Coastal Upland Swamp in the Sydney Basin bioregion - proposed endangered ecological community listing

NSW Scientific Committee - preliminary determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Preliminary Determination to support a proposal to list Coastal Upland Swamp in the Sydney Basin bioregion as an ENDANGERED ECOLOGICAL COMMUNITY on Part 3 of Schedule 1 of the Act. The listing of Endangered Ecological Communities is provided for by Part 2 of the Act.

 

The Scientific Committee has found that:

1. Coastal Upland Swamp in the Sydney Basin bioregion is the name given to the ecological community in the Sydney Basin bioregion associated with periodically waterlogged soils on Hawkesbury sandstone plateaus, generally where mean annual rainfall exceeds 950 mm. Soils that support Coastal Upland Swamp are acidic and vary from yellow or grey mineral sandy loams with a shallow organic horizon to highly organic spongy black peats with pallid subsoils. They vary in depth from a few centimetres to at least four metres. The vegetation is dominated by sclerophyll shrubs and/or sedges, with dynamic mosaics of structural forms that may include tall scrub, open heath and/or sedgeland. Although typically treeless, Coastal Upland Swamp may include scattered trees. In NSW all sites are within the Sydney Basin Bioregion (sensu Thackway & Cresswell 1995).

2. Coastal Upland Swamp in the Sydney Basin bioregion is characterised by the following assemblage of species:

Actinotus minor

Almaleea paludosa

Baeckea imbricata

Baeckea linifolia

Banksia ericifolia

Banksia oblongifolia

Banksia robur

Bauera microphylla

Baumea acuta

Baumea teretifolia

Blandfordia nobilis

Boronia parviflora

Burchardia umbellata

Cassytha glabella

Chorizandra sphaerocephala

Cryptandra ericoides

Dampiera stricta

Dillwynia floribunda

Drosera binata

Drosera spathulata

Empodisma minus

Entolasia stricta

Epacris microphylla

Epacris obtusifolia

Epacris paludosa

Eurychorda complanata

Gahnia sieberiana

Gleichenia microphylla

Gonocarpus micranthus

Gonocarpus salsoloides

Gonocarpus tetragynus

Goodenia dimorpha

Grevillea oleoides

Grevillea parviflora

Gymnoschoenus sphaerocephalus

Haemodorum corymbosum

Hakea teretifolia

Hibbertia serpyllifolia

Lepidosperma limicola

Lepidosperma neesii

Leptocarpus tenax

Leptospermum grandifolium

Leptospermum juniperinum

Leptospermum squarrosum

Lepyrodia scariosa

Lindsaea linearis

Melaleuca squarrosa

Mirbelia rubiifolia

Mitrasacme polymorpha

Opercularia varia

Petrophile pulchella

Plinthanthesis paradoxa

Ptilothrix deusta

Pultenaea aristata

Schoenus brevifolius

Schoenus lepidosperma subsp. pachylepis

Schoenus paludosus

Selaginella uliginosa

Sowerbaea juncea

Sphaerolobium vimineum

Sprengelia incarnata

Stackhousia nuda

Stylidium lineare

Symphionema paludosum

Tetraria capillaris

Tetrarrhena turfosa

Thysanotus juncifolius

Viminaria juncea

Xanthorrhoea resinosa

Xanthosia tridentata

Xyris gracilis subsp. laxa

Xyris juncea

Xyris operculata

 

 

3. The total species list of the community is larger than that given above, with many species present in only one or two sites or in low abundance. Keith & Myerscough (1993) recorded more than 170 vascular plant species in Coastal Upland Swamp within O’Hares Creek catchment alone, with the total vascular flora of the community likely to exceed 200 species. The species composition of a site will be influenced by the size of the site, recent rainfall or drought conditions and by its disturbance (including grazing, land clearing and fire) history. The number and relative abundance of species will change with time since fire, and may also change in response to changes in fire frequency or grazing regime. At any one time, above-ground individuals of some species may be absent, but the species may be represented below ground in soil seed banks or as dormant structures such as bulbs, corms, rhizomes, rootstocks or lignotubers. The list of species given above is of vascular plant species, however the community also includes micro-organisms, fungi, cryptogamic plants and a diverse fauna, both vertebrate and invertebrate.

4. Coastal Upland Swamp in the Sydney Basin bioregion is characterised by highly diverse and variable mosaics of vegetation related to variability in soil conditions and fire regimes. A number of studies (Buchanan 1980; Keith & Myerscough 1993; NPWS 2003) have recognised several sub-communities within the Coastal Upland Swamp community. Larger swamps of the community are characterised by distinctive mosaics of multiple sub-communities that may include a range of structural forms including tall open scrubs, tall closed scrubs, closed heaths, open graminoid heaths, sedgelands and fernlands. Smaller swamps are more typically characterised by open graminoid heaths and/or sedgelands, but may include tall scrubs. Trees are typically absent from the community, but may be present as scattered individuals or clumps of mallee or arborescent eucalypts.

5. The most waterlogged zones of the larger swamps have deep peaty, gleyed soils and tend to be dominated by various combinations of Leptospermum juniperinum, L. grandifolium, Melaleuca squarrosa, Banksia robur and Epacris paludosa, often with a dense layer of Gleichenia spp. and/or sedges including Gahnia sieberiana, Baumea teretifolia, Chorizandra sphaerocephala and Empodisma minus, and the grass Tetrarrhena turfosa. In some locations the woody species are sparse and the vegetation comprises ferns and sedges. In zones where the water table is less frequently sustained near the surface, the peaty soil horizon is shallower, with more mineral content, and the vegetation is more typically an open graminoid heath dominated by an open layer of shrubs that may include Banksia robur, Leptospermum juniperinum, Almaleea paludosa and/or Hakea teretifolia, sometimes with Banskia ericifolia. A dense matrix between the shrubs is dominated by large cyperaceous sedges that may include Lepidosperma limicola, Chorizandra sphaerocephala, Baumea teretifolia, Gymnoschoenus sphaerocephalus and Schoenus brevifolius, and the woody non-arborescent grass tree Xanthorrhoea resinosa. Smaller sedges, cord rushes, such as Empodisma minus, Lepyrodia scariosa and Leptocarpus tenax, grasses, Entolasia stricta and Tetrarrhena turfosa, and forbs including Xyris operculata, may also be present in variable abundance. The vegetation of the least frequently waterlogged zone is highly variable depending on subtle soil characteristics and fire history. These zones tend to dominate smaller swamps and the periphery of larger swamps. The soils are predominantly mineral, with variable proportions of quartz sand grains and clay, depending on parent material, usually with humic staining near the surface, and bedrock at variable depth. The vegetation may include several sub-communities, including highly species-rich open graminoid heath, sedgeland and tall scrub. Patches of open heath are often dominated by Banksia oblongifolia, B. paludosa and/or Hakea teretifolia with a wide range of other shrubs including Baeura microphylla, Dillwynia floribunda, Epacris obtusifolia, Xanthorrhoea resinosa and Grevillea oleoides. The matrix between shrubs comprises a variety of small sedges, cord rushes, ferns and forbs, including Ptilothrix deusta, Lepidosperma neesii, Schoenus brevifolius, Lepyrodia scariosa, Leptocarpus tenax, Entolasia stricta, Plinthanthesis paradoxa, Lindsaea linearis, Dampiera stricta, Goodenia dimorpha, Mitrasame polymorpha, Burchardia umbellata, Sowerbaea juncea, Cassytha glabella, Gonocarpus spp. and Drosera spp. In some patches larger shrubs are sparse or absent and the vegetation is characterised by smaller shrubs such as Baeckea imbricata, Epacris obtusifolia and Sprengelia incarnata with smaller sedges, cord rushes, grasses and forbs, notably Schoenus paludosus, Lepidosperma filiforme, Boronia parviflora and Symphionema paludosum. Depending on fire history and seed dispersal, some patches in the less frequently waterlogged zones may develop into dense thickets dominated by tall shrubs including Banksia ericifolia, Hakea teretifolia and Leptospermum squarrosum. As these thickets develop with time since fire the layers of smaller shrubs and sedges tend to become sparser and less diverse (Keith & Bradstock 1994; Keith et al. 2007). Boundaries between Coastal Upland Swamp and adjacent communities may be quite distinct across distances of a few metres or more diffuse transitions across tens of metres, and may not follow treelines precisely (Keith pers comm. 2011).

6. Coastal Upland Swamp in the Sydney Basin bioregion provides habitat to a wide variety of birds, mammals, amphibians, reptiles and invertebrate species. Some typical mammal and bird species include the swamp wallaby (Wallabia bicolor), Brown Antechinus (Antechinus stuartii), Swamp Rat (Rattus lutreolus), New Holland Honeyeater (Phylidonyris novaehollandiae), Southern Emu-wren (Stipiturus malachrus), Grey Fantail (Rhipidura albiscapa) and Beautiful Firetail (Stagonopleura bella). The Australian Crayfish (Euastacus australasiensis), the Hairy Crayfish (E. hirsutus) and the Sydney Crayfish (E. spinifer) are abundant and distinctive inhabitants of Coastal Upland Swamp. Stygofauna within the groundwater are abundant and comprise relatively few co-occurring species, but these exhibit high levels of local endemism (Hose 2008, 2009). Threatened species that have been recorded in the community include the Vulnerable Pultenaea aristata, Acacia baueri subsp. baueri, Giant Burrowing Frog (Heleioporus australiacus), Red-crowned Toadlet (Pseudophryne australis), Rosenberg's Goanna (Varanus rosenbergi) and the Endangered Green and Golden Bell Frog (Litoria aurea). The Eastern Ground Parrot (Pezoporus wallicus wallicus) was once common on Maddens Plains and was thought to be locally extinct until recently rediscovered within upland swamp landscapes of Woronora River catchment. The community also provides habitat for the Endangered Giant Dragonfly (Petalura gigantea), which is now very uncommon in coastal regions.

7. Coastal Upland Swamp in the Sydney Basin bioregion includes: ‘Sedge swamps’ and ‘Shrub swamps’ of Pidgeon (1938); ‘Extensive Swamp or Moor Communities’ of Davis (1941); ‘Swamps’ of Buchanan (1980); ‘Sedgeland’ (Community 12) of Benson & Fallding (1981); ‘Sedgeland/Shrubland’ (Community 21) of Thomas & Benson (1985) [reproduced in Benson & Howell (1994)]; ‘Open-scrub (Community 4a), ‘Open-heath’ (community 4b) and ‘Sedgeland’ (Community 5) of Fallding & Benson (1985); ‘Ti-tree Thicket’ (TT), ‘Cyperoid Heath’ (CH), ‘Restioid Heath’ (RH), ‘Sedgeland’ (SL) and ‘Banksia Thicket’ (BT) of Keith & Myerscough (1993) and Keith (1994); Upland Swamps Banksia Thicket (MU42), Upland Swamps Tea-tree Thicket (MU43) and Upland Swamps Sedgeland-Heath Complex (MU44) of NPWS (2003); ‘Sydney Hinterland Sandstone Upland Swamp’ (MU43) of DECC (2008a); ‘Coastal Upland Damp Heath Swamp’ (map unit S_FrW01) and ‘Coastal Upland Wet Heath Swamp (map unit S_FrW02) of DECCW (2009)’; ‘Coastal Upland Swamp’ (map unit FrWp129) and parts of ‘Blue Mountains - Shoalhaven Hanging Swamps’ (map unit FrWp130) of Tozer et al. (2010). These latter two units tend to intergrade on the Woronora Plateau (Tozer et al. 2010), with overall floristic differences relating to increasing plant diversity as altitude declines and some local endemism in the upper altitudinal range of Blue Mountains - Shoalhaven Hanging Swamps (FrW p130). Various other published and unpublished studies have also recognised Coastal Upland Swamp as a distinctive community.

8. Related ecological communities currently listed under the Threatened Species Conservation Act 1995 include Blue Mountains Swamps in the Sydney Basin Bioregion (Vulnerable), Newnes Plateau Shrub Swamp in the Sydney Basin Bioregion (Endangered) and Montane Peatlands and Swamps of the New England Tableland, NSW North Coast, Sydney Basin, South East Corner, South Eastern Highlands and Australian Alps bioregions (Endangered). All three communities are types of upland swamp. Blue Mountains Swamps and Newnes Plateau Shrub Swamp share some plant species with Coastal Upland Swamp, and are also found in headwaters of streams on Sydney sandstone plateaus (although both occur primarily on sandstones of the Narrabeen Group cf. Hawkesbury Formation). Coastal Upland Swamp usually contains a much higher diversity of plant species than these other communities (Keith & Myerscough 1993) and therefore many of its dominant and less common species are not found in either Blue Mountains Swamps or Newnes Plateau Shrub Swamp (e.g. Banksia robur, B. oblongifolia, Grevillea parviflora, Pultenaea aristata, etc.). Montane Peatlands and Swamps share some geomorphic and hydrological characteristics but relatively few species in common with Coastal Upland Swamp. The former are found on more fertile non-sandstone substrates, generally in cooler climatic environments, and lack many of the sclerophyllous floristic components which characterise the other three swamp communities.

9. Coastal Upland Swamp in the Sydney Basin bioregion occurs primarily on impermeable sandstone plateaus in the headwater valleys of streams and on sandstone benches with abundant seepage moisture (Buchanan 1980; Young 1986; Keith & Myerscough 1993; Keith et al. 2006). Buchanan (1980) described three physiographic types: valley-floor swamps; valley-side swamps and composite swamps. Occasionally they may be associated with weathered shale lenses and ironstone (Buchanan 1980; Keith 1994) and there are uncommon examples along the lower reaches of some streams, for example tributaries of Marley Lagoon in Royal National Park. Elevation varies from about 20 m to over 600 m above sea level, although the majority of swamps occur within 200 – 450 m elevation.

10. There are strong hydrological controls on the local and regional distribution of the Coastal Upland Swamp. Its development is driven by positive feedbacks that operate when there is a substantial excess of precipitation over evaporation which promotes soil waterlogging in tandem with high run-on from their catchments and low rates of percolation and run-off (Young 1982, 1986). Lateral transportation and deposition of sediment by overland flow leads to choking of headwater valleys, impeding drainage. Higher levels of soil moisture lead to increased density of ground vegetation, trapping more sediment, further impeding drainage and killing trees, which are unable to tolerate raised water tables. Recurrent fires may further accelerate loss of trees and hydrological change, as these affect both the survival of existing trees and recruitment of new trees depending on soil moisture conditions soon after fires occur (Keith et al. 2006). Substantial shifts may occur in the boundaries between swamps and adjoining woodlands over decadal time scales (Keith et al. 2010). The loss of trees reduces the transpiration capacity of the vegetation, allowing the water table to rise to the surface more frequently than it would if trees were actively extracting groundwater (Keith et al. 2006). Recruitment of trees results in the opposite effect. While low surface gradients influence the moisture budget through slow rates of run-off, the swamps occasionally occur on steeper slopes where highly impermeable sandstone strata bring a large excess of seepage moisture to the surface where they outcrop on valley sides.

 

11. Regionally, the distribution of Coastal Upland Swamp in the Sydney Basin bioregion shows a strong relationship to climatic gradients. The community reaches its greatest development on the central eastern portion of the Woronora plateau, which also represents the greatest extent and oldest recorded occurrence of upland wetlands on the Australian mainland (Keith et al. 2006). Here, the Illawarra escarpment produces orographic rainfall and fogs, as well as enhanced cloud cover, which reduces evaporation. Gentle topographic gradients in this area, combined with the impermeable sandstone substrate, further promote surface waterlogging and swamp development. The orographic climatic effects diminish rapidly with distance inland from the escarpment, such that occurrence of swamps is rare on the western third of the plateau. Swamps become very restricted in areas receiving less than 950 mm mean annual rainfall, with limited occurrences in drier areas mediated by the balance between rainfall and evapotranspiration, surface slope, substrate permeability and seepage moisture. On the northern side of Sydney, highly restricted examples of upland swamp vegetation occur on the Hornsby Plateau on the Lambert Peninsula and around Calga-Kariong, extending as far west as the Great North Road in Yengo National Park (DECC 2008a).

12. Coastal Upland Swamp in the Sydney Basin bioregion is endemic to NSW within the eastern Sydney Basin from the Somersby district in the north to the Robertson district in the south. The distribution is divided into two portions separated by an area of less elevated terrain, lower rainfall, non-sandstone substrates and urban development in the eastern Sydney metropolitan area. In the north, the community occurs on the Somersby-Hornsby plateaus, in the south it occurs on Woronora plateau. It is currently known from the local government areas of Campbelltown, Gosford, Hornsby, Ku-ring-gai, Lane Cove, Manly, Pittwater, Sutherland, Warringah, Wingecarribee, Wollondilly, Wollongong and Wyong, but may occur elsewhere within the bioregion.

13. Examples of Coastal Upland Swamp in the Sydney Basin bioregion are represented within Brisbane Water, Garigal, Heathcote, Ku-ring-gai Chase, Lane Cove, Popran, Sydney Harbour, Royal and Yengo National Parks, Dharawal and Muogamara Nature Reserves, and Dharawal and Garawarra State Conservation Areas. Many of these reserves contain only a few hectares of the community.

14. Approximately 5360 ha of Coastal Upland Swamp in the Sydney Basin bioregion have been mapped based on an amalgamation of best available regional vegetation mapping throughout the range of the community (NPWS 2000, DECCW 2009, Tozer et al. 2010). Approximately 83% of this area occurs on the Woronora Plateau. The size of mapped swamps is highly skewed, with the largest 5% of swamps (>14 ha) accounting for just less than half (47%) of the total area of the community. Large swamps also contribute disproportionately to species diversity and hydrological function, due to their large volumes of peaty sediments that contribute sustained high-quality flows to discharge streams and their diverse array of habitat mosaics that encompass suitable conditions for a wide array of species.

15. Based on a 2 x 2 km grid, the spatial scale recommended by IUCN (2010) for assessing species’ areas of occupancy, the Area of Occupancy of Coastal Upland Swamp is estimated to be approximately 1140 [1100-1200] km2. Based on a minimum convex polygon enclosing all mapped occurrences of the community, its Extent of Occurrence is estimated to be 4960 [4730-5200] km2. The estimated Extent of Occurrence for Coastal Upland Swamp is consistent with a highly restricted distribution.

16. Areas of Coastal Upland Swamp in the Sydney Basin bioregion destroyed by clearing are likely to account for up to 10% of the historical extent of the community, although precise estimates of the reduction are currently unavailable. These areas include swamps cleared during construction of freeways, access roads, railway easements and fire trails, clay and sand quarries, surface facilities associated with underground mines, coal refuse emplacements, recreational facilities such as golf courses, and some early agricultural enterprises. Most of this habitat loss occurred after 1970 (Keith in litt. 2010). The scope for future habitat loss due to clearing is limited, as much of the remaining distribution is on public land managed by Sydney Catchment Authority and the National Parks and Wildlife Service. However, on unprotected tenures there remains a localised risk of clearing associated with rural and residential development, quarrying of clay and sand and specialised facilities such as rifle ranges. Future habitat loss may also be associated with specific developments involving transport, energy or water supply infrastructure and surface facilities associated with underground mining, which are sometimes permitted on protected tenures. Disturbances associated with earthworks within swamps or their catchments, such as changes to drainage, sedimentation and weed invasion, may also affect localised areas of the community. ‘Clearing of native vegetation’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

17. Three strands of evidence suggest that the distribution of Coastal Upland Swamp in the Sydney Basin bioregion is highly sensitive to changes in climatic moisture. Firstly, there is a lack of evidence that upland swamps existed in the region under drier climates that prevailed prior to the late Pleistocene era (Young 1986; Kodela & Dodson 1989). Secondly, there are strong contemporary spatial relationships between the distribution of swamps and perched aquifers that underpin local soil moisture gradients (Young 1982; Keith & Myerscough 1993), as well as regional gradients of precipitation and evapotranspiration (Young 1986; Keith et al. 2010). Thirdly, swamp-woodland boundaries shift markedly in response to variation in climatic moisture, possibly in concert with fire events, over decadal time scales (Keith et al. 2010). A range of greenhouse gas emission scenarios suggest that during the 21st century the climate within the distribution of Coastal Upland Swamps will become warmer and drier, with a greater proportion of rain falling during summer (Hennessy et al. 2004; DECC 2008b; Pitman & Perkins 2008). Regional projections also suggest an increase in the frequency of extreme fire weather, suggesting that fires may become more frequent and more intense. Under these conditions the distribution of suitable habitat for Coastal Upland Swamps is projected to contract (Keith et al. 2010) and some ecological and hydrological functions may be expected to decline. Modelling suggests that a decline of around 70% is likely in the next 50 years based on future climate scenarios (Keith pers comm. 2011). This is equivalent to a large reduction in geographic distribution. ‘Anthropogenic climate change’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

18. Subsidence and warping of the land surface associated with longwall mining of underground coal seams potentially changes hydrological processes involving both ground water and surface water. Longwall mining results in fracturing of bedrock layers between the coal seam and the surface, as well as subsidence, upsidence, tilting and buckling of the ground surface and valley closure (Department of Planning 2008). Horizontal and vertical displacements may occur up to 1-3 km outside the footprint of the mine workings (ACARP 2001, 2002) and may continue several years after seam extraction, although most movement occurs soon afterwards (Holla & Barclay 2000). There are two general mechanisms by which these movements may cause changes in the hydrology of upland swamps (Booth 2006; NSW PAC 2009): i) water drains into cracks in the bedrock that open beneath or upslope of the swamp as a result of simple tensile strains or complex buckling and shear that enhances connectivity of fractures; and ii) tilting of the surface results in re-distribution of overland flows, loss of water from swamp margins and/or concentration and channelisation of runoff. Specific hydrological impacts may include: desiccation indicated by decline of piezometric levels; reduction of baseflow discharge to streams; alteration of groundwater flow patterns; water quality changes resulting from unconfinement of confined aquifers; and leakage of upper aquifers to lower aquifers (Booth 2002, 2006, 2007; Booth et al. 1998; Madden & Merrick 2009; Madden & Ross 2009). Impacts of longwall mining on Coastal Upland Swamp are difficult to predict and detect due to non-linearities and complex dependencies on geological features and mine characteristics, time lags in hydrological and ecological responses and stochastic influences such as rainfall variation during and after subsidence. The latter can be crucial to erosion outcomes (Young 1982; Krogh 2007). Adjustment of the swamp biota to new hydrological regimes may involve considerable ecological lags and potential interactions with climatic conditions, as well as fire regimes, which govern life-cycle processes in a wide range of species. Thus changes in species composition resulting from subsidence may not be fully evident until multiple fire cycles after the completion of mining operations. The risks of subsidence impacts on swamps are related to mine layout and design characteristics, including panel width, panel height, pillar width, depth of mining operations, as well as the structure of geological strata (including faults and joints), and surface topography (Krogh 2007). The NSW Planning and Assessment Commission (2010) defined thresholds for geological strains, tilt, valley closure and relative depth of cover that should be used to identify risks of negative environmental consequences on Coastal Upland Swamp. Large swamps, those that contribute most to biodiversity and hydrological function, are likely to be more susceptible to these impacts than smaller swamps because they usually span two or more longwall panels and are consequently exposed to greater tensile and compressive strains, increasing the risk of bedrock fracture and tilting. The impacts of mine subsidence include gradual or rapid drying of swamp soils, decline of the most groundwater-dependent plant species and consequent changes in vegetation structure, decline of groundwater-dependent fauna including macro-invertebrates and stygofauna, channelisation and consequent erosion of swamp sediments, oxidation of peaty sediments resulting in increased hydrophobicity and flammability. Although a systematic regional analysis of subsidence parameters and impacts on uplands swamps is lacking, a number of examples of these subsidence impacts have been documented. These include: knickpoint formation that led to extensive gullying and collapse of Drillhole Swamp (Young 1982); reduced groundwater levels and moisture content following cracking of the impervious sandstone base rock beneath swamps 18 and 19 in the Avon catchment (Gibbins 2003); significant scouring and gullying when severe fire and intense storms followed desiccation of swamps in the Upper Avon and Cordeaux catchment areas (Krogh 2004); apparent changes in swamp bed gradients and altered flow paths associated with fracturing and tilting of bedrock beneath Flatrock Swamp in the Woronora catchment (Krogh 2004; Mills & Huuskes 2004); and bedrock fracturing followed by loss of groundwater in Dendrobium Swamp 1 in the Cordeaux catchment area (BHPBIC 2009). Krogh (2007) concluded that there is an increasing frequency of severe fracturing of surface strata, watercourses and beds of swamps as a result of longwall mining operations in the southern coalfields of New South Wales. More recent mine designs tend to involve greater panel widths, which are likely to be associated with higher subsidence impacts. Almost all Coastal Upland Swamps on the Woronora plateau are subject to existing underground mining leases (Krogh 2007). While some swamps are represented within statutory conservation reserves, these generally have depth restrictions above the coal seams that do not preclude underground mining operations. ‘Alteration of habitat following subsidence due to longwall mining’ and ‘Alteration to the natural flow regimes of rivers, streams, floodplains and wetlands’ are listed as Key Threatening Processes under the Threatened Species Conservation Act 1995.

19. Exploration and extraction of coal seam gas poses a future threat to Coastal Upland Swamp, as these activities are likely to involve many of the impacts described above for longwall mining. In addition, gas extraction may require dewatering of the coal seams and/or injection of fluids to fracture the coal seam and promote gas liberation/drainage. Sutherland et al. (2011) identified hydraulic fracturing as one of 15 emerging global threats to biodiversity. Significant environmental impacts on hydrological and ecological functions of Coastal Upland Swamp may occur if toxic injection fluids or saline/alkaline coal seam water find their way into the swamps and associated streams. Exploration of coal seam gas beneath the Woronora plateau is currently underway (e.g. Olsen Consulting Group 2009).

20. Several different fire regimes threaten the diversity of flora and fauna within Coastal Upland Swamp in the Sydney Basin bioregion. These include regimes that involve substrate fires, recurring short intervals or long intervals. Under extreme fire weather conditions the peaty substrate that accumulates in wetter parts of Coastal Upland Swamp is flammable, especially when antecedent weather conditions result in low water table levels. Combustion results in consumption of the peaty substrate and mortality of soil seedbanks and fauna, lignotubers, rhizomes and other underground organs that would otherwise survive surface and canopy fires. Substrate fires are extremely difficult to extinguish and their effects may be long-lasting as rates of sediment accumulation and peat formation are slow. Disruption of the peaty substrate and its root mat can act as nick-points for channelisation of overland and subsurface flow, resulting in extensive erosion beyond the immediate area of substrate consumption. Erosive impacts may be amplified when substrate fires are followed by intense rainfall events, resulting in the flushing of large areas of swamp sediments and vegetation from headwater valleys. Intense rainfall events are not infrequent within the distribution of Coastal Upland Swamp, and examples of substrate combustion and subsequent sediment flushing were observed in swamps on the northern Woronora plateau after severe fires were followed by intense rainfall events in summer of 2001-02 (Krogh in litt. December 2010). An increased frequency of extreme fire weather projected for south-eastern Australia in the 21st century (Lucas et al. 2007) is likely to promote the risk of more frequent and more extensive substrate fires.

21. High frequency fires threaten populations of some plant species in Coastal Upland Swamp. Among the most susceptible species are a group of serotinous obligate seeders, often structurally dominant species, (Banksia ericifolia, Hakea teretifolia, Leptospermum squarrosum, Melaleuca squamea and Petrophile pulchella) in which post-fire seedbank accumulation may be interrupted by fire recurrence resulting in population declines and local extinctions (Bradstock & O’Connell 1988) in Coastal Upland Swamp. Of these, M. squamea is already rare within the community and B. ericifolia is an important winter food source for a range of vertebrate fauna, suggesting that fire-related declines in those plants may adversely affect populations of some animals. A range of other woody species may also be susceptible to high frequency fires over longer time scales (Keith 1996). ‘High frequency fire resulting in the disruption of life cycle processes in plants and animals and loss of vegetation structure and composition’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

22. Fire regimes that include sustained recurrence of medium to long intervals between successive fires are also likely to threaten a significant component of the Coastal Upland Swamp flora. Such fire regimes promote development of dense populations of the competitive dominants of the community which, if sustained, are likely to cause declines and potential elimination of co-occurring plant species (Keith & Bradstock 1994; Keith et al. 2007). There is strong evidence from swamps in O’Hares Creek catchment during 1983-2003 that increased densities of the dominant shrubs co-incided with declines in certain understorey plants, consistent with expectations under fire regimes that were close to optimal for the dominants during that period (Keith et al. 2007). The most susceptible species were woody resprouters and some herbaceous resprouters.

23. Localised disturbance associated with unauthorised use of off-road vehicles, trail bikes and horses may cause localised erosion and weed invasion within Coastal Upland Swamp in the Sydney Basin bioregion. As discussed above, localised erosion may result in development of knick points that initiate more widespread erosion of swamp sediments, and these effects may be exacerbated by bushfires and/or intense rainfall events.

24. Coastal Upland Swamp in the Sydney Basin bioregion is not eligible to be listed as a Critically Endangered Ecological Community.

25. Coastal Upland Swamp in the Sydney Basin bioregion is eligible to be listed as an Endangered Ecological Community as, in the opinion of the Scientific Committee, it is facing a very high risk of extinction in New South Wales in the near future, as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2010:

Clause 17 Reduction in geographic distribution of ecological community

The ecological community has undergone, is observed, estimated, inferred or reasonably

suspected to have undergone or is likely to undergo within a time span appropriate to the

life cycle and habitat characteristics of its component species:

(b) a large reduction in geographic distribution,

 

Clause 18 Restricted geographic distribution of ecological community

The ecological community’s geographic distribution is estimated or inferred to be:

(b)

highly restricted,

and the nature of its distribution makes it likely that the action of a threatening process could cause it to decline or degrade in extent or ecological function over a time span appropriate to the life cycle and habitat characteristics of the ecological community’s component species.

 

Clause 19 Reduction in ecological function of ecological community

The ecological community has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time span appropriate to the life cycle and habitat characteristics of its component species:

(b)

a large reduction in ecological function,

as indicated by any of the following:

(d)

change in community structure,

(e)

change in species composition,

(f)

disruption of ecological processes,

(h)

degradation of habitat,

(i)

fragmentation of habitat.

 

 

Dr Richard Major

Chairperson

Scientific Committee

 

Proposed Gazettal date: 15/04/11

Exhibition period: 15/04/11 – 10/06/11

 

References:

 

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ACARP (2002) ‘Impacts of mine subsidence on the strata and hydrology of river valleys – Management Guidelines for undermining cliffs, gorges and river systems. Final Report C9067 Stage 2.’ Australian Coal Association Research Program, Brisbane.

 

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Page last updated: 15 April 2011