Habitat critical to survival includes the area of occupancy of known occurrences; similar habitat adjacent to important occurrences (i.e. within approximately 200m), i.e. poorly drained flats, depressions or winter wet flats with shallow sands and loams; remnant vegetation that surrounds or links several occurrences (this is to provide habitat for pollinators or to allow them to move between occurrences); and the local catchment for the surface, and potentially groundwater, that maintains the winter-wet habitat of the community. The plant assemblages are dependent on maintenance of the local hydrological conditions.
Occurrences that provide for representation of one of the clay pan communities across its geographic range and that can be managed for conservation and/or with conservation included in their purpose are considered critical to the survival of the clay pan communities and are therefore important occurrences. Occurrences within conservation reserves and Bush Forever sites (eg Brixton St wetlands occurrences 4, 35, 53-56; Forrestdale Nature Reserve occurrences 34, 51; Moore River Nature Reserve occurrence 22; Byrd Swamp occurrence 70; Drummond Nature Reserve occurrences 99, 100; Lake Wannamal Nature Reserve occurrences 102, 103, 106, 107; Wandoo National Park occurrence 111, Fish Road Nature Reserve occurrences 2, 76, and Tuart Forest eastern wetlands occurrences 113, 114); and occurrences with comparatively large intact areas of the community that are in relatively good condition outside of Bush Forever, are considered important occurrences (eg Austin Cove occurrences 26-29; Vasse-Yallingup rail reserve occurrence 74; Waroona occurrence 81).
12.1.5 International Obligations
This plan is fully consistent with the aims and recommendations of the Convention on Biological Diversity, ratified by Australia in June 1993, and will assist in implementing Australia’s responsibilities under that convention. This community is not listed under any specific international treaty, however, and therefore this IRP does not affect Australia’s obligations under any other international agreements.
1.6 Indigenous interests An Aboriginal Sites Register is kept by the Department of Aboriginal Affairs, and lists Artifact/Scatter and Ceremonial and Morphological sites in the vicinity of occurrences. The South West Aboriginal Land and Sea Council (SWALSC), an umbrella group, covers the areas considered in this plan. Appendix 1 identifies areas of the ecological community that contain sites that are known to have particular aboriginal significance. Actions identify the intention to continue liaison with relevant groups, including indigenous groups.
1.7 Social and economic impacts and benefits The implementation of this recovery plan has the potential to have some social and economic impact, where occurrences are located on lands not specifically managed for conservation, such as road reserves and private property. Recovery actions refer to continued liaison between stakeholders with regard to these areas. Negotiations will continue with land managers with respect to the future management of occurrences not in conservation estate.
Where specific active recreational pursuits such as four wheel driving and motorbike riding are prevented through access control, this may be perceived as a social impact, however, such access control also helps to prevent the continued degradation of the community and maintain other social benefits.
Occurrences may be threatened by proposals to clear for various developments or from hydrological change following clearing and development of adjacent land. Implementation of actions such as seeking to protect the hydrological processes in the areas adjacent to the community may result in a perceived impact on development.
13.1.8 Affected interests
Occurrences occur within the Shires of Armadale, Busselton, Carpel, Gosnells, Murray, Serpentine- Jarrahdale, Waroona, Gingin, Bunbury, Beverley, Capel, Dardanup, Kalamunda, Toodyay and Kojonup. They occur on land managed by local governments, administrators of railways, Public Transport Authority of Western Australia, Western Australian Planning Commission/ Department of Regional Development and Lands, Main Roads WA, Parks and Wildlife, Perth Airports Corporation, Conservation Commission, Water Corporation, University of WA, WA Planning Commission, and on private property.
14.1.9 Term of plan
The plan will operate from 2015 to 2020 but will remain in force until withdrawn or replaced. It is intended that, if the ecological communities are still ranked vulnerable or endangered in Western Australia after five years, the need for further recovery actions and the need for an updated recovery plan will be evaluated. The outcomes of the plan will be evaluated by the Midwest, Swan, Wheatbelt and South West region threatened flora and communities recovery teams.
15.1.10 Strategies for recovery
To identify, and influence the management of the areas in which the community occurs, so maintaining natural biological and non-biological attributes of the sites and the current area covered by the community.
To conduct appropriate research into the ecological characteristics of the community to develop further understanding about the management actions required to maintain or improve its condition.
Clearing The seasonal clay-based wetland communities of the south west are amongst the most threatened assemblages in Western Australia. It is estimated that >90% of the original extent of these wetlands has been cleared for agricultural use (Gibson et al. 2005). Clay pans in the Perth area have also historically been cleared and quarried for clay for use in manufacturing bricks and tiles.
Hydrological changes Altered hydrology due to anthropogenic causes, in urbanised areas in particular, is likely to be an increasing threat to the clay pans. Drainage to lower watertables, clearing resulting in a decline in evapotranspiration and increased surface runoff, and water quality declines are likely to increasingly impact the hydrologic regimes of the clay pan communities. Altered periods of ponding may affect the timing of growth of herbs in the understorey, and may also affect the species composition of the community by favoring different taxa. Any changes to the natural hydrology of the clay pans can affect composition as they are dependent on the timing of filling and drying at appropriate times of the year.
Increased nutrient levels in surface water in occurrences adjacent to areas such as farm lands and residential areas is likely to favour weeds as weeds are adapted to higher nutrient levels than native flora.
Hydrological changes such as increased depth or period of inundation may cause salt accumulation near the surface. This has been noted in areas of the southern Swan Coastal Plain since around the 1950s as a result of clearing (Smith and Ladd 1994). Due to the widespread clearance of native perennial vegetation and its replacement with urban areas and farmlands, rising groundwater in the surrounding region may result in increased surface water into clay-based wetlands (Gibson et al. 2005). Salinity risk mapping indicates that many clay pans are in susceptible areas (National Land and Water Resources Audit 2001).
Salinisation may increase as a result of evaporation of surface water. If increased ponding occurs in the community due to urbanisation or clearing in the catchment, evaporation of a greater volume of water may result in larger amounts of residual salt. This is especially true for clay soils, which inhibit rainfall infiltration and result in high evaporation rates and concentration of salts (Davidson 1995).
Salinisation and increased nutrients have been observed at a clay pan in Drummond Nature Reserve (Chow et al., 2010). There is currently no hydrological connection between the surface water in the clay pan and groundwater at this site, however evidence suggests increased volumes of nutrient enriched water in the clay pan as a result of regional clearing.
In some other areas groundwater is very close to the surface. At clay pans in Brixton Street, groundwater is 0–3 metres below the surface at the end of spring (Davidson, 1995). Surface waters may link to groundwater in winter and may influence the quantity and quality of water on the surface of the sites.
The levels of salinity in the community will need to be monitored to determine if salinisation poses a major threat to the communities, and the sources determined.
Weed invasion Weeds change the natural diversity and balance of ecological communities and are a major threat to the clay pans. About 16% of the flora for the clay pans are weeds (Gibson et al., 2005) and some are particularly aggressive.
Weeds displace native plants, particularly following disturbances such as too frequent fire, grazing or partial clearing, and compete with them for light, nutrients and water. They can also prevent recruitment, cause changes to soil nutrients, and affect abundance of native fauna. They can also impact on other conservation values by harbouring pests and diseases, and increasing the fire risk.
Introduced South African bulbous plants are a particularly serious group of weeds in clay pans. As the taxa occur in similar habitat in South Africa, many have the ability to invade relatively undisturbed clay pan habitat and displace the rich herbaceous flora. Watsonia meriana, Sparaxis bulbifera (harlequin flower), Moraea flaccida (one leafed cape tulip), Hesperantha falcata and Freesia alba x leichtlinii (freesia) are of particular concern. Seed and cormels are spread into undisturbed areas in sheet waterflow across wetlands (Brown and Brooks 2003b, Brown et. al., 2008). South African perennial grasses are another serious group of weeds that also occur in similar habitat in South Africa and have the ability to invade clay pans in good condition following disturbance events such as fire. Tribolium uniolae (haas grass), Eragrostis curvula (lovegrass) and Hyparrhenia hirta (tambookie grass) are of particular concern and are a priority for control. The impacts of annual weeds are less well known but many move into intact vegetation following a disturbance event and appear to displace the native annual flora. These include Isolepis hystrix, Parentucellia viscosa (bartsia)andHypochaeris glabra (flat weed) (see also Appendix 2).
Sources of weed invasion include adjoining areas of urban and agricultural use, drains, and tracks within and near the clay pans. All these sources increase vulnerability to weed invasion following any type of disturbance. The clay pans appear reasonably resistant to weed invasions due to seasonal inundation and hardness of soils in the summer and changes to these elements may alter their ability to resist weed invasion (Keighery 1996).
Grazing Grazing of native vegetation causes alterations to species composition through selective removal of edible species, the introduction and enhancement of weeds by the addition of dung, and through trampling and general disturbance. The presence of feral animals such as rabbits (Oryctolagus cuniculus) and pigs (Sus scrofa) is a concern as they disturb the vegetation by grazing and burrowing.
Occurrences at Fish Road (Occurrence 2, 76), Forrestdale Lake (Occurrences 33, 34, 46, 47, 80, 86), Nicholson Road (Occurrences 43, 44, 82), Karnup Road (Occurrence 45), Plantation Road (Occurrence 87), Keane Road (Occurrences 88 and 89), Brixton St (rabbits, occurrences 35, 50, 53), Ellen Brook (rabbits are fenced in, foxes are fenced out, occurrence 31), Bullsbrook (occurrence 8), Austin Bay (occurrence 12) have all been threatened by grazing to some degree, namely by rabbits, horses and kangaroos. The significance of the impact, however, has not been quantified through monitoring. Pigs have been recorded at Goonaping, and Moore River and Drummond Nature Reserves (occurrences 22, 111, 99 and 100).
Altered fire regimes Inappropriate fire regimes are a significant threat to the clay pan communities. Historically, fire within the clay pans was probably only very occasional. It is likely that some of the clay pan types such as the Shrublands on dry clay flats may be adapted to occasional fire as they contain species that will easily carry fire when vegetation is dry, and some component shrubs would reproduce from seed following fire. The fire response of the major types of clay pan vegetation needs to be determined however.
The risk of fire is generally increased by the presence of urban areas nearby. In addition, grassy weeds in the understorey are often more flammable than many of the original native species in the herb layer. Many of the occurrences have been burnt recently, including the occurrences on Fish Road (Occurrence 2, 76) and Nicholson Road (Occurrences 43, 44, 82). The fire responses of the typical and common vascular plants in the clay pan types (from Gibson et al. 1994) occur in Appendices 2 and 3.
Anecdotal evidence indicates that fire may exacerbate the impact of drying climate in clay pan communities. For example, following fire in Ambergate reserve (encompasses occurrence 21) community structure altered and reduced rainfall is believed to be a contributing factor. Shrub species such as Pericalymma ellipticum and Verticordia plumosa var. ananeotes have not recovered well post-fire and there has been a notable increase in sedge cover (1B. Lullfitz personal communication).
Disease Soil types have a clear correlation with the occurrence of dieback disease caused by the water moulds Phytophthora species around the Perth metropolitan area. Davison and Tay (1986) state ‘Increased sporulation and growth of P. cinnamomi will not occur in waterlogged soil because aeration is inadequate’. The clay pan communities occur on heavier soils that are thus probably a less susceptible habitat, resulting in a reduced susceptibility of the communities to the disease, although the disease has been recorded at Bullsbrook Nature Reserve (contains occurrence 8). In order for the disease to take hold within the occurrences a combination of factors such as temperature and rainfall need to be optimal for the spread of dieback. Regardless the risk of disease introduction should be minimized by ensuring good hygiene procedures. This includes adequately washing down any equipment used on or adjacent to the community and restricting access by vehicles and machinery to dry soil conditions.
Phytophthora dieback disease particularly affects Proteaceae and Myrtaceae families that are floristically and structurally dominant in some areas of the clay pan communities.
Plant species growth form may influence susceptibility to Phytophthoradieback disease, with the herbaceous perennials, annuals and geophytes that are common in these clay pans being apparently unaffected. Woody perennials are generally found to be the most susceptible. Monocotyledons generally have low susceptibility to the disease, as their density increases in sites with historical infections as compared with healthy uninfected areas. As the clay pan communities generally have a high proportion of their diversity associated with the annual herb and sedge layers, these particular communities may be less affected than other sites that are dominated by other structural formations such as woodlands and forests.
The disease Myrtle Rust (Puccinia psidii sens. lat) also has potential to impact the clay pans if it becomes established in Western Australia, as it may affect some of the dominant myrtaceous shrubs in the community (Australian Network for Plant Conservation 2012).
Loss of overstorey including taller shrubs caused by either Phytophthora species or Myrtle Rust may lead to a change in the herb layers as a result of increased sun penetration and decreased shading.
Disturbance from recreational activities Inappropriate recreational uses such as four wheel drive vehicles and dirt bikes pose a risk to the clay pan communities. Rubbish dumping also occurs in clay pans that are close to urban areas such as Brixton St Wetlands. These activities cause direct damage to vegetation, and can lead to weed, or disease introductions such as Phytophthora species.
Drying climate The clay pans are at risk from a drying climate with effects such as reduced surface water due to significantly less rainfall. As winter rainfall declines over the Swan Coastal Plain there may be a significant impact to the clay pans and component species that are dependent on particular water regimes. The drying trend in the south-west of Australia is forecast to significantly worsen (Western Australia Climate Science Centre, 2010). It is noted, however, that a drying climate as a threatening process is outside the scope of this recovery plan.
Any on-ground works (significant clearing, burns, proposals with potential to alter drainage or water quality) within or in the immediate vicinity of the clay pans should be assessed. Proponents should demonstrate that on-ground works will not have a significant impact on the clay pan communities, or on their habitat or potential habitat. This includes avoiding or mitigating:
land clearing leading to loss of locations defined as ‘core areas’ of the clay pans
clearing leading to significant increase in fragmentation of the communities
a significant increase in opportunity for introduction or increase in density of weeds or
introduced /feral animals known to damage the communities
proposals that will result in a significant increase in fire frequency
proposals that will modify the hydrological regime of the clay pans.