Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion - critically endangered ecological community listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Sun Valley Cabbage Gum Forest 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 Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion from Part 3 of Schedule 1 (Endangered Ecological Communities) of the Act. Listing of Critically Endangered Ecological Communities is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion is the name given to the ecological community characterised by the species assemblage listed in paragraph 2. In NSW all sites are within the Sydney Basin Bioregion (sensu Thackway & Cresswell 1995).

2. Sun Valley Cabbage Gum 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 grazing) history. The number of species, and the above ground relative abundance of species will change with time since fire, 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. These components of the community are poorly documented.

4. Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion is naturally restricted to volcanic diatremes and associated higher nutrient clay soils and is currently known to occur in the Sun Valley area, a semi-rural area of the lower Blue Mountains. Sun Valley Cabbage Gum Forest was originally a tall open forest dominated by Eucalyptus amplifolia subsp.  amplifolia (Cabbage Gum) in association with  Eucalyptus eugenioides (Thin-leaved Stringybark). Extensive clearing for timber, pastoralism and urban development has depleted, and often completely removed, the overstorey which now exists predominantly as regrowth less than approximately 30 years old with relatively few older trees. The native grassy understorey includes  Acacia parramattensis,  Imperata cylindrica,  Lomandra longifolia and  Pteridium esculentum,  although most remnant understoreys have been highly modified by grazing and disturbance. Disturbed or modified remnants are still considered to form part of the community including remnants where the vegetation, either understorey, overstorey or both, would, under appropriate management, respond to assisted natural regeneration, such as where the natural soil and associated seed bank are still at least partially intact. Other diatremes in the area support related communities but these are dominated by different canopy species, do not support  Eucalyptus amplifolia, and have less-grassy understoreys with more developed shrub layers (Benson 1992).

5. Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion includes part of Glen Forest (Map unit 6c) of Benson (1992). It has been mapped as a variant of Glen Forest (Map unit 6c) by Douglas (2001); as Eucalyptus amplifolia Tall Open-forest (sub-community 97) and map-unit 21 in derivative mapping and interpretation by BMCC (2002); and as an outlier of Burragorang River Flat Forest (FOW p31) by Tozer  et al. (2006). These maps are only indicative of the location of Sun Valley Cabbage Gum Forest and the community is not restricted to the mapped extent. Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion belongs to the Northern Hinterland Wet Sclerophyll Forests vegetation class of Keith (2004).

6. Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion has been recorded from the Blue Mountains local government area within the Sydney Basin Bioregion (sensu Thackway and Creswell 1995) and may occur elsewhere in the Bioregion. The community is not represented in any NSW National Parks and Wildlife Service estate or other conservation reserves.

7. The pre-European distribution of Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion, previously estimated at approximately 50 ha, has most recently and reliably been estimated at c. 15-20 ha, approximately 75% of which has been cleared. This equates to a large reduction in geographic distribution. Less than 5 ha of the community are extant (Douglas 2001, BMCC 2002) and this is equivalent to an extent of occurrence and an area of occupancy of 4 km² (based on 2 x 2 km grid cells, the scale of assessment recommended by IUCN 2010). A remnant of the extant community occurs on Crown land in a council-managed reserve which is largely cleared, has a high edge to area ratio, and has competing recreational uses. Other remnants occur on private land. A small remnant of the community may be present nearby in the Warrimoo area (Smith & Smith in litt. 2010). The geographic distribution is inferred to be very highly restricted.

8. Threats to Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion include clearing of native vegetation, severe fragmentation, trampling and grazing by horses and other livestock, herbicide and fertilizer application, weed invasion, limited recruitment, feral animals, altered fire regimes (particularly high frequency fire associated with bushfire mitigation and hazard reduction), climate change, and demographic and environmental stochasticity due to the restricted distribution of the community and extremely small size of remnant patches in degraded condition with high edge to area ratios. Extensive logging, grazing and clearing for housing and infrastructure has heavily depleted Eucalyptus amplifolia subsp.  amplifolia, the dominant canopy species, throughout most of the estimated pre-European distribution of the community. The majority of the community now exists as young regrowth with no known old growth or hollow-bearing individuals, and this is likely to have impacted significantly on hollow-dependent fauna. Removal of the understorey has significantly altered the community structure and resulted in the invasion of weed species which, together with grazing and fertilizer application, are limiting the recruitment of understorey plants and tree species. The vast majority of remnants with an intact overstorey no longer contain a significant native understorey and recruitment of overstorey species is negligible due to widespread livestock grazing, mowing, slashing, gardening and maintenance of cleared or modified areas on private land. Altered fire regimes and high frequency fire may be threatening remnants on private land proximal to housing. Removal of dead trees and coarse woody debris on private land for firewood and/or bushfire hazard reduction reduces the community’s habitat complexity and may exclude some fauna species. Feral and domestic animals may significantly degrade the ecological function of the community through the spread of weeds, herbivory and soil disturbance, and the predation and depletion/local extinction of native fauna. Anthropogenic climate change has the potential to threaten the community through more frequent, more intense and longer duration droughts, altered fire regimes, more frequent and/or more severe storms leading to increased soil erosion and physical damage to vegetation. ‘Clearing of native vegetation’, ‘Invasion of native plant communities by exotic perennial grasses’, ‘Invasion and establishment of exotic vines and scramblers’, ‘High frequency fire resulting in the disruption of life cycle processes in plants and animals and loss of vegetation structure and composition’, ‘Loss of hollow bearing trees’, ‘Removal of dead wood and dead trees’ and ‘Anthropogenic climate change’ are listed as Key Threatening Processes under the  Threatened Species Conservation  Act 1995. Collectively, these threats have led to changes in community structure and species composition, disruption of ecological processes, habitat degradation and fragmentation, and invasion and establishment of exotic species, indicative of a very large reduction in ecological function of the community.

9. Weed invasion is a major threat to the community, particularly at its interface with housing, roads and drainage, and on private land. Exotic species that threaten the community include:

10. Fauna species of conservation significance which may be associated with Sun Valley Cabbage Gum Forest include the Squirrel Glider, Petaurus norfolcensis (Smith and Smith 1995), and the Spotted Tailed Quoll,  Dasyurus maculatus (Sun Valley Bushcare Group 2010), both of which are listed as Vulnerable species on Schedule 2 of the  Threatened Species and Conservation Act 1995

11. Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion is currently listed as an Endangered Ecological Community on Part 3 of Schedule 1 of the Act.

12. Sun Valley Cabbage Gum Forest 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 2010.

Clause 18 Restricted geographic distribution of ecological community 

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

(a) very highly restricted,

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

Clause 19 Reduction in ecological function of ecological community 

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

(a) a very 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.

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal date: 15/4/2011
Exhibition period: 15/4/2011 - 10/6/2011

References:

Benson DH (1992) Natural vegetation of the Penrith 1:100 000 map sheet. Cunninghamia 2, 541-596.

BMCC (2002) ‘Native Vegetation Mapping in the Blue Mountains 1999-2002. Unpublished report.

Douglas SM (2001) ‘Native vegetation mapping of Areas 1 to 5 in Blue Mountains City local government area’. A report prepared for Blue Mountains City Council.

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)

IUCN (2010) ‘Guidelines for using the IUCN Red List Categories and Criteria. Version 8.0.’ (Standards and Petitions Working Group of the IUCN Species Survival Commission Biodiversity Assessments Sub-committee: Switzerland).

NSW Scientific Committee (2002) Final determination to list Sun Valley Cabbage Gum Forest in the Sydney Basin Bioregion as an endangered ecological community - accessed on 16 August 2010.

Smith P, Smith J (1995) ‘Flora and fauna study for Blue Mountains Environmental Management Plan: Areas 1 to 5.’ P & J Smith Ecological Consultants, Blaxland.

Sun Valley Bushcare Group (2010) Weeds of Blue Mountains Bushland – Sun Valley Bushcare Group (accessed on 16 August 2010)

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.)

Tozer MG, Turner K, Keith DA, Simpson C, 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, Sydney.