Brigalow

Brigalow is the name given to the threatened ecological community Brigalow (Acacia harpophylla dominant and co-dominant). This community occurs on clay soils across the Border Rivers and Gwydir catchments and is characterised by an overstorey dominated by Brigalow or with Brigalow as a co-dominant with other species such as Belah (Casuarina cristata) or Bimble box (Eucalyptus populnea).

Unfortunately, large areas of this community have been cleared across our catchment and remaining fragments are listed as endangered. Several threatened flora and fauna species use Brigalow as habitat.

Brigalow is listed as a threatened ecological community under both the Australian Government's Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and the NSW Threatened Species Conservation Act 1995 (TSC Act). Activities which affect the condition or extent of Brigalow may require consent or approval.

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Where does the community occur?

In the Border Rivers-Gwydir catchment, it occurs mainly on the eastern edge of the Plains, north from Narrabri to the Queensland border. Large stands occur around Bellata, Biniguy and Croppa Creek. The largest remaining stands of Brigalow are in south-east Qld.

Specifically, Brigalow occurs within the following IBRA sub-regions of the Border Rivers and Gwydir catchments: Northern Basalts, Peel, Northern Outwash, Kaputar and Castlereagh-Barwon (www.environment.gov.au/parks/nrs/science/pubs/subregions.pdf).

Identification

Brigalow structure ranges from open woodland to forest, with a canopy dominated by, or including, Brigalow trees (Acacia harpophylla). The height of Brigalow will vary from 9-25 m depending on mean annual rainfall.

Brigalow usually has an understorey with a high diversity of shrub species and a sparse ground layer. In lower rainfall areas, with more widely spaced trees there will be a denser ground layer of grasses, chenopods and herbs. Mistletoe (particularly Amyema quandang) is a common and important component of Brigalow communities.

Species commonly occurring as a co-dominant with Brigalow in the Border Rivers and Gwydir catchments include: Eucalyptus populnea (Bimble box), E. pilligaensis (Pilliga box) and Casuarina cristata (Belah).

Brigalow is associated with gilgaied, heavy cracking clay or clay-loam soils.

Brigalow trees will vigorously resprout from root suckers if the above-ground parts are removed or damaged. The community can include dense stands of regrowth with a developing canopy.

Where it is mainly found

Brigalow is found on public and private land, usually on deep alluvial, gilgaied clay soils.  The community is usually found on plains, alluvial floodplains or low rises.

What is not Brigalow?

For Brigalow patches to fit the definition of the community protected under the EPBC Act, they must be larger than 0.5 ha and have less than 50% exotic perennial groundcover. Not all vegetation communities with Acacia harpophylla are the Brigalow ecological community. This species also occurs in Semi-evergreen Vine Thicket and Weeping Myall Woodland, which are both threatened ecological communities.

Threats

Brigalow communities are threatened with extinction or continued decline from both historical and current sources. The area of Brigalow has declined by more than 90% since European settlement, primarily due to clearing for cropping.

Clearing – illegal and legal clearing for fence lines and routine agricultural activities is a significant threat in NSW. It increases the fragmentation of Brigalow and the impact of other threats such as fire, grazing and weeds.

Fire – fire can kill above-ground parts, leaving roots to sucker, with subsequent loss of habitat and delays in flowering and setting seed.

Weeds – invasive pasture grasses such as Buffel grass (Cenchrus ciliaris), Green panic (Panicum maximus var megathyrsus) and Rhode's grass (Chloris gayana) pose a significant threat to Brigalow by displacing understorey species, preventing regeneration of trees and shrubs, and increasing the frequency and intensity of fire. Mother-of-millions (Kalanchoe tubiflora) and other succulent weeds can also invade stands and compete with native plants.

Animal damage – domestic, feral and native animals threaten Brigalow by grazing and trampling plants. Grazing eliminates many plant species and allows weeds to colonise more easily. Trampling and animal movement reduces the amount of leaf litter which is essential habitat for reptile and invertebrate species.

Infrequent seed production – natural regeneration of Brigalow trees is rare. Rare seed set events need to be followed by high summer rainfall.

Climate change – is likely to affect distribution and composition of Brigalow communities and increase the impact of other threats, particularly fire and weeds.

Management

The main priority is to maintain or increase the extent and condition of the community. This can be achieved by the following actions.

  • It is recommended that you do not clear Brigalow stands, even under permissible exemptions from the Native Vegetation Conservation Act.
  • Provide long-term protection for Brigalow through Management Agreements with the Border Rivers-Gwydir CMA or Conservation Agreements with the Office of Environment and Heritage or the Nature Conservation Trust.
  • Establish a weed-free buffer around existing stands to encourage regeneration of native species from the Brigalow community.
  • Control weeds within and near existing stands before they spread. Repeated treatments may be needed.
  • Re-establish Brigalow communities through revegetation on sites where it previously occurred. Revegetation should aim to reconnect fragmented stands of Brigalow or to expand the size of existing stands to more than 1 ha. Seed can be collected when available and ripe (Nov-Dec), but must be used within 18 months.
  • Fence existing stands and exclude domestic livestock. Occasional light grazing may be used if natives are not flowering or seeding.
  • Identify and control feral animals, particularly pigs.
  • Note the extent of grazing by native animals and obtain permits for control if necessary.
  • Develop and implement a fire reduction plan.
  • If establishing exotic pastures, maintain a wide (500 m) buffer of native pasture around Brigalow stands.
  • Retain all fallen timber and leaf litter within Brigalow stands as these are important habitat for some wildlife.
  • Retain mistletoe as these provide food sources for birds and mammals.

Ecosystem function: how healthy woodlands work for you

Healthy Brigalow provides a wide range of benefits that are called 'ecosystem services'. These include:

  • financial benefits
  • capture of solar energy
  • soil formation and cycling
  • nutrient cycling
  • water capture, filtration and delivery to water bodies
  • pollination
  • pest management (e.g. reducing pest pressure on crops)
  • regional climate buffering
  • shade and shelter (e.g. for livestock)
  • breakdown and absorption of wastes
  • a sense of place
  • scenery

Further Information

Look for "Brigalow" on the EPBC Species Profiles and Threats database (SPRAT) at
http://www.environment.gov.au/biodiversity/threatened/index.html.

The listing for this community under the NSW Threatened Species Conservation
Act can be found at
http://www.environment.nsw.gov.au/determinations/BrigalowEndComListing.htm

Contact the Border Rivers-Gwydir Catchment Management Authority at
02 6728 8020 or visit our website at http://www.brg.cma.nsw.gov.au

 

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