to Gingin ironstone association) of the Swan Coastal Plain' community sufficient to distinguish it from any other ecological community

The ironstone soils are extremely restricted in distribution on the Swan Coastal Plain. These soils may have been historically associated with bogs - the iron being deposited by water percolating through the soil. Restricted areas of ironstone soils associated with unusual plant communities occur in a number of areas in the southwest of Western Australia; near Kalbarri, near Eneabba (Griffin et al., 1983), at Gingin and Busselton (DEP, 1996; Gibson et al., 1994), and in the Scott River area. Each of these areas support identifiable plant communities that are characterised by different taxa.

The Perth to Gingin ironstone soil type occurs on the eastern side of the Swan Coastal Plain. This area contains heavy soils that are particularly useful for agricultural purposes and are around 97% cleared (CALM 1990; Keighery and Trudgen 1992).

Occurrences of the community are all located on the shallow groundwater aquifer, the north Gnangara Mound. The height of the groundwater table is 60-70 metres above sea level (m AHD) where the community occurs. Occurrences are specifically located in a low point adjacent to a peak in the water mound (a 'col') and adjacent to a flow channel in the groundwater mound (Davidson 1995). Local hydrogeology is therefore likely to be very important in maintaining the community.

Long term observations indicate that seasonal inundation is limited to very shallow surface water during the winter months. Inundation usually persists for a period of around three months, with the soils drying out at the surface in summer. The surface waters may be linked to the watertable as the groundwater is close to the surface in September-October (Davidson 1995). Surface water would also originate from rainfall runoff in the wetter months of the year and be retained by the impervious substrata of heavy soils and rock. If there are connections between the surface and groundwater through the ironstone, then both these sources would effect the quantity and quality of water on the surface of the site.

The plant community on these ironstone soils is the only one in the Perth area that is characterised by massed everlastings in the understorey (English et al. 1996). Floristic analyses of plots on this soil type link to 'herb rich shrublands in clay pans' (community type 8) as described by Gibson et al. (1994) - reflecting the clays in the soil (DEP 1996). Typical and common native species in the community are the shrubs Kunzea aff. recurva, Grevillea curviloba subsp. incurva, Melaleuca viminea, Acacia saligna, Jacksonia furcellata, Grevillea obtusifolia and Dryandra sessilis and the herbs Rhodanthe manglesii, Tribonanthes australis and Isotropis cuneifolia subsp. glabra ms. The following exotic species are also currently common; Romulea rosea, Briza maxima, Trifolium dubium, Spergula arvensis and Hesperanthura falcata (DEP 1996).

Many of the plant species present are specifically adapted to this shallow seasonal inundation eg. Kunzea aff. recurva (swamp kunzea). In addition, the herb layer, which is a major distinguishing characteristics of this community, probably would not occur in late winter and early spring, without the incidence of inundation in winter.

It is also unlikely that the daisy dominated herb layer that occurs in spring would occur in deeper soils, as species that reproduce by means other than annual seed production may have a competitive advantage. Indeed, the herb layer on the ironstone soils where the topsoil is deepest is not dominated by daisies, although daisies still occur.

Evidence that the description of the 'Shrublands and woodlands on Perth to Gingin ironstone' (Perth to Gingin ironstone association) of the Swan Coastal Plain' community is conventionally accepted

References and data which support the classification of this community are found in the minutes of the WA Threatened Ecological Communities Advisory Committee dealing with the assessment of this community, in the draft interim recovery plan for the community and in the following publications.

Department of Environmental Protection (1996). System 6 update program unpublished site and area records and analysis. EPA, Perth, Western Australia.

English, V., Keighery, G., Blyth, J. (1996). Threatened Plant Communities on the Swan Coastal Plain. Landscope. 12; 1 pp 35-40.

Gibson, N., Keighery, B., Keighery, G., Burbidge, A and Lyons, M. (1994). A floristic survey of the Southern Swan Coastal Plain. Unpublished report for the Australian Heritage Commission prepared by the Department of Conservation and Land Management and the Conservation Council of Western Australia (Inc.).

Reasons why the 'Shrublands and woodlands on Perth to Gingin ironstone' (Perth to Gingin ironstone association) of the Swan Coastal Plain' community is considered to be endangered within the meaning of Section 6 of the Act

This community fits criteria 2 (a), (c), (d) and (e) for the following reasons.

1. The Community is geographically restricted, has been reduced at least 90% (probably 97%) by clearing, mainly for agricultural purposes, and is now restricted to a total area of about 60ha.
2. All the remainder was on private land. Acquisition and reservation of the largest and best remaining example was completed in 1999, using funds from the Natural Heritage Trust and the Western Australian government.
3. Remaining patches have a history of grazing and other disturbances and are threatened by clearing, weed invasion, and potential hydrological changes including secondary salinisation. Grazing by cattle, if continued, would continue to modify the community.

Past and current distributions of the 'Shrublands and woodlands on Perth to Gingin ironstone' (Perth to Gingin ironstone association) of the Swan Coastal Plain' community

On the 1:50,000 scale Urban/Environmental Geology series (Anon 1976, 1977; Gozzard 1982) ironstone areas are noted as "bog-iron or iron-rich laterite" within the Guildford Formation, which consists mainly of alluvial clays. The original extent of the community is not known as boundaries of the soil type are not specified on these maps. It is evident however, that the soil type is extremely restricted and that most (>97%) of the original community has now been cleared (Gibson et al. 1994).

References that support information given in the nomination

Anon (1976). Gingin Sheet 3035 II. Urban Geology Series. Geological Survey of Western Australia. Department of Minerals and Energy, Perth.

Anon (1977). Moore River - Cape Leschenault Sheet 2035 III and part Sheet 1935. Urban Geology Series. Geological Survey of Western Australia. Department of Minerals and Energy, Perth.

Churchward, H.M. and McArthur (1980). Landforms and Soils of the Darling System. In: Atlas of Natural Resources, Darling System, Western Australia. Perth Sheet. Department of Conservation and Environment, Western Australia.

Davidson, W.A. (1995). Hydrogeology and Groundwater Resources of the Perth Region, Western Australia. Geological Survey of Western Australia. Bulletin 142.

Department of Conservation and Land Management (1990). Data on the Conservation of Vegetation Associations on the Swan Coastal Plain. Unpublished Report.

Department of Conservation and Land Management (1997). Declared Rare and Priority List for Western Australia. Department of Conservation and Land Management, Perth.

Department of Environmental Protection (1996). System 6 update program unpublished site and area records and analysis. EPA, Perth, Western Australia.

English, V. and Blyth, J. (1997). Identifying and Conserving Threatened Ecological Communities in the South West Botanical Province. Project N702, Final Report to Environment Australia. Department of Conservation and Land Management. Perth, Western Australia.

English, V., Keighery, G., Blyth, J. (1996). Threatened Plant Communities on the Swan Coastal Plain. Landscope. 12; 1 pp 35-40.

Gibson, N., Keighery, B., Keighery, G., Burbidge, A and Lyons, M. (1994). A floristic survey of the Southern Swan Coastal Plain. Unpublished report for the Australian Heritage Commission prepared by the Department of Conservation and Land Management and the Conservation Council of Western Australia (Inc.).

Gill, A.M., Groves, R.H. and Noble, I.R. (eds) (1981). Fire and the Australian Biota. Australian Academy of Science. Canberra, ACT.

Gozzard, J.R. (1982). Muchea Sheet 2034 I and part Sheet 2134 IV, Environmental Geology Series. Geological Survey of Western Australia. Department of Minerals and Energy, Perth.

Greay, J. (1993). Yanchep Caves Groundwater Investigation. Unpublished report for Water Authority of Western Australia. Perth.

Griffin, E.A., Hopkins, A.J.M., and Hnatiuk, R.J. (1983). Regional Variation in Mediterranean-type shrublands near Eneabba, south-western Australia. Vegetatio 52, 103-127.

Keighery. B. And Trudgen, M (1992). Remnant Vegetation on the Alluvial Soils of the Eastern Side of the Swan Coastal Plain. Unpublished report for Department of Conservation and Land Management, Australian Heritage Commission and Heritage Council of WA.

Panetta, F.D and Hopkins, A.J.M (1991). Weeds in Corridors: Invasion and Management. Pp 341-351 in Nature Conservation 2 the Role of Corridors ed by D.A. Saunders, and R.J Hobbs. Surrey Beatty & Sons Pty Limited, Chipping Norton, NSW.

Western Australian Planning Commission (1996). Central Coast Regional Strategy. A Strategy to Guide Land Use in the Next Decade. Perth.