«Advice to the Minister for the Environment, Heritage and the Arts from the Threatened Species Scientific Committee (the Committee) on an Amendment to ...»
Advice to the Minister for the Environment, Heritage and the Arts from the Threatened
Species Scientific Committee (the Committee) on an Amendment to the list of
Threatened Ecological Communities under the Environment Protection and Biodiversity
Conservation Act 1999 (EPBC Act)
1 Name of the ecological community
Natural grasslands on basalt and fine-textured alluvial plains of northern New South
Wales and southern Queensland.
This advice follows the assessment of:
i. A nomination to list the Austrostipa aristiglumis Grasslands of the Liverpool Plains in NSW as an endangered ecological community under the EPBC Act 1999, and ii. A review of the listed Bluegrass (Dichanthium spp.) dominant grasslands of the Brigalow Belt Bioregions (North and South) ecological community.
The listing for the endangered Bluegrass (Dichanthium spp.) dominant grasslands of the Brigalow Belt Bioregions (North and South) was reviewed through technical workshops and discussions with relevant experts. The two key outcomes from the review were that the listed ecological community be split into two separately listed grassland ecological communities and that their definition not be limited to grasslands dominated by Bluegrass. The review recognised separate northern and southern grassland communities divided on climatic, geographic and floristic grounds. The northern community is centred on the Queensland Central Highlands and Fitzroy River Basin within the Brigalow Belt North bioregion. The southern ecological community occurs on the Darling Downs, Liverpool Plains and Moree Plains, mostly in the Brigalow Belt South and Darling Riverine Plains bioregions of Queensland and New South Wales (NSW). Temperate grassland species (e.g. Austrostipa aristiglumis) are present in the southern grassland but are largely absent in the northern grassland.
2. Public Consultation i. Public consultation was held on the nomination for ‘Austrostipa aristiglumis Grasslands of the Liverpool Plains in NSW’ in 2005.
ii. Public consultation was again held on the nomination and workshop reports in 2008.
The nomination and reports on technical workshop outcomes were made available for public exhibition and comment for the minimum required period of 30 business days. The Committee has had regard to all public and expert comment that was relevant to the consideration of the ecological community.
3. Summary of Conservation Assessment by The Committee The Committee provides the following assessment of the appropriateness of the ecological community's inclusion in the critically endangered category in the EPBC Act list of
threatened ecological communities:
The Committee judges that the ecological community has been demonstrated to have met sufficient elements of Criterion 1 to make it eligible for listing as critically endangered;
The Committee judges that the ecological community has been demonstrated to have met sufficient elements of Criterion 2 to make it eligible for listing as endangered;
The Committee judges that the ecological community has been demonstrated to have met sufficient elements of Criterion 4 to make it eligible for listing as vulnerable;
The highest category for which the species is eligible to be listed is critically endangered.
Natural grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Qld Listing Advice - Page 1 of 30
4. Description Native tussock grasslands, such as the Natural grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Queensland, once occurred over a large area of Australia (DEWR 2007). The species composition of tussock grasslands varies throughout its range and is influenced by factors such as rainfall, soil, geology and land use history. These influences may vary the expression of the ecological community over short periods or across small distances (Butler 2007 unpublished).
Many grass genera that occur as grassland dominants cover a diversity of habitats (Beadle 1981). The broad distribution of grass species is driven by climate although soil properties, such as salinity, fertility or waterlogging may override climate in determining the distribution of certain taxa (Beadle 1981).
Climate The Natural Grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Queensland ecological community occurs in a climatic zone with a wet summer and low winter rainfall pattern. The Darling Downs and Liverpool Plains components generally lie within the 550-750 mm mean annual rainfall isohyets whilst the Moree Plains component has a lower mean annual rainfall of about 400-550 mm. The Darling Downs has a predominantly summer rainfall pattern whilst the Liverpool Plains has a mainly winter rainfall pattern.
Landform and soil The distribution of the ecological community is strongly reliant on soil type as it is associated with fine textured, often cracking clays derived from either basalt or quaternary alluvium. The clay minerals in these soils are generally expanding i.e. upon wetting, water is absorbed into the clay particles causing them to expand. On drying, the water is released and the clay particles shrink. This expansion and contraction means that these soils are cracking or selfmulching. The high water-holding capacity of the clay soil inhibits deep penetration during most rainfall events. The development of deep cracks as the soils dry, and the tearing of tap roots during the soil contraction and expansion cycle are possible reasons why trees and large woody shrubs are typically lacking in these grasslands (Beadle 1981; Fensham 2003; Whalley pers. comm. 2007).
The ecological community generally occurs on flat to low slopes, of no more than 5 percent (or less than 1 degree) inclination. As slope increases, grassy woodlands dominated by trees such as Acacia pendula (Weeping Myall), Eucalyptus coolabah (Coolabah), E. populnea (Poplar Box) or E. melliodora (Yellow Box) occur. The ground layer component of these woodlands may be similar to the grassland but the soils will not be the same cracking clays as on the plains (Benson et al. 2006).
Vegetation Ground layer Native grasslands are dynamic ecosystems where species composition can change yearly and seasonally in response to rainfall, temperature, fire, grazing pressure and management (Langford 2005). Temperate grasslands are typically dominated by tussock grasses in the genera Austrodanthonia, Austrostipa, Bothriochloa, Chloris, Enteropogon, or Themeda (Carter et al. 2003). Representatives of these genera, as well as temperate grassland forbs, are present to some extent throughout the ecological community.
Natural grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Qld Listing Advice - Page 2 of 30 The presence of a temperate component is one feature that distinguishes this ecological community from the related, truly tropical native grasslands in the Queensland Central Highlands (Fensham 1999). It should be noted that the dominance of temperate grasses in the Liverpool Plains may be a consequence of past management practices and is not necessarily an indication of their pre-European abundance. Although Carter et al. (2003) classified the grasslands of the Liverpool Plains as temperate on the basis of their dominance by Austrostipa, there is evidence that such dominance is a consequence of past management practices and that their true affinities lie with the grasslands in the Darling Downs (Keith
2004) rather than the more southern grasslands.
In the Darling Downs component of the ecological community, Dichanthium sericeum (Bluegrass) tends to be the dominant grass species. In the Liverpool Plains component of the ecological community, Austrostipa aristiglumis (Plains Grass) tends to dominate. Drier sites of the ecological community may include a higher proportion of Astrebla spp. (Mitchell Grass). However, the Darling Downs grasslands also include Austrostipa arisitiglumis as a significant winter growing component (Beadle 1981).
It is important to note that native grasslands comprise not only the more obvious grass species, but also a great diversity of other herbaceous plants such as native daisies, orchids, lilies and other wildflowers. Many of these plants are only easily seen in the spring (Barlow 1998; Eddy 2002). The native grassland flora also includes herbaceous legumes such as Desmodium, Glycine, Lotus and Rhynchosia that have an important role in soil nitrogen fixation. The native legumes of grasslands on the Liverpool Plains are now mainly restricted to sites that have not been heavily degraded by past land management practices (Whalley pers. comm. 2007).
Shrub layer The shrub cover is typically a very minor component of the grassland however in some areas such as Kirramingly (south of Moree) the cover of shrubs, such as Acacia farnesiana (Mimosa), can be quite thick (Clarke 1998). At sites like this, the thick shrub cover does not affect the abundance of grass species. Other shrubs that may be present include Pittosporum phylliraeoides, Pimelea spp. and Sclerolaena spp. The total projective canopy cover of woody shrubs over 0.5 m tall can be up to 50% in this ecological community but is typically much less.
Tree canopy A tree canopy is typically absent. Where trees are present, they are of variable species composition and comprise less than 10% of projective crown cover. Tree species that may be present as scattered individuals include: Acacia pendula (Weeping Myall), Eucalyptus albens (White Box), E. conica (Fuzzy Box), E. coolabah (Coolabah), E. melliodora (Yellow Box), E. populnea (Poplar Box) or E. tereticornis (Forest Red Gum).
Key diagnostic characteristics:
The Natural Grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Queensland ecological community may be recognised by the following diagnostic
Distribution mainly in the Darling Downs of southern Queensland and the Liverpool Plains and Moree Plains of northern NSW. Occurrence is mainly associated with fine textured, often cracking clay soils derived from either basalt or alluvium.
Occurrence on landforms that are typically flat to very low slopes (less than 5 percent/1 degree).
Natural grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Qld Listing Advice - Page 4 of 30 (Butler 2007 unpublished). Grasslands also support an array of raptors including widespread species such as Falco berigora (Brown Falcon) as well as more grassland dependent species such as Circus assimilis (Spotted Harrier) (Butler 2007 unpublished).
The mammalian fauna of grasslands has been grossly depleted since European settlement and many of the smaller mammals are now extinct (Lunt 1991). Nevertheless, native mammals still play an important role in many ecosystems. Macropus giganteus (Eastern Grey Kangaroos) are very selective grazers, feeding almost exclusively on monocotyledons, particularly grasses. Forbs and woody plants are not significantly grazed, despite their higher nutritive value (Lunt 1991). However, the impact of kangaroo grazing depends on the population density. High population levels severely degrade vegetation and restrict the regeneration of many rare and threatened plants (Lunt 1991).
A list of the vertebrate animal species that may utilise this ecological community for food and habitat is at Appendix A.
5. Condition Thresholds There are very few patches of undisturbed native grasslands remaining. Most patches now have some degree of disturbance and degradation. The listed Natural grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Queensland ecological community comprises those patches that meet the key diagnostic characteristics, above, and the condition thresholds in Table 1, below. Both the best and good quality are included in the listed ecological community.
Table 1. Condition thresholds for the Natural grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Queensland ecological community.
Best quality Good quality Minimum patch size at least 0.5 ha Minimum patch size at least 2 ha Patch size AND AND At least 4 native perennial grass At least 3 native perennial grass Grasses species from the indicator species species from the indicator species list list AND AND At least 200 native perennial grass At least 200 native perennial grass Tussock tussocks AND tussocks AND cover Total projected canopy cover of Total projected canopy cover of Woody shrub cover1 shrubs is less than 30% AND shrubs is less than 50% AND Perennial non-woody introduced Perennial non-woody introduced Introduced weed species are less than 5% of weed species are less than 30% of species the total projected crown cover the total projected crown cover 1 Shrubs are typically absent. When present, they are defined as woody plants more than 0.5 m tall that occupy the mid vegetation layer. The upper, tree canopy layer also is typically absent but may comprise scattered trees to less than 10% projective crown cover.
Sampling should be based upon a quadrat size of 0.1 ha (e.g. 50 m x 20 m) selected in an area with the most apparent native perennial grass species. Unless exceptional circumstances apply, to maximise the assessment of condition, a site must be assessed during a good season, two months after cessation of disturbance (fire, grazing, mowing or slashing) and within two months of effective rain.
The Brigalow North and South (Queensland and NSW) is recognised as one of 15 National Biodiversity Hotspots.
Relationships to national and State vegetation classification systems The National Vegetation Information System (NVIS) is a systematic and hierarchical approach to classifying native vegetation at the national scale. The Natural grasslands on basalt and fine-textured alluvial plains of northern NSW and southern Queensland is classified within NVIS as part of Major Vegetation Group (MVG) 19 Tussock Grasslands.
Tussock grasses occur on heavy clay soils that have few woody species and extend over a large area of the mainland from the Gulf of Carpentaria to the basalt plains of western Victoria (Keith 2004, DEWR 2007).