Banksia Woodlands of the Swan Coastal Plain – Draft description and threats
For public consultation as part of the Threatened Species Scientific Committee’s threatened ecological community listing assessment under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).
Banksia Woodlands ecological community © Department of the Environment
1. DESCRIPTION OF THE ECOLOGICAL COMMUNITY 3
1.1 Name of the ecological community 3
1.2 Location and physical environment 3
1.3 Vegetation 4
1.3.1 Variability 5
1.3.2 Fungi 6
1.4 Fauna 9
1.5 Key diagnostic characteristics and condition thresholds 12
1.5.1 Key diagnostic characteristics 12
1.5.2 Condition thresholds 13
1.5.3 Further information to assist in determining the presence of the ecological community and significant impacts 13
1.6 National context and other existing protection 16
2. SUMMARY OF THREATS 17
3. SUMMARY OF ELIGIBILITY AGAINST LISTING CRITERIA 18
Appendix A – Species lists 19
Appendix B – Detailed description of threats 26
Land clearing and impacts associated with fragmentation 26
Climate change (increasing temps, declining rainfall, rainfall timing) 27
Groundwater drawdown 27
Altered fire regimes 28
Plant pathogens (causing dieback) 29
Invasive flora and fauna 30
Mining, exploration and extraction 30
Other disturbances to patches 31
Key threatening processes 31
1. DESCRIPTION OF THE ECOLOGICAL COMMUNITY
The ecological community is a woodland associated with the Swan Coastal Plain of southwest Western Australia. It typically has a prominent tree layer of Banksia with scattered eucalypts and other tree species present within or emerging above the Banksia canopy, and a species rich understorey including sclerophyllous shrubs, graminoids and forbs.
It is recommended that the ecological community be named Banksia Woodlands of the Swan Coastal Plain bioregion. The name appropriately describes the dominant canopy genus, structure1 and location that characterise the ecological community.
The national ecological community includes ecological communities recognised as threatened in Western Australia.
Throughout this document the full name of the ecological community may be abbreviated to ‘Banksia Woodlands’ or ‘the ecological community’.
1.2 Location and physical environment
The Banksia Woodlands ecological community is restricted to the Swan Coastal Plain IBRA bioregion2 and immediately adjacent areas, including the Dandaragan plateau, from Jurien Bay in the north, to Dunsborough in the south, and north/west on the Whicher and Darling escarpments (Banksia woodlands on these escarpments may be included in the ecological community definition, see 1.5.1 Key diagnostic characteristics). Sand plains occur further north in the Geraldton Sandplains bioregion, but support a significantly different structure and plant assemblage in a lower rainfall environment.
The Swan Coastal Plain bioregion consists of five main geomorphic entities that are roughly located parallel to the coastline (McArthur and Bettenay, 1974; McArthur, 2004). These geomorphic entities include the three coastal sand dune systems with ages increasing inland from the coast, the Quindalup System (Holocene; youngest and most westerly, fringing the current coastline), the Spearwood System (middle to late Pleistocene), and the Bassendean System (late Pliocene to early Pleistocene). Juxtaposed with these aeolian-formed dune systems, the Pinjarra Plain stretches out to the Ridge Hill Shelf and is composed of alluvial soils. The Ridge Hill Shelf is a narrow strip of land that forms the foothills of the Darling Scarp, and is composed of laterite covered spurs. Finally, the Dandaragan plateau is separated from the other major landform elements by the Gingin Scarp, an ancient shoreline formed by cretaceous marine sediments, and is composed of deep grey or pale brown sands with outcropping laterites (McArthur and Bettenay, 1974; McArthur, 2004).
The Swan Coastal Plain dune systems are generally composed of well-drained and weathered red/brown (Quindalup), pale yellow (Spearwood) or white (Bassendean) quartz sands, which form coarse-textured soils that are extremely poor in nutrients (McArthur and Bettenay, 1974; McArthur et al., 2004). The Quindalup and to a lesser extent Spearwood system, have a primary carbonate-rich origin, and limestone occurs in the profile and at the base of both dune systems. In contrast, the Bassendean dune system is characterized by deep siliciclastic sands that are not associated with underlying carbonate lithologies (McArthur and Bettenay, 1974; McArthur et al., 2004). The high content of shell fragments and carbonate material in the Quindalup System means that these sands are alkaline, typically in the pH range of 8 to 9. In contrast, Bassendean and Pinjarra soils are acidic, typically in the pH range of 5 to 6 (McArthur et al., 2004). Surrounding the lower interdunal swamps and lakes, the soils are poorly drained and rich in organic matter.
The Banksia Woodlands ecological community occurs on deep Bassendean and Spearwood sands, or occasionally on Quindalup sands (typically the eastern edge). The community occurs within an annual rainfall band of approximately 535 to 900 mm on deep sands and 650 to 750 mm on lateritic sands (Beard, 1990). Some areas, and some types of Banksia Woodlands are very sensitive to variations in groundwater (Groom et al., 2000; Froend and Drake, 2006).
There is a very strong seasonal variation in climate with long periods of summer drought (usually five to six months) coupled with high temperatures. Due to summer drought and vegetation flammability, these are fire prone habitats that include species with resilience to survive fires.