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 IRP 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.

Historical and current threatening processes

Clearing

Clearing for agriculture has been extensive on the heavy soils on the eastern side of the Swan Coastal Plain, with some 97% of all vegetation in the area cleared historically (Keighery and Trudgen 1992; CALM 1990). In particular, the tumulus springs on heavy soils were often perceived as a nuisance to farming practices as they were excessively wet and boggy. Consequently, almost all of these springs have been cleared, levelled, packed with limestone and planted with kikuyu grass, excavated and dammed, or the spring brooks dammed (Ahmat 1993).

Occurrence 1 is now contained within a reserve that is under the care, control and management of the Conservation Commission for ‘Conservation of Flora and Fauna’. Occurrence 2 is planned to be set aside as Open Space adjacent to an extensive urban development. Occurrence 3 was purchased with DEC and Commonwealth Government funds and is now part of the Neaves Road Nature Reserve. Occurrence 4 has been purchased by the WAPC as part of a Bush Forever site. It is planned that in future the bushland that contains Occurrence 4 will be managed by DEC.
Dunes of varying sizes occur on the western side of three of the four remaining vegetated tumulus spring areas. Each of these is likely to provide important recharge areas, and to be involved in providing the hydraulic pressure head for the adjacent spring area. In addition, two of the dunes adjacent to spring areas are still vegetated (Occurrences 2 and 3) and vegetation is likely to be important for moisture retention and water percolation into the sands. However, the Banksia woodland vegetation on the dune to the west of Occurrence 2 is to be cleared and this may alter the hydrology of the springs, as may the possible levelling of the dune, as mentioned. Vegetation, especially deep rooted plants such as trees, would draw on the local groundwater where roots could tap into this source.
In the case of Occurrence 1 the dune to the west has been largely denuded by a combined process of grazing and possibly dieback deaths and drought. Under normal circumstances, rainfall intersecting the dune surface contributes to recharge of the local groundwater mounds. However, the sands can become hydrophobic when dry and in the absence of vegetation, or following destruction of vegetation by fire (A. Davidson, E. Jasinska personal communication). In this situation, most of the rainfall would drain off the dune as surface runoff and therefore not contribute to the groundwater recharge. Regrowth of native vegetation may help enhance penetration of rainfall in these circumstances (A. Davidson, personal communication).
Plant species can also contribute to the hydrophobic nature of soils (A. Davidson, personal communication). Introduced grasses, such as Veldt grass (Ehrharta calycina) that has established in the reserve containing Occurrence 1, causes soils to repel water and should be kept away from the spring areas themselves and the adjacent dunes.

Water levels
The flora and fauna that inhabit the tumulus springs are likely to be entirely dependent on the permanent supply of fresh water (E. Jasinska, personal communication). As mentioned, some of the tumulus springs in reserve 46622 on Faull Street have dried up relatively recently. This is possibly due to local groundwater drawdown, but is probably exacerbated by declining rainfall due to climate change, and an overall decline in the Gnangara Mound that feeds the springs.
There are currently no obvious large groundwater abstraction occurring in the springs’ recharge zone (J. Kite, personal communication). Conservation of the discharge areas of each of the springs requires continuing function of the recharge areas to provide adequate water of appropriate high quality (Ahmat 1993). Controls on groundwater abstraction and minimising pollution of the groundwater, exercised through planning and impact assessment, are therefore essential for the conservation of the springs.
As mentioned in the previous section, proposed clearing of vegetation and possible levelling of the dune west of Occurrence 2, as part of a residential development, has the potential to alter the hydrology of this spring area.
Actual groundwater use (i.e. timing and amount of groundwater abstraction), in the vicinity of each of the spring areas needs to be determined. Significant groundwater use close to the springs has the potential to impact the springs as a consequence of groundwater drawdown.
Water quality
Where animal droppings and other nutrient sources can contaminate surface or groundwater entering the springs, enhanced nutrient levels are likely to favour weed invasion and possibly alter water quality such that some components of the fauna cannot survive. Nutrient input is most likely to be from very localised areas in the case of surface flow into the springs, so landuse in areas close to the springs may also be very important for conservation of the water quality. On the other hand it may be possible for sources of pollution to enter the groundwater that eventually enters the springs from sources much more distant.
Some activities associated with a four wheel drive Gymkhana event that occurs adjacent to Occurrence 4 have the potential to adversely impact water chemistry. The event involves excavations for water traps, possibly into the shallow groundwater table. The traps are within 45 meters of the boundary of Occurrence 4 and hydrocarbon contamination of the water in these traps is likely to directly affect water quality through hydraulic connection with the groundwater (S. Burton personal communication). Hydrocarbon contamination is possible by driving vehicles with oily engine bays through water traps, washing down of vehicles, refuelling and servicing spills or inappropriate disposal or losses through vehicle impact or other damage.

Grazing

The tumulus springs of Occurrence 1 have been subject to intermittent grazing, as they were previously located in a paddock that supplied permanent rich pasture. Grazing is likely to have caused alterations to the species composition through the selective grazing of edible species, the introduction of weeds as a consequence of disturbance and increased nutrients from animal droppings, and through general disturbance. This may well have contributed to the decline of non-vascular plants that were recorded historically in Occurrence 1 (refer Appendix 1).

Occurrence 2 does not appear to have been grazed historically (G. Keighery personal communication).
The tumulus springs on Occurrence 3 may have historically been subject to grazing, but no stock are currently kept in the fenced area adjacent to the springs. This spring area is covered in extremely dense vegetation that would be relatively impenetrable to stock. Following fires, however, the dense vegetation cover would have been destroyed, and stock would have been able to graze the area. This occurrence is now fenced from stock.
Occurrence 4 may have been accessible to stock prior to purchase in 2004. Following the purchase of the land, the spring and vegetated buffer were re-fenced in April 2004 to exclude stock.

Increased weed invasion

As mentioned above, grazing alters species composition through selective foraging, and causes increased weed invasion. The two major weed species in the tumulus springs in the Faull Street reserve are Isolepis prolifera (budding club-rush) and Pennisetum clandestinum (kikuyu). The tumulus springs of Occurrence 3 are relatively weed free, but weeds are encroaching at specific points, possibly where levels of disturbance have historically been higher. Rubus sp. (blackberry) and Ficus carica (fig) occur immediately adjacent to the springs and some Isolepis prolifera occurs on the mounds themselves.

A weed control program is necessary to maintain or improve the current condition of occurrences of the community in the long term. Panetta and Hopkins (1991) state that the aims of weed control are to maintain the pre-invasion condition of the habitat (prevention); control or arrest ongoing weed invasion (intervention); and reverse the degraded condition of the habitat where applicable (rehabilitation).
The highest priority will be to control weeds, in the early stages of invasion where possible, that pose the greatest threat to the community, e.g. Isolepis prolifera at Occurrence 3, some perennial grass weeds and Watsonia. Appropriate methods of weed control are found in Brown and Brooks (2002) and may include hand weeding or localised application of herbicide.

Altered fire regimes

Fires are likely to have a significant effect on vegetation composition in Mediterranean ecosystems (Abbott and Burrows 2003). It is also likely that the fire regime around each of the spring areas has been altered since European settlement, especially those located in agricultural areas (Occurrences 1, 3 and 4). Stratigraphic coring of the peat would help elucidate the fire history of these springs.

The wetland vegetation associated with the springs is likely to be less adapted to very hot fires than upland vegetation as the sites are permanently moist and are unlikely to have burnt as readily. In addition, the build up of peat makes the areas very prone to fires that occur in very dry seasons that are capable of destroying the peat mounds themselves. An increase in the frequency of hot fires is likely to pose a significant threat to the wetland-adapted flora and fauna.
As this community is not well studied, little is known of the community’s requirements in terms of fire regime to maintain plant species composition. As fires can destroy the peat mounds, however, it can be assumed that conservation of the communities depends on hot fires being excluded during seasons when the mounds are drier and are flammable.
The risk of fire is increased by the presence of grassy weeds in the understorey at the Faull Street reserve site (Occurrence 1), as they are likely to be considerably more flammable than the original native species in the understorey.

Dieback

It is not known if the community type is susceptible to dieback disease caused by Phytophthora species. However, the plants that inhabit the tumulus springs themselves are largely species that are thought not to be sensitive to dieback. In particular, Melaleuca preissiana and the sedges that dominate the community are not dieback sensitive (Helyar 1994). Hibbertia perfoliata is listed as a dieback indicator on the Swan Coastal Plain by Helyar (1994), however, and therefore may be susceptible to the disease in that area.

Banksia woodlands occur on the dunes to the west of Occurrences 1, 2 and 3. As mentioned, these dunes are likely to be important in maintaining the local hydrology of the springs. Banksia trees are deep rooted species that are likely to draw on local groundwater. Banksia communities are very susceptible to dieback caused by Phytophthora species and are often severely affected by its introduction. Loss of Banksia and other dieback susceptible species may actually increase local groundwater recharge unless they are replaced with species that increase the hydrophobic nature of the soil, as has occurred at the Faull Street reserve with the introduction of Veldt-grass. Dry, bare sand as occurs in parts of the dune adjacent to Occurrence 1 is also strongly hydrophobic, however. Replacement of the Banksia woodlands adjacent to the springs with species that use more water, such as taller trees, may also impact the springs through drawdown of the groundwater table.
The dune to the west of the springs in the Faull Street reserve has been severely degraded, presumably initially through clearing, then from continued loss of juvenile plants through grazing. Dieback may also have impacted the Banksia community by killing mature and juvenile individuals of susceptible species.
Risk of introduction or further spread of disease will be minimised by ensuring good hygiene procedures at all occurrences. This would help ensure that current hydrological regimes are maintained in groundwater in dunes close to the springs. Such hygiene procedures involve washdown of any equipment and footwear prior to undertaking works in the remnant vegetation surrounding the community, as well as within the springs themselves.

Evaluation of the Plan's Performance

DEC, in conjunction with the Swan Region Threatened Flora and Communities Recovery Team will evaluate the performance of this Interim Recovery Plan. The plan is to be reviewed within five years of its completion.

Conservation status

The community meets the following criteria for Critically Endangered (CR) ecological communities in Western Australia:

B) Current distribution is limited, and the following apply (i, ii):
i) geographic range and/or number of discrete occurrences, and/or area occupied is highly restricted and the community is currently subject to known threatening processes which are likely to result in total destruction throughout its range in the immediate future (within approximately 10 years);
ii) there are very few occurrences, each of which is small and/or isolated and extremely vulnerable to known threatening processes.

1.3 Strategy 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 the condition of the community.