Lower Hunter Spotted Gum - Ironbark Forest in the Sydney Basin Bioregion - Determination to make minor amendment to Part 3 of Schedule 1 of the Threatened Species Conservation Act

The Scientific Committee, established under the Threatened Species Conservation Act, has made a Determination to make a minor amendment to Part 3 of Schedule 1 (Endangered ecological communities) of the Act by inserting the Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion (as described in the determination of the Scientific Committee under Division 5 Part 2) and as a consequence to omit reference to the Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion (as described in the final determination to list the ecological community) which was published on pages 420 to 426 in the NSW Government Gazette No. 26 dated 18 February 2005. Minor amendments to the Schedules are provided for by Division 5 of Part 2 of the Act.

The Scientific Committee is of the opinion that the amendment is necessary or desirable to correct a minor error in the determination by removing reference to the Dungog Local Government Area as this Area does not occur in the Sydney Basin Bioregion (Thackway & Cresswell, 1995)

The Scientific Committee has found that:

1. Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion is the name given to the ecological community that occurs principally on Permian geology in the central to lower Hunter Valley. The Permian substrates most commonly supporting the community belong to the Dalwood Group, the Maitland Group and the Greta and Tomago Coal Measures, although smaller areas of the community may also occur on the Permian Singleton and Newcastle Coal Measures and the Triassic Narrabeen Group (NSW Department of Mines 1966, 1969). The community is strongly associated with, though not restricted to, the yellow podsolic and solodic soils of the Lower Hunter soil landscapes of Aberdare, Branxton and Neath (Kovac and Lawrie 1991). These substrates are said to produce ‘moderately fertile’ soils (Kovac and Lawrie 1991). Lower Hunter Spotted Gum – Ironbark Forest is dominated by Corymbia maculata, (Spotted Gum) and  Eucalyptus fibrosa (Broad-leaved Ironbark), while  E. punctata (Grey Gum) and  E. crebra (Grey Ironbark) occur occasionally. A number of other eucalypt species occur at low frequency, but may be locally common in the community. One of these species,  E. canaliculata, intergrades extensively in the area with  E.punctata. The understorey is marked by the tall shrub,  Acacia parvipinnula, and by  the  prickly shrubs,  Daviesia ulicifolia, Bursaria spinosa, Melaleuca nodosa and  Lissanthe strigosa. Other shrubs include  Persoonia linearis, Maytenus silvestris and  Breynia oblongifolia. The ground layer is diverse; frequent species include  Cheilanthes sieberi, Cymbopogon refractus, Dianella revoluta,  Entolasia stricta, Glycine clandestina, Lepidosperma laterale, Lomandra multiflora, Microlaena stipoides, Pomax umbellata, Pratia purpurascens, Themeda australis and  Phyllanthus hirtellus (NPWS 2000, Hill 2003, Bell 2004). In an undisturbed condition the structure of the community is typically open forest. If thinning has occurred, it may take the form of woodland or a dense thicket of saplings, depending on post-disturbance regeneration.

2. Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion is characterised by the following assemblage of species:

3. The total species list of the community is considerably 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 condition and by its disturbance (including fire and logging) history. The number of species, and the above ground relative abundance of species will change with time since disturbance, and may also change in response to changes in fire regime (including changes in fire frequency). At any one time, above ground individuals of some species may be absent, but the species may be represented below ground in the 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, the community also includes micro-organisms, fungi, cryptogamic plants and a diverse fauna, both vertebrate and invertebrate. Some of these components of the community are poorly documented.

4. Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion is restricted to a range of approximately 65 km by 35 km centred on the Cessnock – Beresfield area in the Central and Lower Hunter Valley (NPWS 2000). Within this range, the community was once widespread. A fragmented core of the community still occurs between Cessnock and Beresfield. Remnants occur within the Local Government Areas of Cessnock, Maitland, Singleton, Lake Macquarie, Newcastle, and Port Stephens but may also occur elsewhere within the bioregion. Outliers are also present on the eastern escarpment of Pokolbin and Corrabare State Forests on Narrabeen Sandstone.

5. Threatened species recorded within this community include Callistemon linearifolius, Grevillea parviflora subsp.  parviflora, Persoonia pauciflora, Rutidosis heterogama, Swift Parrot  Lathamus discolor (Saunders 2002), Turquoise Parrot  Neophema pulchella, Glossy Black Cockatoo Calyptorhynchus lathami, Regent Honeyeater  Xanthomyza  phygria, Black-chinned Honeyeater  Melithreptus gularis  gularis, Brown Treecreeper  Climacteris picumnus victoriae, Powerful Owl  Ninox strenua, Koala  Phascolarctos  cinereus, Yellow-bellied Glider  Petaurus australis, Squirrel Glider  Petaurus norfolcensis (Smith and Murray 2003), Common Bentwing Bat  Miniopterus schriebersii and Eastern Freetail Bat  Mormopterus norfolkensis.

6. Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion belongs to a complex of ecological communities that were identified in an analysis of floristic data gathered in a vegetation survey of the Lower Hunter – Central Coast region (NPWS 2000). The methods of survey and analysis employed by NPWS (2000) were found to produce a reliable regional-scale overview of native vegetation in the Lower Hunter – Central Coast area, although limitations apply to fine-scale uses of the map (Nicholls et al. 2003). This analysis, and subsequent analyses based on additional floristic data from the Hunter valley floor (e.g. Hill 2003, Bell 2004, Peake unpubl. data), identified Lower Hunter Spotted Gum – Ironbark Forest as a distinct assemblage of species. Other assemblages that may include spotted gum as a dominant species, have geographically distinct distributions outside the core area where this community primarily occurs (Cessnock – Beresfield). These other assemblages include: Coastal Foothills Spotted Gum – Ironbark Forest, Seaham Spotted Gum – Ironbark Forest and Central Hunter Spotted Gum – Ironbark – Grey Box Forest (NPWS 2000). Analysis of additional data from north of the Hunter River and other parts of the Hunter valley indicates the existence of another distinct assemblage dominated by spotted gums and ironbarks on Carboniferous sediments of the footslopes of the Barrington plateau. Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion belongs to the Hunter - Macleay Dry Sclerophyll Forests vegetation class of Keith (2004).

7. Eucalyptus fibrosa,  Acacia parvipinnula and prickly shrub species occur more frequently or in greater abundance in Lower Hunter Spotted Gum – Ironbark Forest than in any of the other communities mentioned above. Around the margins of its core distribution, Lower Hunter Spotted Gum – Ironbark Forest may intergrade with other communities (e.g Hill 2003). Toward the coast and south, Lower Hunter Spotted Gum – Ironbark Forest may be replaced by Coastal Foothills Spotted Gum – Ironbark Forest, in which  Eucalyptus umbra, E. siderophloia, Syncarpia glomulifera and  Angophora costata occur more frequently, as do  Polyscias sambucifolia, Imperata cylindrica and  Pseuderanthemum variabile. Toward the north-east, Lower Hunter Spotted Gum – Ironbark Forest may be replaced by Seaham Spotted Gum – Ironbark Forest, in which  Eucalyptus crebra, E. punctata, E. acmenoides, E. moluccana and  E. siderophloia, occur more frequently, along with  Acacia falcata, A. implexa, Leucopogon  juniperinus, Aristida vagans and  Pseuderanthemum variabile. Seaham Spotted Gum – Ironbark Forest typically occurs on sediments of Carboniferous age, in contrast to the younger Permian sediments that support Lower Hunter Spotted Gum-Ironbark Forest, although the two communities intergrade where these substrates adjoin (NPWS 2000, Hill 2003). Toward the west and north-west, Lower Hunter Spotted Gum – Ironbark Forest may be replaced by Central Hunter Spotted Gum – Ironbark – Grey Box Forest, which has a higher frequency of  Eucalyptus crebra and  E. moluccana and a more open grassy understorey distinguished by herbs such as  Desmodium  varians, Glycine tabacina, Dichondra repens, Brunoniella australis and  Calotis lappulacea. On open depressions and drainage flats within the Cessnock-Beresfield area, Lower Hunter Spotted Gum – Ironbark Forest may be replaced locally by Hunter Lowlands Redgum Forest, in which  Eucalyptus tereticornis, E. punctata, E. crebra and  Angophora floribunda, occur more frequently, as do  Breynia oblongifolia, Leucopogon juniperinus, Jacksonia scoparia and  Brunoniella australis (NPWS 2000).

8. Clearing and other disturbances have resulted in a high degree of fragmentation of the community. Four large patches of Lower Hunter Spotted-Gum – Ironbark Forest are estimated to have covered nearly 50000ha prior to European settlement, representing 75% of the total distribution. The community is currently mapped as occurring in more than 4 800 fragments, of which more than 4 500 are less than 10 ha in area (House 2003). The four largest patches now cover about 7 000 ha, representing less than one-quarter of the current distribution, or about 10% of the estimated pre-European distribution (House 2003). Clearing of native vegetation is listed as a Key Threatening Process under the Threatened Species Conservation Act (1995).

9. Using recently updated mapping of extant Lower Hunter Spotted Gum – Ironbark Forest based on fine-scale aerial photograph interpretation of extant woody native vegetation, House (2003) estimated that approximately 26500 ha of the community remains with its tree canopy cover in a ‘substantially unmodified’ condition, representing approximately 40% of its pre-European distribution. However, this estimate is based on the collective canopy cover of trees (i.e. where tree canopy cover was estimated to be greater than 20%, the canopy was assumed to be ‘unmodified’ and not substantially thinned), and does not consider the growth stages of trees that contribute to the cover. Growth stage mapping is available for approximately 6000 ha of Lower Hunter Spotted Gum – Ironbark Forest on public land (RACAC 1995), of which only 3% was assessed as containing a sub-dominance of ‘overmature’ and ‘senescent’ tree crowns indicative of old growth forest. Seventy-five per cent of this area was assessed as ‘young forest’, indicating regeneration from past logging and wildfire. Some areas of Lower Hunter Spotted Gum – Ironbark Forest on private land also reflect a continuing history of degradation. In the Blackhill district, for example, much of the existing vegetation was cleared, and is now largely composed of dense stands of juvenile saplings. This regrowth has since been further affected by clearing and thinning, creation of electricity transmission easements, and ongoing grazing by goats and cattle. In addition, House (2003) estimated that there are a further 4650ha of Lower Hunter Spotted Gum – Ironbark Forest with a modified or substantially modified tree canopy cover.

10. The condition of the understorey has not been mapped systematically. There are no quantitative estimates of the area of the community that retains a substantially unmodified understorey. However, qualitative information suggests that there has been extensive disturbance to the understorey associated with logging, expansion of unplanned tracks and trails, rubbish dumping, off-road vehicle use, arson and weed invasion, even in stands that are currently within a conservation reserve (Bell 2004). These pressures are likely to intensify with the projected increases in the density of the human population within the region (Progress Economics 2004).

11. Much of the remaining Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion shows evidence of disturbance. Past logging practices and fire regimes have heavily modified some parts of the community, resulting in a simplified structure and floristics. Production areas of State Forests are actively logged at intensities specified by regulations. Frequent fires (Solanum mauritianum, wild tobacco) have degraded the more accessible remnants of the community, while transport corridors and power and communication easements have further fragmented them. As a likely consequence of continuing habitat loss and degradation, local bird observers have noted declines in species associated with spotted gum/ironbark forests, including the Swift Parrot, Regent Honeyeater, Brown Treecreeper, Black-chinned Honeyeater, Diamond Firetail, Turquoise Parrot, Fuscous Honeyeater, Eastern Shriketit and Spotted Quailthrush.

12. Clearing pressures from rural residential and residential subdivisions, industrial developments and new cropping enterprises (e.g. vineyards) continue to threaten the community particularly in Cessnock Local Government Area where the core of this community occurs. Over the past 10 years, demand for housing lots in the Lower Hunter area has nearly doubled from 1 726 in 1991-92 to 3 904 in 2003-04 (Progress Economics 2004). The ‘medium’ forecast for housing demand in Lower Hunter is 2500 lots/yr; the current supply of land zoned for housing is 12 000 lots and is projected to meet demand only for the next 5 years. Hence there are substantial pressures for rezoning land for housing within the next 10 years (Progress Economics 2004). A study of the Thornton-Killingworth sub-region projected the population to expand by 169000 people, requiring 2600 new dwellings annually over the next 25 years (Parsons Brinckerhoff 2003). Existing proposals to rezone land from rural to rural /residential around the villages of Millfield and Paxton and applications for clearing associated with rural residential and residential developments around Paxton, Bellbird, Ellalong and Mulbring will affect the ecological community. Loss of remnants of Lower Hunter Spotted Gum – Ironbark Forest will be associated with the Cessnock LEP Amendment No 60 - Hunter Economic Zone, Donaldson and Bloomfield coalmine sites at Thornton/Killingworth and F3 to Branxton National Highway link (Ecotone Ecological Consultants 1999, 2000; Connell Wagner 1997). In the Maitland Local Government Area, Hill (2003) assessed Lower Hunter Spotted Gum – Ironbark Forest as exposed to high levels of threat from development, tree dieback and grazing, and under moderate levels of threat from fragmentation, weeds, and fire.

13. Approximately 1600 hectares of Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion occurs within Werakata National Park (Bell 2004). This represents less than 2.5% of the community’s modelled pre-1750 distribution (House 2003), is distributed among several separate patches and is predominantly young regrowth forest (Bell 2004). Of an estimated 2800 ha of the community currently within State Forests, approximately 1770 ha is excluded from timber harvesting in Forest Management Zone reserves (State Forests of NSW, in litt.), although these areas may be subject to development of service easements, transport infrastructure and mineral exploration. Within the Hunter Employment Zone (HEZ), 460 ha of Lower Hunter Spotted Gum – Ironbark Forest is estimated to occur within zone 7(b) ‘Environmental Protection’. However, 7(b) zoning does not exclude development for rural properties (buildings, roads, fences, bushfire hazard reduction) and coal mining.

14. In view of the above the Scientific Committee is of the opinion that Lower Hunter Spotted Gum – Ironbark Forest in the Sydney Basin Bioregion is likely to become extinct in nature in New South Wales unless the circumstances and factors threatening its survival cease to operate, or it might already be extinct.

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal date: 05/11/10
Exhibition period: 05/11/10 - 21/01/11

References:

Bell SAJ (2004) The vegetation of Werakata National Park, Hunter Valley New South Wales. Cunninghamia 8, 331-347.

Connell Wagner (1997) ‘Fauna Impact Statement of proposed highway link F3 Freeway to Branxton.’ Roads and Traffic Authority of NSW, Sydney.

Ecotone Ecological Consultants (1999) ‘Flora and fauna investigations and planning assessment for the Tomalpin Employment Zone within the Cessnock Local Government Area.’ Cessnock City Council, Cessnock.

Ecotone Ecological Consultants (2000) ‘Additional flora and fauna investigations within the Tomalpin Employment Zone - supplementary report.’ Cessnock City Council, Cessnock.

Hill L (2003) ‘The natural vegetation of the Maitland Local Government Area.’ Maitland City Council, Maitland.

House S (2003) ‘Lower Hunter and Central Coast Regional Biodiversity Conservation Strategy, Technical Report, Digital Aerial Photo Interpretation and Updated Extant Vegetation Community Map, May 2003.’ Lower Hunter and Central Coast Regional Environmental Management Strategy, Callaghan.

Keith DA (2004) ‘Ocean shores to desert dunes: the native vegetation of New South Wales and the ACT.’ (NSW Department of Environment and Conservation: Sydney.)

Kovac M, Lawrie JW (1991) ‘Soil landscapes of the Singleton 1:250000 sheet.’ Soil Conservation Service of NSW, Sydney.

Nicholls AO, Doherty M Newsome AE (2003) ‘Evaluation of Data, Modelling Techniques and Conservation Assessment Tools for the Lower Hunter Central Coast Regional Biodiversity Conservation Strategy.’ CSIRO Sustainable Ecosystems, Canberra.

NSW Department of Mines (1966) ‘Newcastle. 1:250 000 geological sheet S1 56-2.’ NSW Government Printer, Sydney.

NSW Department of Mines (1969) ‘Singleton. 1:250 000 geological sheet S1 56-1.’ NSW Government Printer, Sydney.

National Parks and Wildlife Service (2000) ‘Vegetation Survey, Classification and Mapping: Lower Hunter and Central Coast Region.’ NSW National Parks and Wildlife Service, Sydney.

Parsons Brinckerhoff (2003) Thornton-Killingworth sub-regional conservation and development strategy. Department of Infrastructure, Planning and Natural Resources, Sydney.

Progress Economics (2004) An analysis of the projected demand and supply of land in the Lower Hunter from 2004-05 to 2013-14. A report prepared for the Urban Development Institute of Australia, Sydney.

RACAC (1995) Draft Interim Forestry Assessment. Resource and Conservation Assessment Council, Sydney. 

Saunders D (2002) ‘Assessment of Swift Parrot sites near Cessnock, Lower Hunter valley region, NSW.’ National Parks and Wildlife Service, Sydney.

Smith A, Murray M (2003) Habitat requirements of the Squirrel Glider (Petaurus norfolcensis) and associated possums and gliders on the New South Wales Central Coast.  Wildlife Research 30, 291-301.

Thackway R, Cresswell ID (1995) An interim biogeographic regionalisation for Australia: a framework for setting priorities in the National Reserve System Cooperative Program. (Version 4.0. ANCA: Canberra)