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Interim recovery plan no. 198 Assemblages of Organic Mound (Tumulus) Springs of the Swan Coastal Plain Recovery Plan


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Evaluation of the plan’s performance: The Department of Environment and Conservation will evaluate the performance of this recovery plan in conjunction with the Recovery Team. In addition to annual reporting on progress with listed actions and comparison against the criteria for success and failure, the plan is to be reviewed within five years of its implementation.



Recovery plan objective(s): To maintain or improve the overall condition of the tumulus springs and the associated fauna and plant community in the known locations and reduce the level of threat, with the aim of reclassifying the community from Critically Endangered to Endangered.
Criteria for success:

An increase of 10% or more in the area, and/or increase in the number of occurrences of this community under conservation management.


Maintenance in terms of diversity and basic composition of native invertebrate species (as described in Ahmat 1993; Jasinska and Knott 1994; Pinder 2002) taking account of natural change in the community over time. This will be measured as a loss of no more than 10% of the native invertebrate species in any one spring over the life of the plan.
Improvement in the condition of the habitat, in terms of re-establishment of fringing buffer vegetation, reduction of numbers of exotic species and of other threatening processes as defined in this document. This will be measured as follows:

  • a gain in the area of buffer vegetation under conservation management adjacent to the springs of 10% or more,

  • reduction of 10% or more in the cover of exotic plant taxa in the springs or buffer areas,

  • groundwater levels and quality maintained within the parameters expected as a consequence of natural change, by comparison with monitoring results for the Gnangara Mound in areas remote from development.



Criteria for failure:


A decrease of 10% or more in the area covered by the springs, and/or decline in the number of occurrences of this community under conservation management.
A decline in terms of diversity and basic composition of native invertebrate species (as described in Ahmat 1993; Jasinska and Knott 1994; Pinder 2002) taking account of natural change of the community over time. This will be measured as a loss of more than 10% of the native invertebrate species in any one spring over the life of the plan.
Decline in the condition of the habitat, in terms of loss of fringing buffer vegetation, increase in numbers of exotic species and other threatening processes as defined in this document. This will be measured as follows:

  • a decline in the area of buffer vegetation under conservation management adjacent to the springs of 10% or more,

  • increase in the cover of exotic plant taxa in the springs or buffer area of more than 10%,

  • groundwater levels and quality not maintained within the parameters expected as a consequence of natural change, by comparison with monitoring results for the Gnangara Mound in areas remote from development.

Summary of Recovery Actions:

1. Coordinate recovery actions

11. Design and conduct research

2. Map habitat critical to survival

12. Ensure hygiene conditions near the community

3. Clarify and continue to monitor the extent and boundaries of the community

13. Continue to monitor dieback

4. Liaise with current land owners, land managers and other interested groups

14. Monitor and implement weed control

5. Disseminate information

15. Rehabilitate recharge catchment zones and adjacent wetland areas

6. Monitor water levels and quality

16. Report on success of management strategies for tumulus springs

7. Manage water quality and quantity

17. Support reservation of Occurrence 2 and adequate buffer area

8. Monitor the flora and fauna of tumulus springs

18. Fence Occurrence 2

9. Develop and implement Fire Management Plans

19. Ensure visitor access-ways do not impact the tumulus springs

10. Ensure earthworks nears springs do not impact community

20. Block drain on southeast corner of Neaves Road Nature Reserve

1. BACKGROUND




1.1 History, defining characteristics of ecological community, conservation significance and status

The heavy clay soils of the Guildford Formation on the eastern side of the Swan Coastal Plain have been formed through the accumulation of deposits eroded from the hills of the Darling Range to the east. Between Bayswater and Muchea on the eastern extremities of the Bassendean Dune system, the tumulus (Latin meaning ‘little mound’) springs historically occurred where the sands and clays meet. The Bassendean sands contain the large superficial aquifer known as the Gnangara Mound. This groundwater is forced to the surface at a series of discharge points on the eastern boundary of the aquifer where waters encounter the relatively impervious Guildford clays. Discharge areas form springs, bogs, and swamps.


In the case of the tumulus springs, there is continuous growth of vegetation that causes the formation of peat around the permanent water supply. Water continues to penetrate the increasingly elevated peat layers due to the pressure created by local and regional hydrological forces. Where water finds a ‘preferred pathway’ or conduit through the soil, water movement is much faster than normal groundwater flow. Such conduits or pipes may carry sand and silt to the surface, where it is deposited as a ‘collar’ of increasing height, so enhancing the formation of mounds (A. Davidson1, personal communication).
Historically, the tumulus springs were common within their narrow range. The swamps, lakes, dams and springs form a north - south line parallel to the Darling Scarp, and corresponding to the junction between the Bassendean Sands and the Guildford Clays. Some of these groundwater discharge points are located within the western groundwater catchment of Ellen Brook. The tumulus springs have typically been excavated to create farm dams or cleared and sealed with limestone to provide pasture for horses and cattle.
The remaining vegetated tumulus springs have an overstorey of moisture adapted species including Melaleuca preissiana, Banksia littoralis, Agonis linearifolia and Eucalyptus rudis. Common understorey species include Agonis linearifolia, Pteridium esculentum, Astartea fascicularis and Cyclosorus interruptus. The following non-vascular plant species have also been located on peat mounds associated with the community (Jasinska and Knott 1994): Lycopodium serpentium (bog clubmoss), Riccardia aequicellularis, Jungermannia inundata, Goebelobryum unguiculatum and Hyalolepidozia longiscypha. Common weed species associated with the mounds include Isolepis prolifera (budding club-rush) and Pennisetum clandestinum (kikuyu).
The peat mounds may provide a permanently moist refuge for fauna that historically had a wider distribution. Consequently, relictual species may be protected from climatic changes and survive in these mounds. Some of these species may have no dormant period and would be killed if the mounds dried out (E. Jasinska personal communication2). Although there is a high level of heterogeneity in the fauna associated with mounds, common groups include Ostracoda, Nematoda, Acarina, Amphipoda, Cladocera, Copepoda, Decapoda, Oligochaeta, Annelida, Tardigrada, Turbellaria and Insecta.
The significance of the tumulus springs was recognised in the Conservation Through Reserves Committee recommendations (Department of Conservation and Environment 1983) that referred to sites just east and south of reserve 46622 on Faull Street, Muchea. Recommendation C25 referred to the need for survey, discussions with owners and a report on the conservation of the flora, and noted that ways to protect the conservation values should be sought. The same report also recommended that Geological Survey should investigate the hydrology of the area with a view to preventing adverse impact from local groundwater drawdown. None of the recommendations were implemented prior to 1996, and the springs and associated peat mounds have been progressively destroyed by grazing, levelling and packing with limestone, or have dried up (Jasinska and Knott 1994).
The integrated process of updating the ‘System 6’ Conservation Through Reserves System Recommendations (DEP 1997) and the Ministry for Planning Urban Bushland Strategic Plan, has resulted in Bush Forever (Government of Western Australia 2000). Occurrences 2, 3 and 4 are within the area covered by Bush Forever. While Occurrence 4 was only located and surveyed in 2004, after Bush Forever was published, the spring is contained within a Bush Forever site. Any proposed developments likely to adversely affect those occurrences will need to be assessed under the Bush Forever process (State of Western Australia 2000). Occurrence 1 is outside of the area covered by Bush Forever, but has been purchased as a conservation reserve.

Table 1 Extent and location of occurrences

Occurrence Number

Location

Estimated area of tumulus springs

Occurrence 1

Nature Reserve 46622, Faull Street, Muchea

1.4 ha

Occurrence 2

Private land, Ellenbrook

2 ha

Occurrence 3

Neaves Rd Nature Reserve, Bullsbrook

4 ha

Occurrence 4

Bush Forever Site, Bullsbrook

0.87 ha



Table 2 Vesting and tenure of occurrences

Occurrence Number

Vesting

Purpose

Tenure

Occurrence 1

Conservation Commission

Conservation of Flora and Fauna

Crown Reserve – Nature Reserve

Occurrence 2

Multiplex

Freehold – no purpose listed

Freehold – Non DEC Act

Occurrence 3

Conservation Commission

Conservation of Flora and Fauna

Crown Reserve-Nature Reserve

Occurrence 4

DPI/WAPC*

Conservation and Recreation

Freehold, Non-DEC

* Department for Planning and Infrastructure / Western Australian Planning Commission

Description of Occurrences

Intact tumulus springs (uncleared) are only known from four locations; a Nature Reserve on Faull Street in Muchea; Egerton Stud about 2 km south of the junction of Maralla and Halden Roads, Ellen Brook; Neaves Road Nature Reserve; and a Bush Forever site in Bullsbrook that is contiguous with the bushland that contains Neaves Rd Nature Reserve. These four remaining spring areas differ in structure of the mounds, presumably as a result of differences in hydrogeology or history of formation.


Occurrence 1 is in a Nature Reserve on Faull Street in Muchea and contains a series of boggy peat mounds that were historically up to two metres tall. Temporary pools occur where peat has been burnt. Water oozes from the soil, or flows out from discrete vertical channels from the peat mounds. Cattle grazed the area in the past, but have now been excluded by the erection of a fence around the reserve area. This site was previously privately owned, but was purchased in 1996 with joint DEC and Commonwealth funds, and is now a Nature Reserve.
The vegetation composition of the tumulus springs in the Faull Street Nature Reserve is likely to have been altered by grazing, as the area had apparently been intermittently grazed for many years. It is unknown to what extent fire has influenced the present structure or composition of the community. The combination of grazing and fire would almost certainly have increased the invasion of exotic species such as Pennisetum clandestinum and Isolepis prolifera into the community.
Occurrence 1 was burnt in a hot fire in 1995 and most of the understorey was destroyed. This created very open areas and led to massive weed invasion. However, monitoring in 2005 indicated that there was again a dense, impenetrable growth of ferns and few weeds in the spring area.
Occurrence 2 consists of a series of permanent springs flowing from a large area of peat mounds. Water oozes from the whole surface of the mounds and from discrete channels (Jasinska and Knott 1994). Low reeds, rushes, liverworts and club mosses cover the mounds. The dune to the west, covered with Banksia woodland, is probably part of the catchment. A pine plantation occurs further west again. The water from the springs forms a stream that then feeds into a dam.
The vegetation to the west of Occurrence 2, including the dune, is planned for residential development with approximately 3.6 ha of uncleared vegetation to be left within and surrounding the occurrence. The clearing and possible levelling of the dune may impact the hydrology of the mound springs as it is believed that the dune may currently contribute to the hydraulic pressure of the water flowing to the springs. The mound spring and associated small buffer is intended to be set aside as public land and will, initially at least, be vested with WAPC, and managed by DEC.
Occurrence 3 is located in the southern portion of Bush Forever site 97. It consists of a large series of mainly solid peat mounds with very small patches of bog (about 1 - 4 m2) immediately surrounding some of the more active spring discharges that support tall trees, bracken fern and dense mats of tall sedges. A narrow (1 - 4 m wide) strip of boggy ground provides shallow (1 - 10 cm deep) permanent water near the eastern margin of the spring area. Some of the peat mounds appear to have been burnt through and now occur as deep holes in the line of springs. The catchment is likely to include Banksia woodland on a dune to the west (within the Nature Reserve).
Occurrence 4 is located in the northwest corner of Bush Forever site 97. The spring is part of Bush Forever site 97 (immediately north of Neaves Nature Reserve and Occurrence 3). The property has been subdivided into two lots, with Lot 800, containing Occurrence 4, purchased by Western Australian Planning Commission (WAPC) in February 2004. Management of the bushland will be transferred to DEC in the future.
Occurrence 4 is more open and flat than the previous occurrences and contains no ferns. Vegetation consists mainly of Melaleuca preissiana over Agonis linearifolia, Astartea fascicularis, Baumea juncea and Baumea articulata. The bushland that contains occurrence 3 and 4 is contiguous and is contained within the same Bush Forever site.

Biological and ecological characteristics

The tumulus springs are permanently moist, and some are also associated with permanent pools and surface water. Many of the invertebrate animals and the vascular and non-vascular plant species present are adapted to this permanent moisture and the areas probably act as refugia from climate change (drying) for certain species (Jasinska and Knott 1994). Some of the invertebrate species do not have dormant stages and would not survive if the peat mounds were to dry out. In particular, Jasinska and Knott (1994) identified an amphipod that is the only known species of a newly discovered genus that is a Gondwanan relic, in the tumulus springs at Egerton. Water quality decline, for example through excessive nutrient input, is also a likely threat to the survival of some of the tumulus spring species.


Species lists, including vascular and non-vascular plants and invertebrates for the remaining intact mound spring areas are at Appendices 1, 2, and 3.
A number of non-vascular plants were historically recorded in Occurrence 1, and have more recently been located in Occurrence 2 (Jasinska and Knott 1994; see Appendices 1 and 2). Some of these taxa are significant as they usually only occur in the far south-west of the State (Jasinska and Knott 1994), but can occur in the spring areas as a result of the permanently moist microenvironment, and possibly due to other specific conditions associated with the sites. These taxa have not been recorded recently from the Faull Street reserve, possibly as a result of too frequent hot fires, grazing and other disturbances.
The presence of Hibbertia perfoliata in Occurrences 2 and 3 is of particular significance as it was historically recorded for the Swan Coastal Plain, but until recently was believed to have become extinct in that area (G. Keighery3 personal communication). It seems the taxon can only survive on the Swan Coastal Plain in permanently wet thickets where disturbance levels are relatively low. Such areas have almost completely disappeared from the Swan Coastal Plain although they are still relatively common in the Jarrah forest - a stronghold of Hibbertia perfoliata.

Hydrology

Hydrological information on the tumulus springs is somewhat limited as the hydrology has only been investigated in any detail at Occurrence 3. The springs are believed to be fed by a complicated network of conduits whose conformation has been determined by the geology of the stratum where the clays of the Guildford Formation interdigitate with the sands of the Bassendean Dunes. Evidence for the underground flow being in confined conduits is provided by large pieces of material, for example, the carapaces of crustaceans, that bubble up in the spring waters (E. Jasinska personal communication). Also, the pressure required to push water through the peat mounds could presumably only originate from confined flow and not from diffuse groundwater sources (J. Kite4; A. Davidson personal communication). The presence of complicated channels is inferred from the fact that springs have apparently dried up and re-emerged some distance away, when spring flow is interrupted. This can occur when springs are excavated (Ahmat 1993). This suggests the springs emanate from a series of channels, and diversion to an alternative path of least resistance can occur (Jasinska and Knott 1994). Also, anecdotal information indicates that during excavation of one spring area the earthworks exposed ‘rabbit burrow-like’ conduits carrying loose sand and water within the Guildford Clay layer.


The top of the Gnangara Mound is located to the west of the springs. Water flows in a number of directions from this point, including eastwards, and supplies the groundwater to the springs. It is essential that the level of the watertable in the Gnangara Mound provides an adequate head of pressure to drive the springs. The local hydrologic pressure created in parts of the aquifer within the dunes adjacent to each of the spring areas is also likely to be significant in terms of maintaining the spring flow (E. Jasinska, A. Davidson personal communication). Rainfall falling on the dunes adjacent to the springs would be involved in recharge of the local conduits feeding the springs (E. Jasinska, A Davidson personal communication). The maintenance of the flora and fauna of the tumulus springs is therefore also likely to depend on maintaining the quality of the water of the Gnangara Mound and of the local water mounds in dunes adjacent to each of the spring areas.
A trend of falling water tables in the general area is evident since around 1976 (Greay 1993). A corresponding decline in annual rainfall since around 1976 has contributed to this lowering of watertables, by contributing to drawdown of the superficial aquifer, the Gnangara Mound to the west. The previous owner of the recently gazetted reserve on Faull Street, Muchea noted that some of the springs on the property had dried up in living memory, probably as a result of decline of the water table (Ahmat 1993).
The area in which the tumulus springs occur is characterised by much valued heavy soils, which were historically extensively cleared for agriculture. Clearing is likely to have increased surface runoff and recharge of the groundwater in the localised area and may have acted to counteract drawdown to some extent. The springs on the Faull Street reserve are located on the Muchea townsite lots. There is little uncleared vegetation remaining there, however, so that additional recharge of the superficial aquifer as a result of further clearing for development in the localised area is unlikely. Changes in the level of the water table are very likely to influence the hydrology of these wetlands as they are likely to be almost entirely dependent on groundwater for water supply. This issue is discussed further under threatening processes.
The groundwater supplying Occurrence 1 is likely to flow mainly from the west, and possibly with some contribution of flow from the north (E. Jasinska personal communication). The main water supply for the springs within the reserve is likely to be deep below the surface and from the local water mound in the denuded dune to the west that is also part of the Nature Reserve (A. Davidson personal communication). Land management practices on this land and possibly other land adjacent to the west therefore have the potential to influence the quality and quantity of water supplied to these springs. Deep-rooted vegetation such as trees that originally occurred on the dune in the reserve would probably have drawn relatively large quantities of water from this local groundwater mound. A balance between loss of water through transpiration and gaining water through increased infiltration needs be determined for appropriate management of these dunes. Such hydrologic considerations needs to be considered in planning the revegetation of such dunes.
A line of highly degraded peat mounds occurs to the north of the reserve area that contains Occurrence 1 and links to those on the reserve. A dense area of the non-local tree, Eucalyptus camaldulensis (river gum) occurs on these peat mounds and may be drawing larger quantities of water than the original vegetation.
The supply of groundwater to the tumulus springs at Occurrence 2 is likely to be mainly from the west, with the pressure head and recharge being supplied by the dune to the west of the springs (E. Jasinska, A. Davidson personal communication). A seasonal wetland occurs to the east of this dune, with the tumulus springs further east again. Groundwater flowing from the dune is likely to move in the general direction of the wetland in between the springs and the dune, and on towards the springs, confined under clay layers within conduits (E. Jasinska personal communication). Residential development is currently proposed for the area and it is likely that the dune will be levelled or removed. Major earthworks that may sever conduits supplying water to the springs, and abstraction of groundwater in the vicinity of the dune, the seasonal wetland or within the spring area have the potential to severely disrupt water supply to these tumulus springs.
The supply of groundwater to Occurrence 3 appears likely to be mainly from the west. Groundwater abstraction near the springs, or within the springs themselves, has the potential to severely affect flows. Preliminary study by S. Burton5 (Groundwater Consulting Services 2002) has found that the spring overlies at least 5m of clean quartz sand (Bassendean Sand), which grades into silt of the Guildford Formation in the eastern part of the Reserve. A layer of peat occurs throughout the low lying area, and can be up to 4m thick (but averages 1 to 1.5m thick). Two discrete aquifers occur within the spring area, separated by an unidentified low-permeability unit. High groundwater levels occur to the west in an unconfined sandy aquifer, which is probably recharged by direct infiltration of rainfall, where Banksia woodland occurs on a dune (A. Davidson personal communication). This aquifer appears to contribute to spring flow based on groundwater table elevations. Groundwater levels in the east (in the sand aquifer underlying the peat) range from over 1m below ground to 0.3m above ground, and are below the elevation of the spring. Seasonal changes in groundwater levels may induce discharge in other areas (Groundwater Consulting Services 2002).

Habitat critical to the survival of the community, and important occurrences

The habitat critical for survival of the Mound Springs community comprises:



  • the area of occupancy of known occurrences;

  • areas of similar habitat within 200 metres of known occurrences, i.e. areas of continuous discharge of groundwater in raised areas of peat at the junction between the Bassendean Sands and the Guildford clays;

  • remnant vegetation that surrounds or links occurrences (this is to provide habitat for pollinators or to allow them to move between occurrences); and

  • the local catchment for the surface and groundwater that maintain the habitat of the community (the community would be dependent on maintenance of the local and regional hydrological conditions).

Given that the community is listed as Critically Endangered, it is considered that all occupied habitat is critical to the survival of this community, and all known occurrences are important.



Benefits to other species/ecological communities

Recovery actions implemented to improve the quality or security of the community are likely to improve the status of any species within the community. No associated species are separately listed as Threatened under State or Commonwealth legislation.


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. The community is not listed under any specific international treaty, however, and therefore this recovery plan does not affect Australia’s obligations under any other international agreements.

Role and interests of indigenous people

An Aboriginal Sites Register is kept by the Department of Indigenous Affairs, and lists one camp site occurring in the vicinity of Occurrence 2. Implementation of recovery actions under this plan includes consideration of the role and interests of indigenous communities in the region.



Social and economic impacts

Occurrence 2 is located on private property that is currently under residential development. Negotiations with the private owner resulted in the mound springs and a small area surrounding it to be set aside as public open space. Negotiations will continue with the land owner to help protect the occurrence.


Occurrence 4 occurs adjacent to private property where an annual four wheel drive Gymkhana is held which could have adverse affects on water quality at the springs. Negotiations will continue with the adjacent land managers and regulatory authorities with respect to the future activities and impacts to this occurrence.
The implementation of this recovery plan has the potential to have some social and economic impact, where occurrences are located on and adjacent to private property. Recovery actions refer to continued liaison between stakeholders with regard to these areas.

Affected Interests

Occurrences of the Organic Mound Springs are within the Local Government Authority of the City of Swan. They occur on land managed by DEC, the WAPC, and on private land. Potentially affected landholders are the developers of land on which Occurrence 2 occurs, and possibly the owners of land adjacent to all occurrences, but Occurrence 4 in particular.



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