Castlereagh Scribbly Gum and Agnes Banks Woodlands of the Sydney Basin Bioregion: DRAFT DESCRIPTION
1. DESCRIPTION OF THE ECOLOGICAL COMMUNITY
The Castlereagh Scribbly Gum and Agnes Banks Woodlands of the Sydney Basin Bioregion (hereafter referred to as Castlereagh Scribbly Gum and Agnes Banks Woodlands or the ecological community) includes a range of vegetation and fauna associated with sand or gravel soils of the Hawkesbury-Nepean river system in western Sydney. Vegetation consists of low woodlands with sclerophyllous shrubs and a patchy ground layer of graminoids and forbs.
1.1 Name of the ecological community
The name of the ecological is Castlereagh Scribbly Gum and Agnes Banks Woodlands of the Sydney Basin Bioregion. The ecological community was nominated and placed on the 2009 Finalised Priority Assessment List as part of a broader ecological community, named the Hinterland Sand Flats Forest and Woodland of the Sydney Basin Bioregion. Following consultation with experts during the assessment process it was determined that an ecologically distinct assemblage is difficult to identify from the eight smaller vegetation units that were proposed to be combined into the broader ecological community.
The definition of the ecological community has been narrowed to incorporate two vegetation units with similar floristics that are typically co-located in the Hawkesbury-Nepean region west of Sydney on sandy substrates.
The name of the ecological community reflects its structure and location and combines the names of the two vegetation units. The two vegetation units also correspond with two threatened ecological communities listed separately under the New South Wales (NSW) Threatened Species Conservation Act 1995 (TSC Act). Information regarding the NSW listed ecological communities can be found at: http://www.environment.nsw.gov.au/determinations/castlereaghscribblygumFD.htm and http://www.environment.nsw.gov.au/determinations/AgnesBanksWoodlandSydneyEndComListing.htm
1.2 Location and physical environment
The Castlereagh Scribbly Gum and Agnes Banks Woodlands ecological community is located in the Sydney Basin Bioregion as defined by version 7 of the Interim Biogeographic Regionalisation of Australia (IBRA v 7).
It occurs almost exclusively on the Cumberland Plain, in the Castlereagh area in the north-west, and smaller occurrences near Holsworthy (some patches at Holsworthy are just outside the Cumberland Plain), Kemps Creek and Longneck Lagoon (Tozer et al., 2010; NSW Scientific Committee, 2013).
The ecological community occurs primarily on Tertiary sands and gravels of the Hawkesbury-Nepean river system. These ancient alluvial soils were deposited by the rivers in sites that can be quite distant from the present-day flood zones (James, 1997; Keith, 2004). At Agnes Banks it primarily occurs on Aeolian (wind-blown) sands overlying Tertiary alluvium.
The soils of the ecological community are typically low in nutrients, unlike more recent alluvial deposits (Keith, 2004). The sediments on which the ecological community occurs may be almost pure sand. The sand deposits often transition to, and include, areas of gravel and clay.
Altitude and Climate
The ecological community occurs at low elevations up to 70 m above sea level (ASL) (Tozer et al., 2010).
The ecological community is found on flat or gently undulating terrain on the valley floor in rain shadow areas typically receiving 700-900 mm annual rainfall (Keith, 2004).
The low altitude and hinterland position within the Cumberland Plain provide the ecological community with a warmer and drier climate than surrounding landscapes on escarpments.
The Castlereagh Scribbly Gum and Agnes Banks Woodlands range from woodland to low open-woodland with the canopy species typically 10-15 m tall (Benson, 1981; Keith, 2004).
The ecological community’s understorey has a prominent and diverse layer of sclerophyll shrubs. It typically has a patchy ground cover of sedges and grasses. However, in areas of poorly drained soil there may be less species diversity in the mid layer and the ground layer may contain a high diversity of sedges and grasses (Benson, 1981; Tozer et al., 2010).
The isolation of the alluvial deposits in the Hawkesbury-Nepean river valley and differences in the soil characteristics have led to the development of differences in species composition and abundance across the range of the ecological community (Keith, 2004). For example, this is expressed in differing abundance of Melaleuca and Banksia species. In addition, the Agnes Banks vegetation occurs on Aeolian sand and can contain a number of species reminiscent of communities closer to the coast, such as Dillwynia glaberrima, Ricinocarpos pinifolius (wedding bush) and Banksia aemula (wallum).
The canopy contains, and is often dominated by, one or more of the following species: Angophora bakeri (narrow leaved apple), Eucalyptus racemosa(narrow-leaved scribbly gum) and E. parramattensis subsp. parramattensis (Parramatta red gum) (Keith, 2004; Tozer et al., 2010).Melaleuca species including M. decora (paperbark) may also be prominent in the canopy (and/or mid layer) of the ecological community. Eucalyptus fibrosa (red ironbark) is also occasionally present in the canopy (Keith, 2004; Tozer et al., 2010).
Mid layer (shrubs)
A shrub layer up to 2 m tall is present in well drained areas. Characteristic mid layer species include: Banksia aemula (wallum), B. serrata (old man banksia), B. oblongifolia (fern-leaved banksia), B. spinulosa (hairpin banksia), Melaleuca decora (paperbark), Conospermum taxifolium (variable smoke bush), Leptospermum trinervium (flaky-barked tea-tree), Dillwynia sericea (showy parrot-pea), Monotoca scoparia (broom heath), Platysace ericoides, Persoonia nutans (nodding geebung), Pimelea linifolia (slender rice-flower) and Hakea sericea (silky hakea).
Ground layer (graminoids and forbs)
The ground layer consists of a diverse range of graminoids and forbs including Themeda triandra (kangaroo grass), Entolasia stricta (wiry panic), Cyathochaeta diandra, Dianella revoluta subsp. revoluta (blue flax-lily), Lepidosperma urophorum (at Agnes Banks), Stylidium graminifolium (grass triggerplant), Lepyrodia scariosa, Mitrasacme polymorpha, Trachymene incisa subsp. incisa, Laxmannia gracilis (slender wire lily), Lomandra spp.and Aristida warburgii (Keith, 2004; Tozer et al., 2010; NSW Scientific Committee, 2011a, 2011b).
Common fauna that use the ecological community for food or shelter include Ctenotus taeniolatus (striped skink), Tiliqua scincoides (eastern blue-tongued lizard), Petaurus breviceps (sugar glider), Myotis macropus(southern myotis) and Trichosurus vulpecula (common brushtail possum). Frogs such as Litoria verreauxii (Verreaux's tree frog), Crinia signifera (common eastern froglet) and Limnodynastes tasmaniensis (spotted marsh frog) use areas of inundation in the ecological community for breeding (Jones et al., 1997).
The avifauna is predominantly composed of small to medium sized insectivorous birds. Typical birds include Smicrornis brevirostris (weebill), Acanthiza reguloides and A. nana (buff-rumped and yellow thornbills), Petrochelidon nigricans (tree martin), Artamus cyanopterus (dusky woodswallow), Colluricincla harmonica (grey shrike-thrush), Pachycephala rufiventrisand P. pectoralis (rufous and golden whistler), Daphoenositta chrysoptera (varied sittella), Melanodryas cucullata (hooded robin), Pardalotus striatusand P. punctatus(striated and spotted pardalote) and Lichenostomus fuscus (fuscous honeyeater) (Jones et al., 1997). The locally rare Petroica goodenovii (red-capped robin) is mostly found in the ecological community. Tyto alba (barn owl) occurs in disturbed areas of the ecological community. They feed on introduced Musmusculus (house mice), reptiles and insects (Jones et al., 1997). There have also been sightings of the locally rare Entomyzon cyanotis (blue-faced honeyeater) in remnants of the ecological community in the Castlereagh area (NSW National Parks and Wildlife Service, 1997).
Some areas of the ecological community (for example, at Agnes Banks) are similar to coastal heaths and this is reflected in the assemblage of bird species in these areas, which contain elements of the sandstone bird communities. Phylidonyris niger (white-cheeked honeyeater), Hylacola pyrrhopygia (chestnut-rumped heathwren), Malurus lamberti (variegated fairy-wren), Calyptorhynchus funereus (yellow-tailed black cockatoo) occur in this part of the ecological community (Jones et al., 1997).
Although a number of migratory birds use the ecological community, most migratory birds arrive in spring and depart in autumn. However, importantly, the threatened Lathamus discolor (swift parrot) and rufous whistler are winter migrants (Jones et al., 1997).
1.5 Key diagnostic characteristics and condition thresholds
National listing focuses legal protection on remaining patches of the ecological community that are most functional, relatively natural (as described by the ‘Description’) and in relatively good condition. Key diagnostic characteristics and condition thresholds assist in identifying a patch of the threatened ecological community, determine when the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) is likely to apply to the ecological community and to distinguish between patches of different quality. The ecological community may exhibit various degrees of disturbance and degradation. This degree of degradation has been taken into account in developing the condition thresholds.
1.5.1 Key diagnostic characteristics
The key diagnostic characteristics presented here summarise the main features of the ecological community. These are intended to aid the identification of the ecological community, noting that a broader description is given in the other sections. Key diagnostic characteristics for describing the Castlereagh Scribbly Gum and Agnes Banks Woodlands ecological community are that it:
Is solely distributed within the Sydney Basin Bioregion.
Occurs on flat or gently undulating terrain on valley floors.
Occurs at low altitude up to 70 m ASL
Occurs on sandy soil, on deposits of tertiary alluvium which are sometimes overlayed with Aeolian deposits (i.e. parts of the Agnes Banks occurrences). The sand deposits often transition to and include areas of gravel and clay.
The vegetation structure is typically low woodland, less than 15 m tall with a prominent shrub layer.
The canopy contains, and is often dominated by one or more of the following species: Angophora bakeri, Eucalyptus racemosa and E. parramattensis subsp. parramattensis.
1.5.2 Condition thresholds
Condition classes and thresholds provide guidance for when a patch of a threatened ecological community retains sufficient conservation values to be considered as a Matter of National Environmental Significance, as defined under the EPBC Act. This means that the referral, assessment and compliance provisions of the EPBC Act are focussed on the most valuable elements of the ecological community. Very degraded patches that do not meet the condition thresholds will be largely excluded from national protection.
Although very degraded/modified patches are not protected as the ecological community listed under the EPBC Act, it is recognised that patches that do not meet the condition thresholds may still retain important natural values and may be protected through State and local laws or schemes. Therefore, these patches should not be excluded from recovery and other management actions. Suitable recovery and management actions may improve these patches to the point that they may be regarded as part of the ecological community fully protected under the EPBC Act. Management actions should, where feasible, also aim to restore patches to meet the high quality condition thresholds outlined below.
< Note: exact vegetative cover, patch size and tree diameter at breast height (dbh) figures are to be finalised through further data analysis and consultation.>
For Castlereagh Scribbly Gum and Agnes Banks Woodlands, categories A and B are considered moderate quality condition and the minimum thresholds for a patch of the ecological community to be subject to the referral, assessment and compliance provisions of the EPBC Act. Categories C and D are considered the minimum thresholds for a patch of Castlereagh Scribbly Gum and Agnes Banks Woodlands to be regarded as an example of high quality condition.
Category and Rationale
A. Moderate condition class
Represented by medium to large-size patch as part of a larger native vegetation remnant and/or with mature trees
Patch size >0.5ha
>30% of the perennial understorey vegetation cover is made up of native species
The patch is contiguous with a native vegetation remnant (any native vegetation where cover in each layer present is dominated by native species) >1ha in area
The patch has at least one tree with hollows or at least one large locally indigenous tree (>80cm dbh). Where patches are >1ha, a density of at least one mature tree/tree with hollows per hectare is required.
B. Moderate condition class
Represented by medium to large size patch with high quality native understorey
Patch size >0.5ha
>50% of the perennial understorey vegetation cover is made up of native species.
C. High condition class
Represented by medium to large size patch with very high quality native understorey
Patch size >0.5ha
>70% of the perennial understorey vegetation cover is made up of native species.
>50% of the perennial understorey vegetation cover is made up of native species.
Perennial understorey vegetation cover includes vascular plant species of the ground and shrub layers with a lifecycle of more than two growing seasons. Measurements of perennial understorey vegetation cover exclude annuals, cryptogams, leaf litter or exposed soil.
Contiguous means the patch of the ecological community is continuous with, or in close proximity (within 100 m), of another patch of vegetation that is dominated by native species in each vegetation layer present.
1.6 Defining a patch
The ecological community is characterised by the presence of a low eucalypt canopy, (sometimes interspersed with Melaleuca or Banksia species), a prominent and diverse shrub layer and a typically patchy ground layer of graminoids and forbs. At its boundary the ecological community may grade into a range of other woodland types and vegetation communities, such as Castlereagh Swamp Woodland and Castlereagh Ironbark Forest (see Section 1.10 for more information on intergrading communities).
A patch is defined as a discrete and continuous or semi-continuous area of the ecological community. A patch may include small-scale disturbances, such as tracks or breaks, watercourses or small-scale variations in vegetation that do not significantly alter its overall functionality (functionality here refers to processes such as the movement of wildlife and pollinators, the dispersal of plant propagules, activities of seed and plant predators and many others).
1.7 Area critical to the survival of the ecological community
Areas that meet the condition thresholds are considered critical to the survival of Castlereagh Scribbly Gum and Agnes Banks Woodlands. Additional areas, such as adjoining native vegetation and areas that meet the description of the ecological community but not the condition thresholds are also considered important to the survival of the ecological community. It is also important to consider the surrounding environment and landscape context.
1.8 Geographic extent and patch-size distribution
Since European settlement, the ecological community has undergone a reduction in extent of approximately 60% (Table 1).
Table 1. Estimates of decline and extent of the ecological community.
Castlereagh Scribbly Gum Woodland (Tozer et al., 2010)
Average patch size is approximately 23 ha (based on SCIVI data from Tozer et al., 2006). The average patch size calculation excludes patches under 0.5 ha – these account for 65 % of mapped patches and occupy a total of 24 ha.
1.9 Relationships to State-listed ecological communities
NSW Threatened Species Conservation Act 1995:
Castlereagh Scribbly Gum Woodland in the Sydney Basin Bioregion – vulnerable
Agnes Banks Woodland in the Sydney Basin Bioregion – endangered.
The state listed ecological communities do not include condition thresholds.
The ecological community corresponds, entirely or in part, to the following vegetation classifications:
Benson (1992) and James (1997)
14a Castlereagh Scribbly Gum Woodland
14b Agnes Banks Woodland
Tozer et al. (2010)
DSF p7 Castlereagh Scribbly Gum Woodland
DSF p239 Agnes Banks Woodland
VIS Vegetation Classification
883 Hard-leaved Scribbly Gum - Parramatta Red Gum Heathy Woodland of the Cumberland Plain, Sydney basin Bioregion
958 Narrow-leaved Apple - Hard-leaved Scribbly Gum Heathy Woodland on Sand at Agnes Banks, Sydney Basin Bioregion.
1.10 Differences to similar or intergrading ecological communities
The following vegetation types occur on sand deposits in the Sydney Basin Bioregion. Their sandy substrate gives them some similarities with Castlereagh Scribbly Gum and Agnes Banks Woodlands. However, most occur outside the Cumberland Plain and at higher altitudes, resulting in a range of differences in their attributes (including floristic composition and structure).
1.10.1 Similar communities
Mellong Woodland (10me) (Ryan et al., 1996)
The Mellong Plateau has younger, Quaternary alluvial deposits of deeply leached sands at a higher elevation (340 m ASL). The proximity of this vegetation type to surrounding sandstone vegetation is reflected in its similarity to sandstone ridge-top flora of the Sydney Basin found at higher elevations.
Thirlmere Lakes Swamp Woodland
Thirlmere Lakes Swamp Woodland occurs on laterised Cretaceous sandy alluvium and has a tree layer of Eucalyptus parramattensis (drooping red gum) and Melaleuca linariifolia (flax-leaved paperbark), shrubs of Acacia longifolia (Sydney golden wattle), Melaleuca thymifolia (thyme honey myrtle) and a ground layer of Lepyrodia muelleri.It does not contain Eucalyptus racemosa (narrow-leaved scribbly gum).
Kurri Sand Swamp Woodland is a similar vegetation type that occurs outside the Cumberland Plain in the Hunter Valley. This vegetation type also occurs on sand but lacks the characteristic Eucalyptus racemosa (narrow-leaved scribbly gum) and contains a different subspecies of E. parramattensis (subsp. decadens).
Warkworth Sands Woodland
On sand deposits at Warkworth in the Hunter Valley, the vegetation has a canopy dominated by Angophora floribunda (rough-barked apple), Eucalyptus tereticornis (forest red gum), Acacia filicifolia (fern-leaved wattle), Banksia integrifolia subsp. integrifolia (coastal banksia) and Pteridium esculentum (common bracken). The occurrence of Callitris endlicheri (black cypress pine) and Exocarpos cupressiformis (native cherry), Brachychiton populneus subsp. populneus (kurrajong), Allocasuarina luehmannii (bull oak) and the lack of key canopy species make it distinct from Castlereagh Scribbly Gum and Agnes Banks Woodlands.
Elderslie Banksia Scrub Forest
This low woodland is listed under the NSW TSC Act as endangered. Although it occurs on sand deposits within the Cumberland Plain, it is differentiated from Castlereagh Scribbly Gum and Agnes Banks Woodlands by its species composition, including its characteristic canopy species Banksia integrifolia and Eucalyptus botryoides.
1.10.2 Intergrading communities
Cooks River - Castlereagh Ironbark
The sand deposits where the ecological community occurs are usually adjacent to gravel-clay soils. These soils support ironbark vegetation communities such as Cooks River - Castlereagh Ironbark (NSW Scientific Committee, 2011c). Occasional ironbark trees also occur in the Castlereagh Scribbly Gum and Agnes Banks Woodlands ecological community.
Castlereagh Swamp Woodland
The ecological community is also adjacent and may intergrade with Castlereagh Swamp Woodland (a listed community under the NSW Threatened Species Conservation Act 1995), which occurs on poorly draining clay soils. Castlereagh Swamp Woodland shares some similarities in vegetation, however the canopy is characterised by Melaleuca decora and Eucalyptus parramattensis subsp. parramattensis.
Cumberland Plain Shale Woodlands and Shale-Gravel Transition Forest
Shale-Gravel Transition Forest (9d) (Benson, 1992; James, 1997) (part of the nationally listed Cumberland Plain Shale Woodlands and Shale-Gravel Transition Forest) forms a transition between Castlereagh Scribbly Gum and Agnes Banks Woodlands and Cumberland Plain Woodland. Several species are good indicators of transitional forest, such as Eucalyptus moluccana (grey box), E. fibrosa (red ironbark), E. eugenioides (thin-leaved stringybark), E. racemosa (narrow-leaved scribbly gum), Angophora floribunda (rough-barked apple), E. longifolia (woollybutt), Melaleuca nodosa (prickly-leaved paperbark), Dillwynia tenuifolia, Grevillea juniperina and Cryptandra spinescens (James, 1997).
Castlereagh Shale-Gravel Transition Forest
Castlereagh Shale-Gravel Transition Forest (listed as endangered in NSW) occurs on clays derived from tertiary alluvium on the Cumberland Plain and has a canopy dominated by Eucalyptus fibrosa (red ironbark) and Melaleuca decora (paperbark). This vegetation type can be found in some of the same conservation reserves as Castlereagh Scribbly Gum and Agnes Banks Woodlands, for example Windsor Downs Nature Reserve, with transitional areas likely to contain a rich mixture of species typical of both shale and tertiary alluvium.
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NSW Scientific Committee (2011c). Cooks River/Castlereagh ironbark forest in the Sydney Basin Bioregion - endangered ecological community listing. Available on the internet at: http://www.environment.nsw.gov.au/determinations/CooksRiverCastlereaghIronbarkForestSydneyEndComListing.htm
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