DRAFT Description, Threats Analysis and Priority Conservation Actions for
Plant communities on ferricrete/ironstone in south-west western australia
The Threatened Species Scientific Committee is assessing a nomination to list as a national ecological community a series of plant communities that occur on a restricted iron-rich substrate in southern Western Australia. The potential national ecological community has five regional component types, with significant variation in the species composition of each, and distances separating each type of between approximately 90 and 610km. The following document considers the combined entity encompassing the five regional types. Hereafter the term “ecological community” should be understood to stand for the potential national ecological community including those five regional type whose conformity as an entity with the definition of an ecological community under the EPBC Act 1999 and its conservation status is the subject of this document.
Part A DESCRIPTION AND THREATS ANALYSIS 1
1. Description 1
Name of the ecological community 1
Location and climate 1
Geology and landforms 2
Key diagnostic characteristics and condition thresholds 4
2. Surrounding environment and national context 7
3. Area critical to the survival of the ecological community 7
4. Geographic extent and distribution 7
5. Summary of threats 8
6. Other existing protection 9
7. Summary of eligibility for listing against EPBC Act criteria 10
Part B Priority Conservation Actions 12
1. Research priorities 12
2. Priority recovery and threat abatement actions 12
3. Existing plans/management prescriptions 13
Part C Appendices 15
Appendix A - Species lists 15
Appendix B - Detailed description of biology and ecological processes 17
Appendix C - Detailed description of national context 19
This ecological community is found in conjunction with the ferricrete floristic community regional type near Enabba. It is listed as an endangered Threatened Ecological Community by WA. The ecological community consists of raised areas of peat formed and fed by continuous discharge of groundwater (Rees and Broun, 2005). The peat provides a permanently moist environment which supports a diversity of invertebrate fauna (Rees and Broun, 2005). 20
Appendix D - Description of threats 21
Competition and land degradation by rabbits 23
Appendix E - Eligibility for listing against the EPBC Act criteria 24
Part D Bibliography 27
Part A DESCRIPTION AND THREATS ANALYSIS
Name of the ecological community
The name of the ecological community under assessment is Plant Communities on Ferricrete/Ironstone in South-West Western Australia. The name was suggested by the Western Australian Department of Environment and Conservation (DEC) as best describing the ecological community. Throughout this document it is referred to as the ecological community or the plant communities.
This ecological community was nominated for listing as threatened under theEPBC Act as part of a process to streamline the listing of state endemic ecological communities under federal and state processes.
Location and climate
The ecological community occurs as extremely restricted, disjunct patches within the Southwest Botanical Province of Western Australia (Meissner and English 2005a,b). Within this Province, there are restricted areas of ironstone and ferricrete soils which are associated with unique plant communities. These are currently known to occur in a number of areas in the south-west of Western Australia (WA) near Eneabba, at Gingin, at Busselton, the Scott River and near Albany. The known plant communities associated with each of these locations are referred to throughout this document as regional types, with patches within each type referred to as occurrences. The ecological community is found in the Swan Coastal Plain, Geraldton Sandplains, Jarrah Forrest and Warren IBRA bioregions (Interim Biogeographic Regionalisation of Australia version 6.1). The south-west of WA has a mild Mediterranean climate of warm, dry summers and cool, wet winters (Beard et al., 2000; Wheeler, 2002). Much of the area receives in excess of 1000mm per year (average of 800-1500mm), the majority of which falls between May and October (Wheeler, 2002).
Geology and landforms
The ecological community occurs as scattered patches on the coastal plain or on the footslopes of scarps and plateaux in south-west WA. On the coastal plain of WA, deep layers of iron-rich substrate are common, producing sumplands and damplands (Gibson et al., 2000). The soils associated with this geology are composed of deep layers of Quaternary sand deposits (Poot et al., 2008). However, the shallow soils associated with the ferricrete/ironstone substrate are extremely restricted in south-west WA and the plant communities associated with them are therefore also highly restricted (Gibson et al., 2000). The soils of the plant communities are generally very shallow, ranging from 0-20cm (Poot et al., 2008), with soil depth ranging throughout a patch of the ecological community. The soils are derived mainly from weathering of the underlying ironstone rock (Poot et al., 2008). The ferricrete/ironstone substrate can occur as a mosaic with other substrates, resulting in pockets or patches of deeper soil. Outcropping of ferricrete and ironstone rocks in the ecological community is common.
Around Gingin, Busselton, Scott River and Albany, the ecological community occurs on very shallow, reddish, loamy sands over massive ironstone rock (Poot et al., 2008). Ironstone soils contain more than 60% of ironstone gravel throughout the profile and have a distinct red-brown colour (CSIRO, 1983; Poot et al., 2008). Ironstone is thought to have formed in bogs, with iron being deposited by water percolating through the soil, followed by evaporation, to create a very hard stony habitat (Gibson et al., 2000). Around Eneabba, the ecological community occurs on very shallow red and brown loamy sands over ferricrete (Hamilton-Brown et al., 2004). Ferricrete is formed in the soil profile at the water table when iron oxides accumulate and cement together to form a gravely or nodule-rich band (Hamilton-Brown et al., 2004). The formation of the ferricrete/ironstone substrate is an ongoing process.
South-west WA receives an average of 800-1500mm of rain per year, most of which falls between May and October (Wheeler, 2002). The ironstone and ferricrete substrate on which the plant communities occur produces a specific hydrological regime. The shallow soil layer above the substrate impedes drainage, leading to inundation of the ecological community during heavy or prolonged rainfall (Meissner and English, 2005b). During the winter months, the plant communities experience numerous waterlogging and drainage events (Poot et al., 2008). The watertable is close to or above the surface for several months between May-October, drying out at the surface in summer (Smith and Ladd, 1994; Luu and English, 2004; Meissner and English, 2005a,b). The depth and length of inundation varies between occurrences, with some having very little or no standing water and others having obvious pools of water (Luu and English, 2004).
The plant communities are dependent on groundwater for formation and maintenance of the ferricrete or ironstone substrate (Hamilton-Brown et al., 2004). Groundwater generally comes close to or is above the surface during the winter months. Surface water which originates from rainfall during wetter months can also make its way down into the groundwater (Meissner and English, 2005b). As there are connections between the surface and groundwater through the ironstone or ferricrete, then both these sources affect the quantity and quality of water in the plant communities (Meissner and English, 2005b).
The occurrence of the plant community at Gingin is located on and connected to the Gnangara Mound, a shallow groundwater aquifer (Meissner and English, 2005b). Local hydrogeology is therefore likely to be very important in maintaining the community (Meissner and English, 2005b). The ferricrete plant communities around Eneabba are associated with organic mound springs which experience continuous discharge of groundwater in raised areas of peat (Rees and Broun, 2005). The groundwater which feeds these springs is related to the aquifer which forms and maintains the ferricrete (Hamilton-Brown et al., 2004). Water from these mound springs also flows into adjacent ferricrete plant communities adding to inundation in the wetter months. The southern ironstones near Busselton have also been identified as groundwater dependent ecosystems (Meissner and English, 2005a) and a suite of aquifers within sand or sandstone occur beneath the Scott River plant communities (Luu and English, 2004).
The ecological community is variable in terms of species composition and structure. This variation is found among regional types as well as among occurrences. Composition and structure also varies in response to disturbances such as fire and clearing. The plant communities are generally heathlands or shrublands with a proliferation of flowering annuals in the spring following winter inundation. Plants from the families Proteacae and Epacridacae make up the majority of woody vegetation. Low trees and/or shrubs can form a sparse to dense canopy, with grasses, herbs and smaller shrubs in the understorey. Annual herbs flower in the spring when the soil has dried out, and set seed in summer, generally dying out by autumn. The floral composition of a particular occurrence is thought to be a response to soil depth and degree of waterlogging (Smith and Ladd, 1994).
The Plant Communities on Ferricrete/Ironstone in South-West Western Australia ecological community is currently known to include the following WA ecological communities:
Shrublands and woodlands on Perth to Gingin ironstone (Perth to Gingin ironstone association) of the Swan Coastal Plain
This regional type consists of three occurrences within the Shire of Gingin, on heavy clay soils on the eastern side of the Swan Coastal Plain. It experiences shallow seasonal inundation with fresh surface water, and groundwater may come very close to or may reach the surface in wetter months (Meissner and English, 2005b). It is the only plant community on ironstone soils that is characterised by Rhodanthe spp. (massed everlastings) in the understorey (Meissner and English, 2005b). This everlasting-dominated herb layer does not occur on deeper soils adjoining the ironstone areas.
The vegetation is made up of a sparse shrubland over an herbaceous layer of annuals. Typical and common native species in the community are the shrubs: Kunzea aff. recurva, Grevillea curviloba subsp. incurva (narrow curved-leaf grevillea), Melaleuca viminea (mohan), Acacia saligna (golden wreath wattle), Jacksonia furcellata (grey stinkwood), Grevillea obtusifolia (Gingin gem) and Banksia sessilis (parrot bush); and the herbs: Rhodanthe manglesii (pink sunray), Tribonanthes australis and Isotropis cuneifolia subsp. glabra (granny bonnets).
The plant communities of this regional type are species-rich and are found on the southern Swan Coastal Plain bioregion near Busselton. Much of the high species diversity comes from annuals and geophytes (Phillimore et al., 2001). Many of the plant species in these communities are endemic to the region, and in some cases, to specific patches. Many of the plant species are susceptible to dieback disease and/or are obligate seeders.
The vegetation is sparse to dense shrubland over an herbaceous layer. Typical and common native species in the community are the shrubs: Kunzea aff. micrantha, Pericalymma ellipticum (swamp teatree), Hakea spp., Hemiandra pungens (snakebush) and Viminaria juncea (swish bush) and the herbs: Aphelia cyperoides, Centrolepis aristata (pointed centrolepis). The introduced species Hypochaeris glabra (smooth catsear) is also common in the community (Meissner and English, 2005a).
Ferricrete floristic community (Rocky Springs type)
The plant communities of this regional type are found on infrequently inundated red and brown sandy loams over ferricrete soils in the Eneabba region. Surrounding vegetation is generally sclerophyllous shrubland, or ‘kwongan’.
The vegetation of this regional type is a tall, generally dense shrubland. The occurrences are dominated by Acacia blakelyi (Blakely’s wattle), Allocasuarina campestris (tamma), Banksia strictifolia and Labichea lanceolata subsp lanceolata (Hamilton-Brown et al., 2004). Associated species include Alyogyne hakeifolia (Australian hibiscus), Borya sphaerocephala (pincushions), Isotoma hypocrateriformis (Woodbridge poison), Petrophile seminuda, Stylidium dichotomum (pins and needles), Thysanotus patersonii (twining fringe-lily) and Waitzia paniculata (woolly waitzia) (Hamilton-Brown et al., 2004).
Scott River ironstone association
The plant communities of this regional type are found on the Scott Coastal Plain near Augusta. The occurrences are highly variable in plant species composition, probably as a result of variation in soil type and depth (Luu and English, 2004).
The vegetation of this regional type is heathlands and shrublands, with dominant species depending on the degree of waterlogging (Luu and English, 2004). The occurrences are variously dominated by Melaleuca preissiana (moonah), Hakea tuberculata, Kunzea micrantha or Melaleuca incana subsp. Gingilup (grey honey-myrtle).The understorey is generally dominated by Loxocarya magna. All occurrences (except the long inundated wetlands and dense thickets) have a diverse annual flora of Stylidium spp. (trigger-plants), Centrolepis spp., Schoenus spp. (bog-rush) and Brizula spp. (Luu and English, 2004).
Wet ironstone heath community (Albany district)
This plant community is found north of Albany in the Porongurups (DEC, 2012b). It is located in a valley floor of the Twins Creek Conservation Reserve, adjacent to a stream (CALM, 2006).
The vegetation of this regional type is heath dominated by Kunzea recurva, K. preissiana, K. micrantha, Hakea lasiocarpha (long styled hakea), H. tuberculata, H. oldfieldii, H. cucullata (scallop hakea), H. sulcata (furrowed hakea), Petrophile squamata, Dryandra tenuifolia sp. tenuifolia, Adenanthos apiculatus, Melaleuca suberosa (cork bark honey myrtle), M. violacea (violet paperbark) and Gastrolobium spinosum (prickly poison). The understorey is made up of various moisture-loving species including sedges, Drosera spp. (sundew), mosses and several orchid species (CALM, 2006).
Key diagnostic characteristics and condition thresholds
The ecological community no longer exists at many sites where it was formerly present. In many cases, the loss is irreversible because sites have been permanently cleared or have undergone some other substantial modification that has removed their natural hydrological and biological characteristics. In other cases, the ecological community now exists in a disturbed or degraded state, and may be so degraded that it is impractical to restore it.
National listing focuses legal protection on the remaining occurrences of the ecological community that are functional, relatively natural and in relatively good condition. Condition thresholds help identify a patch of the threatened ecological community and when the EPBC Act is likely to apply to an ecological community. They 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 protection provisions of the EPBC Act would be focussed on the most valuable elements of Australia’s natural environment, while heavily degraded patches, which do not meet the condition thresholds, would be largely excluded from EPBC Act protection. The condition thresholds for the ecological community are based on those developed and used to assess condition by the WA Department of Environment and Conservation.
Although highly degraded patches would not be a part of 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. As such, these patches should not be excluded from recovery and other management actions (see also the Surrounding environmental and landscape context below).
Step 1 Key diagnostic characteristics
The key defining attributes for the ecological community are:
It occurs in the south-west botanical province of Western Australia (as per Beard et al., 2000);
Soils are shallow, loamy sands above a substrate of ironstone or ferricrete at or near the surface;
Rainfall is winter-dominated, mainly falling between May and October;
Sites are seasonally inundated in winter and may be waterlogged at this time;
Vegetation is generally shrubland or heathland with an open to closed structure;
A shrub or heath layer is present at all times, typically dominated by a combination of species from the genera: Acacia, Adenanthos, Allocasuarina, Banksia, Dryandra, Gastrolobium, Grevillia, Hakea, Hemiandra, Kunzea, Jacksonia, Labichea, Loxocarya, Melaleuca, Pericalymma, Petrophile and/or Viminaria; and
An annual herbaceous layer is present in the dry season (Oct-April).
Step 2 Condition thresholds
The listed ecological community is limited to patches that meet the description, key diagnostic characteristics and the following condition thresholds.
To be considered as part of the ecological community a patch should meet at least the Good Condition category of the DEC ecological community condition criteria (Government of Western Australia, 2000).
DEC assesses ecological community condition based on the following Vegetation Condition descriptions:
Pristine: Pristine or nearly so, no obvious signs of disturbance.
Very Good: Vegetation structure altered, with obvious signs of disturbance. For example, disturbance to vegetation structure caused by repeated fires, the presence of some more aggressive weeds, dieback, logging and/or grazing.
Good: Vegetation structure significantly altered by very obvious signs of multiple disturbance. Retains basic vegetation structure or the ability to regenerate it. For example, disturbance to vegetation structure caused by very frequent fires, the presence of some very aggressive weeds at high density, partial clearing, dieback and/or grazing.
Degraded: Basic vegetation structure severely impacted by disturbance. Scope for regeneration but not to a state approaching good condition without intensive management. For example, disturbance to vegetation structure caused by very frequent fires, the presence of very aggressive weeds, partial clearing, dieback and/or grazing.
Completely degraded: The structure of the vegetation is no longer intact and the area is completely or almost completely without native species. These areas are often described as “parkland cleared” with the flora comprising weed and crop species with isolated native trees or shrubs.
The following information should also be taken into consideration when applying condition thresholds.
A patch of the listed ecological community is defined as a discrete and continuous area of the ecological community, as described, and does not include substantial elements of other ecological communities. As the ecological community occurs in restricted locations that can be very small, no minimum patch size would be recommended. A patch of the listed ecological community may include small-scale disturbances, such as tracks or breaks, that do not alter its overall functionality, for instance the easy movement of wildlife or dispersal of plant propagules, and may also include small-scale variations in vegetation that are noted in the Description and National Context. In particular, there can be a mosaic of different soil types and depths within a patch that will produce differences in vegetation structure; however the whole patch should be considered part of the ecological community.
Buffer zones around the ecological community are important for protection against further weed invasions and disruptions to hydrology. To assist in the preservation of the patch and persistence of the ecological community, it is recommended that abuffer zoneof at least 50 m be maintained from the outer edge of the patch. However, the width of the buffer required may be greater, depending on the type of development proposed, the local hydrology, the vegetation in the buffer and other factors.
The sampling protocol involves developing a quick/simple map of the vegetation condition, landscape qualities and management history (where possible) of the site. The area with the most apparent native vegetation cover in the ground layer should be adequately sampled to determine estimates of ground cover.
Timing of surveys is an important consideration because the ecological community can be variable in its appearance between wet and dry seasons and between years depending on drought-rain cycles. Timing of surveys should also consider the detectability of mid and ground layer species at different times of their life cycle, or their recovery after recent disturbances (natural or human-induced) to the ecological community.