Tableland Basalt Forest in the Sydney Basin and South Eastern Highlands Bioregions - endangered ecological community listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list Tableland Basalt Forest in the Sydney Basin and South Eastern Highlands Bioregions, as an ENDANGERED ECOLOGICAL COMMUNITY in Part 3 of Schedule 1 of the Act. Listing of endangered ecological communities is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Tableland Basalt Forest in the Sydney Basin and South Eastern Highlands Bioregions is the name given to the ecological community found on plateaus and tablelands with loam or clay soils derived primarily from basalt, but may also be derived from mudstones, granites, alluvium and other substrates. The community typically has an open canopy of eucalypts with sparse shrubs and a dense groundcover of herbs and grass, although disturbed stands may lack either or both of the woody strata. The community therefore includes 'derived' native grasslands which result from removal of the woody components from the woodland and forest forms of the community.

2. Tableland Basalt Forest in the Sydney Basin and South Eastern Highlands Bioregions 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) history.  The number of species, and the above ground relative abundance of species, will change with time since fire, and may also change in variation 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.  These components of the community are poorly documented.

4. Tableland Basalt Forest is dominated by an open eucalypt canopy of variable composition. Eucalyptus viminalis (Ribbon Gum) , E. radiata (Narrow-leaved Peppermint) , E.  dalrympleana subsp.  dalrympleana (Mountain Gum) and  E. pauciflora (White Sally) may occur in the community in pure stands or in varying combinations. Small trees of  Acacia melanoxylon may be scattered amongst the eucalypts. When present, a sparse layer of shrubs may include  Acacia melanoxylon (Blackwood) , A. dealbata (Silver Wattle) or  Rubus parvifolius (Native Raspberry) . The typically dense groundcover comprises a range of native grasses including  Microlaena stipoides (Weeping Grass) , Echinopogon ovatus (Hedgehog Grass) , Austrodanthonia racemosa (Wallaby Grass) , Austrostipa rudis, Poa labillardieri, P. sieberiana and Themeda australis (Kangaroo Grass), forbs including  Stellaria pungens, Dichondra spp. (Kidney weeds),  Acaena novae-zelandiae (Bidgee-widgee) , Geranium solanderi var . solanderi (Native Geranium) , Hydrocotyle laxiflora (Stinking Pennywort) , Asperula conferta (Common Woodruff) , Plantago varia (Variable Plantain) , Viola betonicifolia (Mountain Violet) , and the fern  Pteridium esculentum (Bracken) . Undisturbed stands of the community may have either a woodland or forest structure. The structure of the community varies depending on past and current disturbances, particularly clearing 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 30 m 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 tree and shrub strata may be absent from the community, as a consequence of past disturbance. 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 2.

5. Tableland Basalt Forest typically occurs on loam or clay soils associated with basalt or, less commonly, alluvium, fine-grained sedimentary rocks, granites and similar substrates that produce relatively fertile soils. Its distribution spans altitudes from approximately 600 m to 900 m above sea level, usually on undulating or hilly terrain. Mean annual rainfall varies from approximately 750 mm up to 1100 mm across the distribution of the community. Tableland Basalt Forest is currently known from the local government areas (LGA) of Bathurst Regional, Goulburn Mulwaree, Oberon, Palerang, Shoalhaven, Upper Lachlan and Wingecarribee but may occur elsewhere within the designated bioregions.

6. Tableland Basalt Forest includes the community of the same name (map unit 20) described and mapped by Tindall et al. (2004) and Tozer  et al. (2006). A survey of the Wingecarribee LGA (Eco Logical 2002) was not sufficiently detailed to discriminate this community from other types of vegetation in the region. These studies map the majority of the community, but they do not cover its most western occurrences or occurrences in the Oberon district. In the upper catchment of the Lachlan River, western occurrences of Tableland Basalt Forest include 'High altitude gum tall open-forest on fertile soils of the central tablelands' (broad vegetation type 45) of DEC (2006). The community is not clearly identifiable in the classification and map of Thomas  et al. (2000) and Gellie (2005). However, examples of the community are included within 'Eastern Tableland Dry Shrub/Grass Forest' (Forest Ecosystem 73) and 'Southern Tablelands Dry Shrub/Grass/Herb Forest' (Forest Ecosystem 74), where these units of Thomas  et al. (2000) and Gellie (2005) occur on basalt or similarly fertile substrates. None of the above studies map areas of derived native grasslands, which are part of this community (see paragraph 4). These are structural forms of the community from which the woody components of the vegetation have been lost. Tableland Basalt Forest belongs to the Tableland Clay Grassy Woodlands vegetation class of Keith (2004).

7. The species composition of Tableland Basalt Forest varies with average annual rainfall. On basalt or plutonic substrates east of Mittagong and Moss Vale, at the eastern edge of its distribution where average rainfall exceeds 1000-1100 mm per year, the community is replaced by Robertson Basalt Tall Open-forest and Mount Gibraltar Forest.  Both of these are listed as Endangered Ecological Communities under the Threatened Species Conservation Act 1995, and both are included within Southern Highlands Basalt Forest (map unit WSF p266) of Tindall et al. (2004) and Tozer  et al. (2006). They differ from Tableland Basalt Forest in having a greater frequency of  Eucalyptus fastigata and  E. cypellocarpa in the tree canopy and in having a greater frequency of mesophyllous shrubs, vines and ferns in the understorey.

8. Since European settlement and relative to the longevity of its dominant trees, which live for several hundred years, Tableland Basalt Forest has undergone a large reduction in geographic distribution. This reduction has occurred as a result of clearing vegetation from flat terrain with fertile soils for pasture development and cropping (Keith 2004, Tindall et al. 2004, Tozer  et al. 2006). The total remaining area of Tableland Basalt Forest is estimated to be less than 15 000 ha, including approximately 10 700 ha mapped in the Sydney – South Coast region by Tindall  et al. (2004) and Tozer  et al. (2006). The area of the community remaining in the Sydney – South Coast region is estimated to represent approximately 5-20% of its projected occurrence there at the time of European settlement, of which approximately 280 ha (et al. 2006). Almost all of the remaining area of the community occurs on private land or on public easements, where its geographic distribution is undergoing a continuing decline due to small-scale clearing. 'Clearing of native vegetation' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

9. Extensive clearing of Tableland Basalt Forest has resulted in fragmentation and loss of ecological connectivity.  The remaining area of the community is severely fragmented, with more than 70% of mapped extant patches estimated to be less than 10 ha (map data from Tozer et al. 2006). Many of these remaining patches occur on road reserves, the edges of house paddocks, or beside steep slopes on the edges of cleared land. Small-scale clearing associated with rural subdivisions, easements, transport corridors and other localised development continues to threaten the community. 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 and Clarke 2000). Fragmentation also results in reduced fire frequencies within some patches, which may reduce the viability of some native plant populations (Clarke 2000). Fragmentation of habitat and disruption of these ecological processes contribute to a large reduction in the ecological function of the community.

10. Much of the remaining area of Tableland Basalt Forest is regrowth forest and woodland from past clearing activities. Areas of the community that are now devoid of woody plant species have undergone more extreme structural changes, but some may retain a substantial suite of native grasses and herbs in the ground layer. Tall trees are often absent from patches of regrowth vegetation, but may remain as isolated individuals within paddocks. These and other remnant and regrowth trees may suffer episodes of elevated mortality related to drought and recurring insect attack consistent with rural tree decline (Reid and Landsberg 2000). Changes in structure and species composition of the community, including loss of large trees, which provide habitat resources for a range of fauna, contribute to a large reduction in ecological function of the community. 'Loss of hollow-bearing trees' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

11. Moderate to heavy grazing of Tableland Basalt Forest, 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 it difficult for a diverse native understorey to re-establish at times when total grazing pressure is reduced. 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. 'Competition and grazing by the feral European Rabbit, Orytolagus cuniculus (L.)' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

12. Weed invasion also poses a significant threat to Tableland Basalt Forest. Principal weed species include:

Several of these exotic species, particularly grasses, form a dense ground layer capable of smothering indigenous plants, reducing their reproduction and survival. The invasion and establishment of exotic species in Tableland Basalt Forest, results in a large reduction in the ecological function of the community. 'Invasion of native plant communities by exotic perennial grasses' is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.

13. Tableland Basalt Forest in the Sydney Basin and South Eastern Highlands Bioregions is not eligible to be listed as a critically endangered ecological community

14. Tableland Basalt Forest in the Sydney Basin and South Eastern Highlands Bioregions 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 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:

(b) a large reduction in geographic distribution.

Clause 26

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 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 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
(g) invasion and establishment of exotic species
(h) degradation of habitat
(i) fragmentation of habitat

Professor Lesley Hughes
Chairperson
Scientific Committee

Proposed Gazettal date: 04/01/08
Exhibition period: 04/01/08 – 29/02/08

References:

Clarke PJ (2000) Plant population processes in temperate woodlands in eastern Australia – premises for management. Pp 248-270 in (Eds. R J Hobbs and C J Yates) Temperate eucalypt woodlands in Australia: biology, conservation, management and restoration (Surrey Beatty & Sons: Chipping Norton).

DEC (2006) Reconstructed and extant distribution of native vegetation in the Central West Catchment. NSW Department of Environment and Conservation: Dubbo.

Eco Logical Australia (2002) Wingecarribee Biodiversity Study – vegetation mapping, threatened species, corridors and conservation assessement. Report to Wingecarribee Shire Council.

Gellie NJH (2005) Native vegetation of the southern forests: South-east Highlands, Australian Alps, South-west Slopes and South-east Corner bioregions. Cunninghamia 9, 219-254.

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).

Reid N, Landsberg J (2000) Tree decline in agricultural landscapes: what we stand to lose. Pp 127-166 in (Eds. RJ Hobbs, CJ Yates) Temperate eucalypt woodlands in Australia: biology, conservation, management and restoration (Surrey Beatty & Sons: Chipping Norton).

Thomas V, Gellie N, Harrison T (2000) Forest Ecosystem Classification and Mapping for the Southern CRA Region. Report for the NSW CRA/RFA Steering Committee, Project No. NS 08EH. NSW National Parks and Wildlife Service, Queanbeyan.

Tindall D, Pennay C, Tozer MG, Turner K, Keith DA (2004) Native vegetation map report series. No. 4. Araluen, Batemans Bay, Braidwood, Burragorang, Goulburn, Jervis Bay, Katoomba, Kiama, Moss Vale, Penrith, Port Hacking, Sydney, Taralga, Ulladulla, Wollongong. NSW Department of Environment and Conservation and NSW Department of Infrastructure, Planning and Natural Resources, Sydney.

Tozer MG, Turner K, Simpson C, Keith DA, Beukers P, MacKenzie B, Tindall D, Pennay C (2006) Native vegetation of southeast NSW: a revised classification and map for the coast and eastern tablelands. Version 1.0 NSW Department of Environment and Conservation and NSW Department of Natural Resources, Hurstvile.

Young A, Boyle T, Brown A (1996) The population genetic consequences of habitat fragmentation for plants. Trends in Ecology and Evolution 11, 413-418.

Young A, Clarke G (2000) Genetics, demography and the viability of fragmented populations. (Cambridge University Press: Cambridge).