Shrublands and woodlands of the eastern Swan Coastal Plain

Advice to the Minister for the Environment and Heritage from the Endangered Species Scientific Subcommittee (ESSS) on a proposal to add an ecological community to Schedule 2 of the Endangered Species Protection Act 1992 (ESP Act)

Ecological community name

Shrublands and woodlands of the eastern Swan Coastal Plain.

Description

The community occurs mainly on the transitional soils of the Ridge Hill Shelf, on the Swan Coastal Plain adjacent to the Darling Scarp, but also extends marginally onto the alluvial clays deposited on the eastern fringe of the Swan Coastal Plain. The community reflects this transitional landform and soil zone between the Scarp and the Swan Coastal Plain, with many species present being more common on the Scarp and others more commonly associated with marri - wandoo woodlands on heavy soils. The community occurs as a shrubland, or a woodland of Banksia attenuata and Banksia menziesii, sometimes with Allocasuarina fraseriana, over diverse shrub and herb layers. It has been assessed by the WA Threatened Ecological Communities Advisory Committee as Critically Endangered.

Listed species in the ecological community

Caladenia huegelii.

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

None known.

Description of the community 'Shrublands and woodlands of the eastern Swan Coastal Plain' sufficient to distinguish it from any other ecological community

This community mainly occurs on soils mapped as the Forrestfield Unit of the Ridge Hill Shelf (Churchward and McArthur 1980). The most northerly occurrence is on the junction of this unit and the Guildford clays (Churchward and McArthur 1980). The Forrestfield unit is described by Churchward and McArthur (1980) as gently undulating spurs at the foot of the scarp, and is dominated by gravely and sandy soils. This area consists of coalescing alluvial fans at the bottom of the scarp and remnants of marine terraces (Ecologia Environmental Consultants 1991).

There are only two remaining occurrences of the community, one in an area known as Talbot Road bushland in Stratton (Occurrence 1), the other at Bushmead Rifle Range in Helena Valley (Occurrence 2). The occurrence in the Bushmead Rifle Range was located in the System 6 Update study (DEP 1996). Although statistical analysis of plot data indicates the two sites are the same community, there are some significant differences in structure and composition of the two sites (Gibson et al. 1994; DEP 1996). These differences may be due to natural variation in the community. Differences may also be partly attributed to compositional changes in Occurrence 2 as a consequence of grazing (Ecologia Environmental Consultants 1991).

Both of the known occurrences of this community occur mainly on sandy soils, and the site at Talbot Road bushland contains a variety of soil types from sandy silts (colluvium) to sand, according to Gozzard (1986). The structural units within this occurrence of the community vary from scrub to woodlands of Banksia attenuata over dense shrubs, possibly reflecting the variation in soils at this site. Species richness is high in the Occurrence at Talbot Road, with an average of 64 species occurring in plots of 100 m2 for the nine plots located in the community in reserve 23953 (Gibson et al. 1994).

Occurrence 2 at Bushmead Rifle Range consists of forest of Allocasuarina fraseriana and Banksia attenuata, with varying dominance of Allocasuarina. The understorey in Occurrence 2 is much less diverse than that in Occurrence 1 with 31 taxa recorded in the single plot in the occurrence (DEP 1996).

The community occurs as a shrubland, or a woodland of Banksia attenuata and Banksia menziesii, sometimes with Allocasuarina fraseriana, over a shrub layer that can include the species Adenanthos cygnorum, Hibbertia huegelii, Scaevola repens var. repens, Allocasuarina humilis, Bossiaea eriocarpa, Hibbertia hypericoides and Stirlingia latifolia. A suite of herbs including Conostylis aurea, Trachymene pilosa, Lomandra hermaphrodita, Burchardia umbellata and Patersonia occidentalis; and the sedges Mesomelaena pseudostygia and Lyginia barbata usually occur in the community. The weeds Gladiolus caryophyllaceus and Ursinia anthemoides are also common (Gibson et al. 1994; Department of Environmental Protection 1996)

Evidence that the description of the community 'Shrublands and woodlands of the eastern Swan Coastal Plain' is conventionally accepted

References and data that support the description and 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 (1994). Threatened or Poorly Reserved Plant Communities Requiring Interim Protection for the Swan Coastal Plain. Preliminary Maps. Environmental Protection Authority, Perth.

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

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 community 'Shrublands and woodlands of the eastern Swan Coastal Plain' is considered to be endangered within the meaning of Section 6 of the Act

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

1. The Forrestfield Unit to which this community type is virtually restricted has been extensively cleared for agriculture, mining, forestry, and urban development. Only 3.1 percent of the original 14,414 hectares of the unit remained uncleared in 1986 (Ecologia Environmental Consultants 1991)

2. Only about 79 hectares of the community remain. About 38 hectares is vested in the Commonwealth of Australia for the use and requirements of the Army, about 36 hectares is vested in the Shire of Swan and about five hectares is unvested.

3. Remaining patches are threatened by weed invasion, hydrological changes due to clearing and draining, too frequent fire and dieback resulting from infection by Phytophthora cinnamomi.

Past and current distributions of the community 'Shrublands and woodlands of the eastern Swan Coastal Plain'

The ecological community is located on the geomorphological unit adjacent to the Darling Scarp described by Churchward and McArthur (1980) as the Forrestfield unit of the Ridge Hill Shelf. The Forrestfield Unit consists of a one to three kilometre wide belt between the Darling and Gingin Scarps and the Darling Fault, from Walyunga National Park to Harvey (DEP 1996). The plant community is likely to have been always rare prior to extensive clearing of this geomorphological unit (Gibson et al. 1994). Only about 79 hectares of the community remain.

References that support information given in the nomination

Churchward, H.M. and McArthur (1980). Landforms and Soils of the Darling System. In: Atlas of Natural Resources, Darling System, Western Australia. Perth, Pinjarra and Collie Sheets. 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 Environment (1985). Conservation reserves for Western Australia; as recommended by the Environmental Protection Authority - 1983. The Darling System - System 6. Report 13, DCE, Perth.

Department of Conservation and Land Management (1988). Policy Statement No. 28 Reporting, Monitoring and Re-evaluation of Ecosystems and Ecosystem Management. Department of Conservation and Land Management, Perth.

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.

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.).

Keighery, B. (1996). Flora Information for Roadside Bush Protection Plans in the Shire of Serpentine - Jarrahdale. Report prepared for the Roadside Care Volunteers. Perth, Western Australia.

Keighery, B.J., Keighery, G.J., and Gibson, N. (1997). Floristics of Reserves and Bushland areas of the Perth Region (System 6) Parts XI - XV. Wildflower Society of Western Australia (Inc.), Nedlands.

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.

Keighery, G.J. and Keighery, B.J. (1993). Floristics of Reserves and Bushland Areas of the Perth Region (System 6). Parts V - IX. Wildflower Society of Western Australia (Inc.), Nedlands.