Subtropical coastal floodplain forest of the NSW North Coast bioregion - endangered ecological community listing

NSW Scientific Committee - final determination

1. Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion is the name given to the ecological community associated with clay-loams and sandy loams, on periodically inundated alluvial flats, drainage lines and river terraces associated with coastal floodplains. Floodplains are level landform patterns on which there may be active erosion and aggradation by channelled and overbank stream flow with an average recurrence interval of 100 years or less (adapted from Speight 1990). Subtropical Coastal Floodplain Forest generally occurs below 50 m, but may occur on localised river flats up to 250 m elevation in the NSW North Coast bioregion. The structure of the community may vary from tall open forests to woodlands, although partial clearing may have reduced the canopy to scattered trees. Typically these forests and woodlands form mosaics with other floodplain forest communities and treeless wetlands, and often they fringe treeless floodplain lagoons or wetlands with semi-permanent standing water (e.g. Pressey 1989a).

The composition of Subtropical Coastal Floodplain Forest is primarily determined by the frequency and duration of waterlogging and the texture, nutrient and moisture content of the soil. Composition also varies with latitude. The community is characterised by the following assemblage of species:

2. The total species list of the community is considerably larger than that given above, with many species present at 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 fire, grazing, flooding and land clearing) history. The number and relative abundance of species will change with time since fire, flooding or significant rainfall, and may also change in response to changes in grazing regimes. 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.

3. Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion is known from parts of the Local Government Areas of Tweed, Byron, Lismore, Ballina, Richmond Valley, Clarence Valley, Coffs Harbour, Bellingen, Nambucca, Kempsey, Hastings, Greater Taree, Great Lakes and Port Stephens, but may occur elsewhere in this bioregion. Bioregions are defined in Thackway and Creswell (1995). Major examples once occurred on the floodplains of the Tweed, Richmond, Clarence, Macleay, Hastings and Manning Rivers, although smaller floodplains would have also supported considerable areas of this community.

4. Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion has a tall open tree layer of eucalypts, which may exceed 40 m in height, but can be considerably shorter in regrowth stands or under conditions of lower site quality. While the composition of the tree stratum varies considerably, the most widespread and abundant dominant trees include Eucalyptus tereticornis (forest red gum), E. siderophloia (grey ironbark), Corymbia intermedia (pink bloodwood) and, north of the Macleay floodplain, Lophostemon suaveolens (swamp turpentine). Other trees may be scattered throughout at low abundance or locally common at few sites, particularly where there is an influence from lithic substrates upslope. These include Eucalyptus moluccana (grey box), E. propinqua (grey gum), E. seeana (narrow-leaved red gum), Angophora subvelutina (broad-leaved apple), E. robusta (swamp mahogany), Eucalyptus resinifera subsp. hemilampra (red mahogany), E. acmenoides (white mahogany), Angophora woodsiana, A. paludosa and rainforest trees such as Ficus spp. (figs) and Cupaniopsis spp (tuckeroos). A layer of small trees may be present, including Allocasuarina torulosa (forest oak), Alphitonia excelsa (red ash), Glochidion ferdinandi (cheese tree), Callistemon spp. (bottlebrushes), Melaleuca spp. (paperbarks) and Casuarina glauca (swamp oak). Scattered shrubs include Breynia oblongifolia (coffee bush), Acacia concurrens (curracabah), Commersonia spp., and Hibiscus spp. Occasional vines include Eustrephus latifolius (wombat berry), Parsonsia straminea (common silkpod) and Geitonoplesium cymosum (scrambling lily). The groundcover is composed of abundant forbs, scramblers and grasses including Imperata cylindrica var. major (blady grass), Themeda australis (kangaroo grass), Vernonia cinerea, Dianella caerulea (blue flax lily), Pratia purpurascens (whiteroot), Cheilanthes sieberi subsp. sieberi, and Dichondra repens (kidney weed). The composition and structure of the understorey is influenced by grazing and fire history, changes to hydrology and soil salinity and other disturbance, and may have a substantial component of exotic grasses, vines and forbs.

5. Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion provides habitat for a broad range of animals, including many that are dependent on trees for food, nesting or roosting (Law et al. 2000). These include species of Cormorant (Phalacrocorax spp.) and Egret (Ardea spp. and Egrettia spp.), the Black-necked Stork (Ephippiorhynchus asiaticus), Osprey (Pandion haliaetus), Brahminy Kite (Haliastur indus), Whistling Kite (Haliastur sphenurus), White-bellied Sea-eagle (Haliaeetus leucogaster), as well as the Brush-tailed Phascogale (Phascogale tapoatafa), Squirrel Glider (Petaurus norfolcensis), Common Blossum Bat (Syconycteris australis) (Law 1994) and Grey-headed Flying Fox (Pteropus poliocephalus). The fauna of Subtropical Coastal Floodplain Forest also includes several species of southern frog (family Myobatrachidae) and tree frog (family Hylidae), such as the threatened Litoria brevipalmata, , and many species of forest birds including honeyeaters, kingfishers, cuckoos, owls, doves, whistlers and fantails.

6. Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion forms part of a complex of forested and treeless wetland communities found throughout the coastal floodplains of NSW. A recent analysis of available quadrat data from these habitats identified a distinct grouping of vegetation samples attributable to this community (Keith and Scott 2005). The combination of features that distinguish Subtropical Coastal Floodplain Forest from other endangered ecological communities on the coastal floodplains include: its dominance by a mixed eucalypt canopy, often with Lophostemon suaveolens; the presence of rainforest elements as scattered trees or understorey plants; the relatively low abundance or sub-dominance of Casuarina and Melaleuca species; the relatively low abundance of Eucalyptus robusta; and the prominent groundcover of soft-leaved forbs and grasses. It may occupy central or marginal parts of floodplains and sandy flats, including Pleistocene back-barrier flats (Pressey and Griffith 1992); habitats where flooding is periodic and soils are rich in silt and sand, sometimes humic, and show little influence of saline ground water.

7. Subtropical Coastal Floodplain Forest may adjoin or intergrade with several other endangered ecological communities, which collectively cover all remaining native vegetation on the coastal floodplains of New South Wales. These include Lowland Rainforest on Floodplain in the NSW North Coast bioregion, River-Flat Eucalypt Forest on Coastal Floodplains of the NSW North Coast, Sydney Basin and South East Corner bioregions (including the formerly listed Sydney Coastal River-flat Forest in the Sydney Basin bioregion), Swamp Sclerophyll Forest on Coastal Floodplains of the NSW North Coast, Sydney Basin and South East Corner bioregions (including the formerly listed Sydney Coastal Estuary Swamp Forest in the Sydney Basin bioregion), Swamp Oak Floodplain Forest of the NSW North Coast, Sydney Basin and South East Corner bioregions and Freshwater Wetlands on Coastal Floodplains of the NSW North Coast, Sydney Basin and South East Corner bioregions. For example, south from the Manning valley, Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion may adjoin or intergrade with River-Flat Eucalypt Forest on Coastal Floodplains of the NSW North Coast, Sydney Basin and South East Corner bioregions. As soil salinity increases Subtropical Coastal Floodplain Forest may intergrade with, and be replaced by, Swamp Oak Floodplain Forest of the NSW North Coast, Sydney Basin and South East Corner bioregions. As soils become sandier and more waterlogged, Subtropical Coastal Floodplain Forest may intergrade with, and be replaced by, Swamp Sclerophyll Forest on Coastal Floodplains of the NSW North Coast, Sydney Basin and South East Corner bioregions. The boundaries between all of these communities are dynamic and may shift in response to changes in hydrological regimes, fire regimes or land management practices The Determinations for these communities collectively encompass the full range of intermediate assemblages in transitional habitats.

8. A number of vegetation surveys and mapping studies have been conducted across the range of Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion. In the Comprehensive Regional Assessment of the north-eastern NSW (NPWS 1999), areas mapped as 'Forest Ecosystem 46, Eastern Red Gum', and those parts of areas mapped as 'Forest Ecosystem 73, Lowland Red Gum' on coastal floodplains are included within this community. On the Tweed lowlands, this community includes Eucalyptus tereticornis-E. intermedia-Lophostemon suaveolens tall to very tall open forest' (F5) of Pressey and Griffith (1992) and parts of the 'Floodplain Wetland Complex' (FL) dominated by eucalypts or Lophostemon suaveolens (Pressey and Griffith 1992). Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion is included within the 'Coastal Floodplain Wetlands' vegetation class of Keith (2002, 2004). There may be additional or unmapped occurrences of Subtropical Floodplain Forest within and beyond these surveyed areas.

9. The extent of the Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion prior to European settlement has not been mapped across its entire range. However, one estimate based on a compilation of regional vegetation maps suggests that Coastal Floodplain Wetlands, which include Subtropical Coastal Floodplain Forest, currently cover 800-1400 km2, representing less than 30% of the original extent of this broadly defined vegetation class (Keith 2004). Compared to this combined estimate, the remaining area of Subtropical Coastal Floodplain Forest is likely to be considerably smaller and is likely to represent much less than 30% of its original range. For example, there were less than 350 ha of native floodplain vegetation on the Tweed lowlands in 1985 (Pressey and Griffith 1992).

10. Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion has been extensively cleared and modified. Large areas that formerly supported this community are occupied by exotic pastures grazed by cattle, market gardens, other cropping enterprises (e.g. sorghum, corn, poplars, etc.) and, on the far north coast, canefields and tea-tree plantations. On the Tweed lowlands, Pressey and Griffith (1992) estimated that less than 3% of the original Floodplain Wetlands and Floodplain Forest remained in 1985. Similar estimates are likely to apply to Subtropical Coastal Floodplain Forest in other parts of the NSW North Coast bioregion (Goodrick 1970, Pressey 1989a, 1989b, NPWS 1999).

11. Land clearing continues to threaten Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion. Little of the remaining area occurs on public land (e.g. Pressey and Griffith 1992), with most occurring on productive agricultural land or in close proximity to rural centres. Conversion of grazing farms to cropping often involves removal of isolated paddock trees and disturbed patches of vegetation, which locally may be the only remnants of the community. The remaining stands are severely fragmented by past clearing and further threatened by continuing fragmentation and degradation, flood mitigation and drainage works, landfilling and earthworks associated with urban and industrial development, pollution from urban and agricultural runoff, weed invasion, inappropriate grazing, trampling and other soil disturbance by domestic livestock and feral animals including pigs, activation of 'acid sulfate soils' and rubbish dumping (e.g. Pressey 1989a, b; Pressey and Griffith 1992, Boulton and Brock 1999). Anthropogenic climate change may also threaten Subtropical Coastal Floodplain Forest if future flooding regimes are affected (IPCC 2001, Hughes 2003). Localised areas, particularly those within urbanised regions, may also be exposed to frequent burning which reduces the diversity of woody plant species. Clearing of native vegetation; Alteration to the natural flow regimes of rivers, streams, floodplains and wetlands; Invasion of native plant communities by exotic perennial grasses; Predation, habitat destruction, competition and disease transmission by feral pigs; Anthropogenic climate change; High frequency fire and Removal of dead wood and dead trees are listed as Key Threatening Processes under the Threatened Species Conservation Act (1995).

12. Large areas of habitat formerly occupied by Subtropical Coastal Floodplain Forest have been directly drained by construction of artificial channels (e.g. Pressey 1989a, Boulton and Brock 1999). By the early 1900s, drainage unions or trusts were formed on the major floodplains to enable adjacent landholders to arrange for co-ordinated drainage systems, which were designed and constructed by the NSW Department of Public Works. Additional areas that have not been directly drained may have been altered hydrologically by changed patterns of flooding and drainage following flood mitigation works, particularly the construction of drains, levees and floodgates (Pressey and Griffith 1992). On the north coast of NSW, expansion of Melaleuca quinquenervia and Casuarina glauca has been attributed to artificial drainage and shortening of the hydroperiod (Johnston et al. 2003). These changes appear to be closely associated with enhanced acidity, altered ionic ratios, increased dissolved organic carbon and sulfide oxidation in the soil profile (Johnston et al. 2003).

13. Very few examples of Subtropical Coastal Floodplain Forest remain unaffected by weeds. The causes of weed invasion include physical disturbance to the vegetation structure of the community, dumping of landfill rubbish and garden refuse, polluted runoff from urban and agricultural areas, construction of roads and other utilities, and grazing by domestic livestock. The principal weed species affecting Subtropical Coastal Floodplain Forest include Araujia sericiflora (moth plant), Asparagus asparagoides (bridal creeper), A. plumosus (climbing asparagus fern), Axonopus spp. (carpet grasses), Baccharis halimifolia (groundsel bush), Bidens pilosa (cobbler's peg), Cinnamonum camphora (camphor laurel), Conyza spp. (fleabanes), Hypochaeris radicata (catsear), Ipomoea spp. (morning glories), Lantana camara, Ligustrum sinense (small-leaved privet), L. lucidum (large-leaved privet), Lonicera japonica (Japanese honeysuckle), Olea europacea subsp. cuspidata (African olive), Paspalum dilatatum (paspalum), Pennisetum clandestinum (kikuyu), Rubus fruticosis agg. (blackberries), Senecio madagascariensis (fireweed), Setaria parviflora (slender pigeon grass), Sida rhombifolia (Paddy's lucerne), Solanum mauritianum (wild tobacco bush), S. nigrum (black-berry nightshade), Tradescantia fluminensis (wandering jew) and Verbena bonariensis (purpletop) (Keith and Scott 2005).

14. Small areas of Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion are contained within existing conservation reserves, including Stotts Island, Ukerebagh and Limeburners Creek Nature Reserves and Bundjalung and Myall Lakes National Parks, and these are unevenly distributed throughout the range and unlikely to represent the full diversity of the community.

15. In view of the above the Scientific Committee is of the opinion that Subtropical Coastal Floodplain Forest of the NSW North Coast bioregion is likely to become extinct in nature in New South Wales unless the circumstances and factors threatening its survival or evolutionary development cease to operate.

Associate Professor Paul Adam
Chairperson
Scientific Committee

Proposed Gazettal date: 17/12/04

Exhibition period: 17/12/04 - 28/01/05

References

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Johnston SG, Slavich PG, Hirst P (2003) Alteration of groundwater and sediment geochemistry in a sulfidic backswamp due to Melaleuca quinquenervia encroachment. Australian Journal of Soil Research 41, 1343-1367.

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