Natural Grasslands on Alluvial Plains

Natural Grasslands on Alluvial Plains is the name given to the threatened ecological community Natural Grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Queensland. This grassland occurs on fertile alluvial soils across our catchments and is characterised by perennial tussock grasses such as Mitchell grasses, Plains grass and Queensland blue grass. It usually has a diversity of grass species, saltbushes and herbs with occasional shrubs.

Large areas of these grasslands have been cleared for cropping in the catchments and remaining fragments are listed as critically endangered. The grassland and its waterways provide an essential home to many of our catchments' most threatened species.

Natural Grasslands on Alluvial Plains 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 Natural Grasslands on Alluvial Plains may require consent or approval.

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Where does the community occur?

Natural Grasslands on Alluvial Plains are usually found on the Liverpool Plains, the Moree Plains and the Darling Downs (Qld). On the Liverpool Plains, the community is usually dominated by Plains grass, while on the Darling Downs, Queensland blue grass dominates. Mitchell grass is usually the dominant species in drier parts of the distribution.

Within the Border Rivers-Gwydir catchment, the community is found in the following IBRA sub-regions: Nandewar North, Peel, Kaputar, Inverell Basalts, Northern Outwash, Northern Basalts and Castlereagh – Barwon.

Identification

Natural Grasslands on Alluvial Plains is a community that changes with seasonal  conditions. It is a grassland community dominated by perennial tussock grasses. The dominant grass species are usually Mitchell grasses (Astrebla spp.), Plains grass (Austrostipa aristiglumis), Queensland blue grass (Dichanthium sericeum), Kangaroo grass (Themeda australis), Yadbila (Panicum queenslandicum) or one of 13 other indicator grass species. There may be many grass species present, with several co-dominating. The composition of the grassland will change according to seasonal rainfall, temperature, fire and management.

These grasslands are usually found on cracking clay soils. The soils where they occur are derived from basalt or are alluvial, quaternary soils. They occur on plains with a slope less than 5o.

Natural grasslands have very few trees or shrubs, but will have a diversity of herb species including legumes, orchids, daisies and lilies.

What is not Natural Grasslands on Alluvial Plains?

Many other ecological communities have a grassy understorey, with many species in common with Natural Grasslands on Alluvial Plains. These include Weeping Myall,  Coolibah – Black Box Woodland and Box-Gum Grassy Woodland, which are also  threatened ecological communities. These communities, and other grassy woodlands like Bimble Box Grassy Woodland, have a higher cover of trees and shrubs than Natural Grasslands on Alluvial Plains.

Threats

Clearing – conversion of native grasslands to cultivation for cropping is now illegal under the Native Vegetation Act 2003, but still occurs due to a lack of awareness of the conservation significance of grasslands. Before converting any pasture to cropping or sewn pasture, consult the CMA about your responsibilities. Clearing for mining is also a significant threat.

Grazing – knocks out highly palatable or vulnerable species such as legumes. There can also be a change in the dominant species from Austrostipa and Dichanthium to Chloris species, then Sporobolus species and finally a mixture of unpalatable weeds. Undergrazing can also be a threat, as tussock grasslands will become simpler unless the biomass of the dominant tussock grass species are occasionally reduced by fire or grazing.

Weed invasion – weedy perennial grasses present the greatest threat to this community. The main threatening species are: Coolatai grass (Hyparrhenia hirta), African love grass (Eragrostis curvula), Buffel grass (Cenchrus ciliaris) and Green Panic (Panicum maximus). The establishment of some of these species as 'improved' pastures adjacent to grassland communities is a significant threat. Lippia (Phyla nodiflora) is a major threat in periodically-inundated areas. Mimosa (Vachellia farnesiana) and African boxthorn (Lycium ferocissima) are less of a threat but do displace grassland species. Changed flooding regimes – alter the species composition of natural grasslands, often favouring weed species. These changes may come about through irrigation, road construction, building of floodplain structures or channel construction.

Changed fire regimes – affect grassland communities by changing species composition and relative abundance. Too frequent fire can encourage fire tolerant species like Coolatai grass over native species. Feral animals – pigs can cause significant localised damage to grasslands by uprooting plants and creating opportunities for weed invasion. The house mouse competes with grassland fauna for food and habitat, particularly during high population outbreaks. Disturbance from rabbit burrowing and grazing can also alter species composition.

Climate change – can result in changes to water availability and fire regimes. It is also likely to change the distribution and impact of weed species.

Lack of awareness – of the importance or scarcity of this vegetation community is a major threat as some farmers carry out destructive acts without even knowing the significance of grassland communities.

Management

The aim of management of Natural Grasslands is to maintain or increase the extent of the community and to maintain or improve its condition.

Grazing Management – should aim to increase the diversity of species in degraded stands, and to allow natural fluctuations in species composition in response to seasonal conditions to occur. A mix of occasional short, heavy grazing and regular light stocking is likely to favour optimal stand development and survival.

Avoid grazing when the soil is saturated to prevent pugging, particularly on grey clays. Where possible, avoid grazing when plants are flowering and setting seed.

Not converting to cropping – before ploughing new areas for cropping, assess whether or not the site supports Natural Grassland. Seek advice from the CMA if you are unsure. Don't allow cultivation to creep into adjacent grassland areas.

Restoration – natural grasslands can be re-established over time through assisted regeneration and revegetation. Previously cropped areas can be left to regenerate, provided invasive grasses are controlled. Avoid planting trees or dense shrub cover into areas of Natural Grasslands. Seed of many grassland grasses is available from commercial seed suppliers.

Increasing awareness – become more aware of the occurrence and extent of Natural Grasslands on your property and in your district. Many of the few remaining stands are located on stock routes and roadsides and can be inadvertently destroyed by road maintenance, grading, dumping soil or inappropriate fire or grazing regimes. Natural grasslands are most likely to occur on parts of your property where cropping does not occur, such as adjacent to waterways, in rocky areas or around areas of other native vegetation.

Controlling and not spreading weeds – spot spray small outbreaks of invasive grasses in and around patches of Natural Grassland. Cut and paint the stumps of invasive shrubs such as African boxthorn with glyphosate. When maintaining roads avoid bringing machinery from weedy areas into stands of grassland and avoid cutting drains or dumping soil in grassland patches.

Ecosystem function: how healthy woodlands work for you

Healthy Natural Grasslands on Alluvial Plains provide a wide range of benefits that are often called 'ecosystem services'. These include traditional services like grazing for livestock, but also other services such as:

  • financial benefits
  • 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 "Natural Grasslands" on the EPBC Species Profiles and Threats database (SPRAT) at
www.environment.gov.au/biodiversity/threatened/index.html.

Commonwealth Listing Advice on Natural grasslands on basalt and fine-textured alluvial plains of northern New South Wales and southern Queensland.
www.environment.gov.au/biodiversity/threatened/communities/pubs/88-listing-advice.pdf

Nadolny C., Hunter J. & Hawes W. (2010) Native grassy vegetation in the Border Rivers-Gwydir Catchment: diversity, distribution, use and management. In: Report to the Border Rivers-Gwydir CMA.

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


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