Cumberland Plain Woodland in the Sydney Basin Bioregion - critically endangered ecological community listing

NSW Scientific Committee - final determination

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Cumberland Plain Woodland in the Sydney Basin Bioregion as a CRITICALLY ENDANGERED ECOLOGICAL COMMUNITY in Part 2 of Schedule 1A of the Act and as a consequence, to omit reference to Cumberland Plain Woodland from Part 3 of Schedule 1 (Endangered Ecological Communities) of the Act. The listing of Critically Endangered Ecological Communities is provided for by Part 2 of the Act.

 

The Scientific Committee has found that:

 

1. Cumberland Plain Woodland was listed as an Endangered Ecological Community under the Threatened Species Conservation Act 1995 in June 1997 (NSW Scientific Committee 1997). Since this listing, a large volume of new data and analyses have become available. In addition, a nomination to change the status of Cumberland Woodland to Critically Endangered status has been received. This Determination addresses additional information now available in accordance with current listing criteria under the Threatened Species Conservation Regulation 2002.

 

2. Cumberland Plain Woodland is the name given to the ecological community in the Sydney Basin bioregion associated with clay soils derived from Wianamatta Group geology, or more rarely alluvial substrates, on the Cumberland Plain, a rainshadow area to the west of Sydney’s Central Business District. The mean annual rainfall of this area is typically in the range of 700-900 mm, and is generally lower than that received on more elevated terrain that partially surrounds the Plain. The community typically occurs on flat to undulating or hilly terrain up to about 350 m elevation but may also occur on locally steep sites and at slightly higher elevations. Cumberland Plain Woodland is characterised by the assemblage of species listed in paragraph 3 and typically comprises an open tree canopy, a near-continuous groundcover dominated by grasses and herbs, sometimes with layers of shrubs and/or small trees. Shrubs may sometimes occur in locally dense stands. Less disturbed stands of the community may have a woodland or forest structure. Small trees or saplings may dominate the community in relatively high densities after partial or total clearing, and the groundcover may be relatively sparse, especially where densities of trees or shrubs are high. The community also includes ‘derived’ native grasslands which result from removal of the woody strata from the woodlands and forests.

 

3. Cumberland Plain Woodland is characterised by the following assemblage of species:

 

Acacia implexa  Ajuga australis 
Aristida ramosaAristida vagans
Arthropodium milleflorum  Arthropodium minus
Asperula conferta Austrodanthonia caespitosa
Austrodanthonia racemosa var. racemosaAustrodanthonia tenuior
Bossiaea prostrata Bothriochloa decipiens
Bothriochloa macraBrunoniella australis
Bursaria spinosaCarex inversa
Centaurium spicatumCentella asiatica
Cheilanthes distansCheilanthes sieberi subsp. sieberi 
Chloris truncataChloris ventricosa
Chorizema parviflorumChrysocephalum apiculatum
Clematis glycinoides var. glycinoidesCommelina cyanea
Crassula sieberiana  Cymbonotus lawsonianus 
Cymbopogon refractus  Cyperus gracilis 
Daucus glochidiatusDaviesia ulicifolia
Desmodium brachypodiumDesmodium varians
Dianella longifoliaDichanthium sericeum
Dichelachne micranthaDichelachne parva
Dichondra repens

Dichopogon fimbriatus

Dichopogon strictus Digitaria diffusa 
Dillwynia sieberiDodonaea viscosa subsp. cuneata
Echinopogon caespitosus var. caespitosusEchinopogon ovatus
Einadia hastata Einadia nutans
Einadia polygonoidesEinadia trigonos
Elymus scaber var. scaber Eragrostis leptostachya
Eremophila debilisEriochloa pseudoacrotricha
Eucalyptus crebraEucalyptus eugenioides 
Eucalyptus moluccanaEucalyptus tereticornis
Euchiton sphaericusExocarpus cupressiformis
Fimbristylis dichotomaGalium migrans
Galium propinquumGeranium homeanum
Geranium solanderi var. solanderiGlossogyne tannensis
Glycine clandestina Glycine microphylla 
Glycine tabacina Goodenia hederacea subsp. hederacea
Hardenbergia violacea Hypericum gramineum
Hypoxis hygrometrica Hypoxis pratensis var. pratensis 
Indigofera australisJuncus usitatus
Lachnagrostis avenacea var. avenaceaLomandra filiformis subsp. filiformis
Lomandra multiflora subsp. multifloraMentha diemenica

Microlaena stipoides var. stipoides 

Opercularia diphylla

Oxalis perennans                            

Panicum effusum

Paspalidium distans 

Phyllanthus virgatus

Plantago debilis

Plantago gaudichaudii

Plectranthus parviflorus

Poa labillardieri var. labillardieri 

Pratia purpurascens  

Pultenaea microphylla

Rubus parvifolius  

Scleria mackaviensis

Scutellaria humilis 

Senecio diaschides 

Senecio hispidulus var. hispidulus

Sida corrugata

Solanum cinereum

Solanum prinophyllum

Sorghum leiocladum 

Sporobolus creber

Sporobolus elongatus 

Stackhousia viminea

Themeda australis 

Tricoryne elatior 

Vernonia cinerea var. cinerea 

Veronica plebeia

Wahlenbergia gracilisWahlenbergia stricta subsp. stricta

Wurmbea dioica subsp. dioica

Zornia dyctiocarpa var. dyctiocarpa 

                              

 

Other tree species occurring less frequently in this community include:

Angophora bakeri          Angophora floribunda 
Angophora subvelutina Corymbia maculata
Eucalyptus amplifolia Eucalyptus baueriana 
Eucalyptus bosistoanaEucalyptus fibrosa 
Eucalyptus globoideaEucalyptus longifolia
Eucalyptus paniculataEucalyptus punctata
Syncarpia glomulifera 

 4. 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. 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. Benson and Howell (2002) and Benson & von Richter (2008) document the temporal variability in the species composition of the community. The list of species given above is mainly of vascular plant species, however the community also includes micro-organisms, fungi, cryptogamic plants and a diverse fauna, both vertebrate and invertebrate. The mammalian and avian components of the fauna have been described by Leary (in litt. August 2007) and Farrell (in litt. June 2007). Other components of the community are poorly documented (although see Benson & von Richter 2008).

 

5. Cumberland Plain Woodland is characterised by an upper-storey that is usually dominated by Eucalyptus moluccana (Grey Box) and E. tereticornis (Forest Red Gum), often with E. crebra (Grey Ironbark), E. eugenioides (Narrow-leaved Stringybark), Corymbia maculata (Spotted Gum) or other less frequently occurring eucalypts, including Angophora floribunda, A. subvelutina (Broad-leaved Apple), E. amplifolia (Cabbage Gum) and E. fibrosa (Broad-leaved Ironbark). The community may have an open stratum of small trees that may include any of these eucalypts, as well as species such as Acacia decurrens (Black Wattle), A. parramattensis (Parramatta Wattle), A.implexa (Hickory Wattle) or Exocarpos cupressiformis (Native Cherry). Shrubs are typically scattered in the understorey but may be absent or locally dense as a result of clearing activity or changes in grazing or fire regimes. Bursaria spinosa (Blackthorn) is usually dominant, while other species include Daviesia ulicifolia (Gorse Bitter Pea), Dillwynia sieberi, Dodonaea viscosa subsp. cuneata and Indigofera australis (Native Indigo). The ground cover is dominated by a diverse range of grasses including Aristida ramosa (Purple Wiregrass), A. vagans (Threeawn Speargrass), Cymbopogon refractus (Barbed Wire Grass), Dichelachne micrantha (Plumegrass), Echinopogon caespitosus (Forest Hedgehog Grass), Eragrostis leptostachya (Paddock Lovegrass), Microlaena stipoides (Weeping Grass), Paspalidium distans and Themeda australis (Kangaroo Grass), and with graminoids Carex inversa (Knob Sedge), Cyperus gracilis, Lomandra filiformis subsp. filiformis (Wattle Mat-rush) and L. multiflorus subsp. multiflorus (Many-flowered Mat-rush). The ground cover also includes a diversity of forbs such as Asperula conferta (Common Woodruff), Brunoniella australis (Blue Trumpet), Desmodium varians (Slender Tick Trefoil), Dianella longifolia (Blue Flax Lily), Dichondra repens (Kidney Weed), Opercularia diphylla, Oxalis perennans and Wahlenbergia gracilis (Australian Bluebell), as well as scramblers, Glycine spp. and Hardenbergia violacea (Native Sarsaparilla) and the fern Cheilanthes sieberi (Poison Rock Fern).

 

6. The structure of the community varies depending on past and current disturbances, particularly clearing, fire and grazing. Contemporary tree-dominated stands of the community are largely relics or regrowth of originally taller forests and woodlands, which are likely to have had scattered shrubs and a largely continuous grassy groundcover. At some sites, mature trees may exceed 30m tall, although regrowth stands may be shorter than 10 m tall. After total or partial clearing, the tree canopy may remain sparse or may regrow to form dense stands of saplings and small trees, which are typically associated with a ground layer of reduced cover and diversity. Either or both of the upper-storey and mid-storey may be absent from the community. Native grasslands derived from clearing of the woodland and forest are also part of this community if they contain characteristic non-woody species listed in paragraph 3.

 

7. Cumberland Plain Woodland includes: ‘Shale Hills Woodland’ (map unit 9) and ‘Shale Plains Woodland’ (map unit 10) of Tozer (2003); ‘Spotted Gum Forest’ (map unit 9b), ‘Grey Box Woodland’ (map unit 10c) and ‘Grey Box – Ironbark Woodland’ (map unit 10d) of Benson (1992); and ‘Cumberland Plain Woodlands’ of Benson & Howell (1990a; b). Tindall et al. (2004) and Tozer et al. (2006) subsequently reproduced Tozer’s (2003) classification and mapping, re-labelling map units 9 and 10 as ‘Cumberland Shale Hills Woodland’ (map unit GW p28) and ‘Cumberland Shale Plains Woodland’ (map unit GW p29), respectively. Cumberland Plain Woodland belongs to the Coastal Valley Grassy Woodlands vegetation class (Keith 2004).

 

8. Several other ecological communities listed under the Threatened Species Conservation Act 1995 may intergrade with Cumberland Plain Woodland. These include Cooks River/ Castlereagh Ironbark Forest in the Sydney Basin Bioregion; Moist Shale Woodland in the Sydney Basin Bioregion; Shale / Sandstone Transition Forest; Shale Gravel Transition Forest in the Sydney Basin Bioregion; and Sydney Turpentine-Ironbark Forest. While Tozer (2003) provides information on the features that distinguish these communities, some transitional stands will be difficult to assign to a single community with a high level of confidence (Keith 2009). Transitional stands between Cumberland Plain Woodland and other communities listed under the Threatened Species Conservation Act 1995 are considered part of a listed community, and should be assigned to the community with which they share greatest resemblance in species composition and other properties.

 

9. Cumberland Plain Woodland in the Sydney Basin Bioregion is included within the critically endangered ecological community listed under the Environment Protection and Biodiversity Conservation Act as “Cumberland Plain Shale Woodlands and Shale-Gravel Transition Forest”. However the Commonwealth listing advice excludes some patches, here regarded as Cumberland Plain Woodland, on the basis of condition or structure thresholds.

 

10. The following threatened species have been recorded from Cumberland Plain Woodland:

 

Invertebrates

Cumberland Land Snail Meridolum corneovirensEndangered 

 Birds

 

Gang Gang Cockatoo  Callocephalon fimbriatum Vulnerable 
Glossy Black-CockatooCalyptorhynchus lathami  Vulnerable 
Brown Treecreeper Climacteris picumnus Vulnerable 
Painted Honeyeater Grantiella pictaVulnerable 
Swift Parrot Lathamus discolor Endangered 
Square-tailed Kite Lophoictinia isuraVulnerable

Hooded Robin (south-eastern form) 

Melanodryas cucullata cucullataVulnerable
Black-chinned Honeyeater (eastern subspecies)  Melithreptus gularis gularis Vulnerable 
Turquoise ParrotNeophema pulchellaVulnerable
Barking Owl Ninox connivensVulnerable
Powerful Owl Ninox strenuaVulnerable
Speckled WarblerPyrrholaemus sagittatusVulnerable
Diamond Firetail Stagonopleura guttataVulnerable 
Masked Owl Tyto novaehollandiae Vulnerable
Sooty Owl Tyto tenebricosaVulnerable
Regent HoneyeaterXanthomyza phrygiaEndangered

  

Mammals

Large-eared Pied Bat                          Chalinolobus dwyeri  Vulnerable 
Spotted-tail QuollDasyurus maculata Vulnerable
Eastern False Pipistrelle Falsistrellus tasmaniensis Vulnerable
Eastern Bent-wing Bat Miniopterus schreibersii Vulnerable 
Eastern Freetail BatMormopterus norfolkensisVulnerable 
Southern MyotisMyotis macropusVulnerable 
Yellow-bellied Glider Petaurus australis Vulnerable 
Squirrel GliderPetaurus norfolkensisVulnerable 
Koala Phascolarctos cinereusVulnerable 
Grey-headed Flying-fox Pteropus poliocephalusVulnerable 
Yellow-bellied Sheathtail Bat Saccolaimus flaviventris  Vulnerable 
Greater Broad-nosed Bat Scoteanax rueppelliiVulnerable

  

Plants

Downy Wattle Acacia pubescens Vulnerable
Juniper- leaved Grevillea       Grevillea juniperina subsp. juniperina  Vulnerable
Native Pear Marsdenia viridiflora subsp. viridiflora Endangered Population
Narrow-leaved GeebungPersoonia nutansEndangered
Spiked RiceflowerPimelea spicataEndangered
Matted Bush-peaPultenaea pedunculataEndangered 
Sydney Plains Greenhood Pterostylis saxicola Endangered
 

 

11. Cumberland Plain Woodland is restricted to the Sydney Basin Bioregion (sensu Thackway and Cresswell) and is currently known to occur within the local government areas of Auburn, Bankstown, Baulkham Hills, Blacktown, Camden, Campbelltown, Fairfield, Hawkesbury, Holroyd, Liverpool, Parramatta, Penrith and Wollondilly, but may occur elsewhere within the bioregion. Using map data from Tozer (2003), Cumberland Plain Woodland was estimated to occur within an extent of occurrence of 2810 km2, and an area of occupancy of just under 2 100 km2 based on 2 x 2 km grid cells, the spatial scale recommended by IUCN (2008) for assessing areas of occupancy for species.

 

12. Small areas of Cumberland Plain Woodland have been recorded from Kemps Creek, Mulgoa and Windsor Downs Nature Reserves, Scheyville National Park, and Leacock, Rouse Hill and Western Sydney Regional Parks.

 

13. Based on aerial photography flown in November 1998, Tozer (2003) estimated the total extent of woody vegetation referred to as Cumberland Plain Woodland was 11 054 (±1 564) ha (upper and lower plausible bounds, sensu Keith et al. 2009), representing 8.8 (±1.2)% of the pre-European distribution of the community. Patches of the community lacking woody vegetation are very small in extent and can be considered to be included within the plausible bounds. For that part of the community’s distribution to the east of the Hawkesbury-Nepean River, earlier mapping at coarser resolution by Benson & Howell (1990b) suggests a similar level of depletion, with an estimated 6 420 ha of ‘Cumberland Plain Woodlands’, representing 6% of the pre-European distribution east of the Hawkesbury-Nepean River. An update of Tozer’s (2003) map, based on interpretation of imagery flown in January-March 2007 shows that the extent of Cumberland Plain Woodland east of the Hawkesbury – Nepean River had declined by 442±46 ha, a reduction of 5.2±0.6% in 9 years (NSW Scientific Committee & Simpson 2008). These estimates indicate that the geographic distribution of the community has undergone a very large reduction over a time frame appropriate to the life cycle and habitat characteristics of its component species.

 

14. Some areas of Cumberland Plain Woodland subjected to a history of partial clearing and grazing have recently undergone a change in management to conserve the community. Examples include Mt Annan Botanic Garden, Scheyville National Park, Western Sydney Regional Park, Elizabeth Macarthur Agricultural Institute, Orchard Hills Defence Site and the former Australian Defence Industries site at St Marys. Experience from these areas suggests that the community is capable of some recovery, provided the soil has not been disturbed by earthworks, cultivation, fertiliser application or other means of nutrient or moisture enrichment (Benson & Howell 2002; Pellow 2003; Keith et al. 2005; J. Howell in litt. August 2007; J. Sanders in litt. January 2008). In contrast, restoration of Cumberland Plain Woodland has proved to be problematic on sites that have been exposed to such soil disturbance. At Western Sydney Regional Park, for example, Wilkins et al. (2003), Nichols (2005) and Nichols et al. (2005) studied the recovery of abandoned pastures that had been planted with more than 20 native tree and shrub species of Cumberland Plain Woodland. Over 10 years they found no evidence of convergence in species composition with nearby remnant stands of the community and the species composition of restored areas remained indistinguishable from untreated pastures. There was some evidence that restored vegetation had begun to develop more species-rich assemblages of moths and butterflies compared to untreated pastures, although after 10 years, it lacked a number of species characteristic of remnant woodland (Lomov et al. 2006). Ant communities also showed marked differences between restored and remnant vegetation although some ecological processes, such as pollination and seed dispersal, showed some evidence of development at restored sites (Lomov 2005). These results suggest that sites with a history of soil disturbance will be extremely slow to recover characteristics of Cumberland Plain Woodland, if at all, and that experimentation with alternative restoration technologies is required. As a large proportion of the former distribution of the community has either undergone similar histories of soil disturbance or are now occupied by urban development, opportunities for restoration of the community across significant areas appear limited.

 

15. The reduction in the geographic distribution of Cumberland Plain Woodland was initially due to tree-felling for timber and clearing for crops and pastures (Benson & Howell 1990a). Benson & Howell (1990b) estimated that the community had been reduced to approximately half of its pre-European extent by 1850. Following World War II, there was a marked acceleration in urban and industrial development, which continues to deplete the distribution of the community to the present day. These trends appear likely to continue into the future as the urban area continues to expand to accommodate Sydney’s increasing population, which is projected to grow by 1.0-1.1 million people during the 20 years 2007-2026 and 2.2-3.3 million during the 50 years 2007-2056 (Australian Bureau of Statistics 2008). Recent draft plans to develop growth centres in north-west and south-west Sydney, for example, identify staged release of land for residential and employment development over the next 25 years. These areas contain approximately 2000 ha (one-fifth) of the estimated remaining Cumberland Plain Woodland based on Tozer (2003), of which about two-thirds will be available for development, the loss of which is planned for offsetting through voluntary land acquisition and/or the establishment of conservation agreements on lands outside the Growth Centres (Growth Centres Commission 2007) for the primary purpose of biodiversity conservation. While important examples of Cumberland Plain Woodland are represented within conservation reserves, much of the remaining area of the community occurs on private land or on public easements, where it is at risk from small-scale clearing associated with housing, industrial development and transport infrastructure. There are significant logistic and technological constraints and time lags associated with efforts to restore the community (Wilkins et al. 2003; Nichols 2005; Nichols et al. 2005). ‘Clearing of native vegetation’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

 

16. Fragmentation of habitat associated with clearing has resulted in a very large reduction in the ecological function of Cumberland Plain Woodland. The remaining area of the community is severely fragmented, with more than half of the remaining tree cover mapped by Tozer (2003) occurring in patches of less than 80 ha and half of all mapped patches being smaller than 3 ha (Tozer in litt. October 2007). The integrity and survival of small, isolated stands is impaired by the small population size of many species, enhanced risks from environmental stochasticity, disruption to pollination and dispersal of fruits or seeds, and likely reductions in the genetic diversity of isolated populations (Young et al. 1996; Young & Clarke 2000). The impacts of fragmentation and associated processes are most evident in the loss of vertebrate fauna from the community (Farrell 2005; Farrell in litt. June 2007; Leary 2005; in litt, August 2007). As well, some invertebrate species, such as the Endangered Cumberland Land Snail, appear to be in decline, at least in the smaller fragments (M. Shea in litt. June 2007). The dieback of eucalypt canopies observed in stands of Cumberland Plain Woodland at Scheyville (D. Keith pers. comm. October 2008) may be a result of complex interactions involving insect attack, weed invasion, nutrient enrichment and drought, in which fragmentation also plays a role (Reid & Landsberg 2000; Wardell-Johnson et al. 2006). Despite their history of fragmentation, some very small and apparently degraded remnants may contain a surprisingly high diversity of species and important examples of rare species, particularly plants (James et al. 1999; Benson & Keith 1984; McBarron et al. 1988; Benson & Howell 1990a; Kirkpatrick & Gilfedder 1995). However, clearing and continuing degradation of these patches reduces the likelihood that all of these species will persist, particularly because a large proportion of species are known from very few locations which are not clustered in predictable ways (Benson & Howell 2002; Tozer 2003). Fragmentation also results in reduced fire frequencies within some patches, which may reduce the viability of some native plant populations, and hence the diversity of species within the patches (Clarke 2000; Watson 2005).

 

17. Changes in structure contribute to a very large reduction in the ecological function of Cumberland Plain Woodland. Almost all of the remaining area of the community is regrowth forest and woodland from past clearing activities (Benson & Howell 1990a). Mean tree densities in contemporary stands of the community were found to be substantially higher than historical estimates and tree sizes were thought to be smaller (Benson 1992). Large trees approximating the stature of the community prior to European settlement occur very sparsely within remnant patches of vegetation or remain as isolated individuals within paddocks or urban areas. Scheyville National Park, for example, which contains a large remnant of Cumberland Plain Woodland, was extensively logged and partially cleared over many decades prior to its reservation and is thought to contain as few as five large old trees likely to date from pre-European times (J. Sanders, in litt. January 2008). Loss of these large trees, which provide habitat resources for a range of fauna, is associated with declines and local extinctions of numerous birds and mammals that were once more common on the Cumberland Plain (Farrell 2005; T. Leary in litt. August 2007). Changes in understorey are difficult to assess, as responses to anthropogenic disturbances are confounded with responses to climatic variability (Benson & Howell 2002). Nevertheless, other structural changes to the community include the removal of fallen woody debris and standing dead trees, the removal of woody understorey plants, or conversely the development of regrowth stands with very high densities of eucalypt saplings or shrubs, notably Bursaria spinosa, which may suppress the ground flora. Botanist Allan Cunningham noted high densities of B. spinosa in farmland near Liverpool as early as 1817 (Lee 1927; Benson 1992), while similar phases of high shrub abundance have been observed recently at Mt Annan and Scheyville in response to abandonment of farming practices (Benson & Howell 2002; J. Sanders, in litt. January 2008). Some areas of the community now devoid of woody plant species may retain a substantial suite of native grasses and herbs in the ground layer. The Orchard Hills Defence Site includes outstanding examples of this phenomenon (Pellow 2003; Keith et al. 2005). ‘Loss of hollow-bearing trees’ and ‘Removal of dead wood and dead trees’ are listed as Key Threatening Processes under the Threatened Species Conservation Act 1995.

 

18. While a sample of the original fauna of Cumberland Plain Woodland persists, some components have already been lost and others continue to decline (Leary 2005; in litt. Aug. 2008). The original mammal fauna of the Cumberland Plain was estimated to include approximately 60 species (NPWS 1997), of which less than 40 were detected in recent intensive surveys and only 14 species are now considered to be relatively common and widespread (Leary 2005; in litt. August 2008). The majority of these latter species are micro-bats, while small ground-dwelling mammals are unexpectedly scarce. A systematic survey involving 22 000 trap nights and 14 000 hair tube nights across conservation reserves containing Cumberland Plain Woodland failed to detect any native rodents or dasyurids, except at sites on the periphery of the plain, close to larger vegetated areas on sandstone (Leary 2005; in litt. August 2008). Long-nosed Bandicoots have recently been recorded in inner western Sydney (NSW Scientific Committee 2008), but remain scarce and have not been recorded during the systematic fauna surveys of Cumberland Plain Woodland. A number of bird species have also disappeared from or markedly declined on the Cumberland Plain (Keast 1995; Farrell 2005; Leary 2005; in litt. August 2008). A sequence of repeated surveys in Scheyville National Park, the largest remnant of Cumberland Plain Woodland, have documented disappearance of the Black-chinned Honeyeater, Brown Treecreeper, Diamond Firetail, Zebra Finch, Hooded Robin, Red-capped Robin, Scarlet Robin, Flame Robin and Black-eared Cuckoo, while declines have been observed in populations of the Speckled Warbler, Fuscous Honeyeater, Jacky Winter, Weebill and Buff-rumped Thornbill (Farrell 2005; in litt. June 2008). Repeated surveys of Nurragingy Reserve near Blacktown indicate that all of these species have also been lost from the reserve, except for the Fuscous Honeyeater and Weebill (Farrell 2005; in litt. June 2008). Many of these species either feed or nest on or near the ground. Declines of reptiles and amphibians on the Cumberland Plain have been less well documented, but include at least three species of frog, one species of turtle, one skink, possibly two species of goanna and one species of snake (Leary 2005; in litt. August 2008). Two species of plants, Swainsona monticola and Thesium australe, are presumed to have gone extinct in Cumberland Plain Woodland (Benson & Howell 2002), while James et al. (1999) list many other species that have undergone substantial declines, including threatened species such as Acacia pubescens, Pimelea spicata and Pterostylis saxicola. In addition to these losses and declines across a wide range of biota within the community, Benson & Howell (1990a; 2002) describe other changes in species composition that indicate a very large reduction in the ecological function of Cumberland Plain Woodland.

 

19. Weed invasion also poses a major threat to Cumberland Plain Woodland. While very large numbers of weed species have invaded many different areas of the community, principal weed species include (Benson 1992; Tozer 2003; Benson & von Richter 2008):

Anagallis arvensis Scarlet Pimpernel 
Araujia sercifloraMoth Vine
Asparagus asparagoidesBridal Creeper
Aster subulatusWild Aster, Bushy Starwort
Centaurium tenuiflorum 
Chloris gayanaRhodes Grass
Cyclospermum leptophyllumSlender Celery
Cirsium vulgareThistle 
Conyza sumatrensis Tall Fleabane
Ehrharta erectaPanic Veldtgrass
Eragrostis curvulaAfrican Lovegrass
Heliotropium amplexicaule Blue Heliotrope 
Hypochaeris radicataCatsear
Lantana camara Lantana 
Leontodon taraxacoides subsp. taraxacoides       Lesser Hawkbit, Hairy Hawkbit
Ligustrum sinense Small-leaf Privet
Nassella neesiana Chilean Needlegrass
Olea europaea subsp. cuspidataAfrican Olive
Paspalum dilatatumPaspalum
Plantago lanceolataLamb’s Tongues, Plantain
Richardia stellaris 
Senecio madagascariensis Fireweed
Setaria gracilis Slender Pigeon Grass 
Sida rhombifoliaPaddy’s Lucerne
Solanum spp. Nightshades
Sonchus oleraceusCommon Sowthistle
Sporobolus africanus Parramatta Grass
  

  

Several of these species, particularly grasses, form a dense ground layer capable of smothering indigenous plants, reducing both reproduction and survival, and inhibiting emergence and establishment of their seedlings. The propagules of weeds are spread into Cumberland Plain Woodland by stormwater, dumping of refuse, frugivorous birds and wind (Benson & Howell 1990b), making it difficult to abate the invasion process, especially for those species capable of establishing in sites that have been exposed to relatively little disturbance (J. Sanders, in litt. January 2008). Hill et al. (2005) found that high species richness and abundance of weeds was associated with remnants that either had a history of clearing and grazing, were in close proximity to creeks or downslope from sealed roads. They also found some relationship between weeds and elevated total soil phosphorus, conductivity and water retention capacity, but relationships with these soil properties were weak and varied between sites with different types of disturbance history. The dramatic recent expansion of African Olive poses the greatest invasive threat to Cumberland Plain Woodland. Initially introduced to south-western Sydney in the 1820s, it was generally confined to the Camden-Picton area until the 1970s and now occurs frequently throughout the distribution of the community (Tozer 2003; Cuneo & Leishman 2006). Roberts (1999) mapped approximately 1000 ha of Cumberland Plain Woodland (c. 10% of total remaining) which had a dense understorey of African Olive that was visible on aerial photographs flown in November 1997. Tozer (2003) recorded African Olive in 43% of 198 plots surveyed throughout the distribution of Cumberland Plain Woodland. Cuneo et al. (2009) found that 837 ha of Cumberland Plain Woodland in south-west Sydney was invaded by African Olive (8.5% of the area assessed). The species is highly fecund, with fleshy fruit spread widely by a range of frugivorous birds, and seedlings establish readily in relatively undisturbed bushland, as well as fragmented edges (Cuneo & Leishman 2006). As shrubs grow, their canopies cast deep shade and suppress and ultimately eliminate most native shrub and groundcover species. Cook et al. (2005) and Tozer (in litt. October 2007, based on data from Tozer 2003), both recorded strong inverse relationships between the cover abundance of African Olive and the diversity and cover of native ground layer species. Other weeds that pose future threats to the community include Ailanthus altissima, Asparagus asparagoides, Acer negundo, Gleditsia triacanthos and Macfadyena unguis-cati (Benson & Howell 2002; J. Howell in litt. August 2007; J. Sanders in litt. January 2008; L. Harrold pers comm. 2009). The invasion and establishment of exotic weeds is resulting in a very large reduction in the ecological function of Cumberland Plain Woodland. ‘Invasion of exotic perennial grasses’ and ‘Invasion and establishment of exotic vines and scramblers’ are listed as Key Threatening Processes under the Threatened Species Conservation Act 1995.

 

20. Moderate to heavy grazing of Cumberland Plain Woodland by livestock and rabbits results in the decline and disappearance of palatable plant species, including shrubs and herbs, and compaction and erosion of topsoil, making re-establishment of a diverse native understorey problematic. The effects of such overgrazing may be exacerbated under drought conditions. Habitat degradation associated with overgrazing and erosion contributes to a large reduction in ecological function of the community.

 

21. The soils of Cumberland Plain Woodland have undergone chemical and structural modification associated with agricultural land uses. Trampling by livestock has resulted in localised areas of soil compaction, primarily around watering points. Research carried out at the University of Western Sydney found that mean soil inorganic nitrogen levels were two to three times higher in areas of former agricultural land use than in remnant woodland, but was unable to detect differences in other soil properties (E. C. Morris in litt. June 2007). Addition of carbon and burning reduced soil inorganic nitrogen and reduced growth of exotic ground layer species relative to native species, suggesting that elevated soil inorganic nitrogen could favour exotics to the detriment of natives in Cumberland Plain Woodland (E. C. Morris in litt. June 2007). Hill et al. (2005) found elevated levels of phosphorus and conductivity in former agricultural areas compared to remnant woodland, but did not examine soil nitrogen. The sources of nutrient addition to soils of Cumberland Plain Woodland include addition of fertilisers during previous agricultural land use, deposition of livestock dung, rubbish dumping and stormwater runoff from urban areas. Expansion of urban land uses across the Cumberland Plain is likely to increase urban runoff from sealed surfaces into remaining bushland fragments, resulting in further nutrient enrichment of soils and associated replacement of native flora by exotic species. Disruption of ecological processes and degradation of habitat associated with nutrient enrichment contributes to a very large reduction in ecological function of the community.

 

22. Fire regimes influence the plant species composition and vegetation structure of Cumberland Plain Woodland (Benson & Howell 2002; Watson 2005) and are also likely to influence other components of the biota. Based on a study of Cumberland Plain Woodland remnants with varying fire histories, Watson (2005) found that variable intervals of 4 - 12 years between successive fires are likely to maintain populations of most understorey species in the community, including resprouting and obligate-seeding shrubs, grasses and herbs. Fragmentation of Cumberland Plain Woodland may exclude fire from some patches for extended periods by reducing fire spread. The consequent reduction in fire frequency sometimes leads to increased dominance of shrubs and associated declines in diversity of grasses and herbs (Watson 2005), as well as increased abundance of woody exotic species, such as African Olive (Benson & Howell 2002; Watson 2005; von Richter et al. 2005), which is likely to further reduce the flammability of the community. Conversely, high frequencies of fires may result where fragmentation increases the interface between urban areas and bushland, as this results in increased arson, car dumping, planned fuel-reduction fires and accidental ignitions. High fire frequencies are associated with reduced diversity of native plant species in Cumberland Plain Woodland (Watson 2005). ‘High frequency fire resulting in 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. The season of fire, which may be altered as a consequence of hazard reduction fires, may also influence the species composition of the grassy woodland understorey (Knox & Clarke 2006; Benson & von Richter 2008). Disruption of ecological processes associated with alteration of fire regimes contributes to a very large reduction in ecological function of the community.

 

23. Cumberland Plain Woodland in the Sydney Basin Bioregion is eligible to be listed as a Critically Endangered Ecological Community as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future, as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:

 

Clause 25

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:

(a) a very large reduction in geographic distribution.

 

Clause 27

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:

(a) a very large reduction in ecological function,

as indicated by any of the following:

(d) a change in community structure

(e) a change in species composition

(f) disruption of ecological processes

(g) invasion and establishment of exotic species

(h) degradation of habitat

(i) fragmentation of habitat.

 

 

Dr Richard Major

Chairperson

Scientific Committee

 

Proposed Gazettal date: 18/12/09

Exhibition period: 18/12/09 – 05/03/10

 

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