Brigalow within the Brigalow Belt South, Nandewar and Darling Riverine Plains Bioregions - Determination to make a minor amendment to Part 3 of Schedule 1 of the Threatened Species Conservation Act

The Scientific Committee, established by 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 Brigalow within the Brigalow Belt South, Nandewar and Darling Riverine Plains Bioregions (as described in the determination of the Scientific Committee under Division 5 Part 2) and as a consequence to omit reference to the Brigalow within the Brigalow Belt South, Nandewar and Darling Riverine Plains Bioregions (as described in the final determination to list the ecological community) which was published on pages 6435 to 6439 in the NSW Government Gazette No. 133 dated 23 August 2002. 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 minor errors or omissions in the Determination in relation to the Thackway and Cresswell (1995) reference.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Brigalow, where Acacia harpophylla is a dominant or co-dominant species in the canopy, is found in the Brigalow Belt South Bioregion in NSW and as isolated occurrences in the Darling Riverine Plains and Nandewar Bioregions. Bioregions are defined in Thackway and Cresswell (1995). Brigalow is usually associated with heavy clay soils.

2. Brigalow within the Brigalow Belt South, Nandewar and Darling Riverine Plains Bioregions is characterised by the following assemblage of species.

3. The total flora list for the community is considerably larger than that given above, with many species present in only one or two sites or in very small quantity. In any particular site not all of the assemblage listed above will be present. 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 bank or as dormant structures such as bulbs, corms, rhizomes, rootstock or lignotubers. The species composition of the site will be influenced by the size of the site, recent rainfall or drought conditions and by its disturbance history. The community also includes a diverse fauna, both vertebrate and invertebrate.

4. Brigalow can be found in the following structural forms. The closed canopy form of the community consists of stands of Acacia harpophylla (brigalow) found on deep gilgaied clay soils on gently undulating country, forming closed forests to 25 metres in height. The understorey is scattered and ground cover sparse.

Brigalow has a low woodland form which is typified by the dominance of Acacia harpophylla (brigalow), with pockets of vegetation dominated by  Casuarina cristata (belah) and  Eucalyptus populnea subsp . bimbil (poplar box). This variation seems to relate to site drainage characteristics, the belah favouring the less well drained sites and the poplar box favouring the better drained sites. The main canopy of this form of the community tends to be moderately dense with small trees, shrubs and grasses occurring as scattered individuals.

Remnants of Brigalow which have been subjected to some clearing or disturbance in the past may form closed shrublands with a single cohort of plants arising from root-suckers forming the canopy.

5. Brigalow in NSW has been extensively cleared for agricultural purposes and the remnants have often been thinned and modified. The original extent of the Brigalow community is not known but mapping of “Brigalow soils” in the early 1960s gives an area of potential habitat for this community in NSW of 115,300 hectares (Isbell 1962). Recent vegetation mapping of the northern wheatbelt has found that only 13,500 hectares remains of this community and that it is severely fragmented (D. Sivertsen & L. Metcalfe, pers. comm.).

6. Surviving remnants of Brigalow are often small linear patches along roadsides and the edges of paddocks where threats include ongoing logging for fence posts; road widening and invasion by weeds.

7. Brigalow ecological community is poorly represented in the existing reserve system with only one reserve, “Brigalow Park Nature Reserve”, of 202 hectares containing this community.

8. Brigalow (Acacia harpophylla dominant and co-dominant) is listed as an Endangered Ecological Community under the Commonwealth’s Environment Protection and Biodiversity Conservation Act 1999.

9. In view of the above the Scientific Committee is of the opinion that Brigalow within the Brigalow Belt South, Nandewar and Darling Riverine Plains Bioregions 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.

Dr Richard Major
Chairperson
Scientific Committee

Proposed Gazettal date: 02/12/11
Exhibition period: 02/12/11 – 03/02/12

Reference

Isbell, I. F. (1962) Soils and vegetation of the Brigalow Lands, Eastern Australia. Soils and Land Use Series No. 43. CSIRO:Melbourne.

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