Natural grasslands on basalt and fine-textured alluvial plains of northern New South Wales and southern Queensland - profile

Gazetted date: 07 Jan 2009

Profile last updated: 01 Nov 2022

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may vary the expression of the ecological community over short periods or across small distances (Butler 2007 unpublished).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. 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 features: 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). Tree canopy usually absent to sparse, comprising less than 10% projective crown cover. The ground layer is typically dominated by perennial native grasses and contains 3 or more of the indicator native species listed below. Aristida leptopoda White Speargrass Astrebla elymoides Hoop Mitchell Grass Astrebla lappacea Curley Mitchell Grass Austrodanthonia bipartita Wallaby Grass, Bandicoot Grass Austrostipa aristiglumis Plains Grass Bothriochloa biloba Lobed Bluegrass Bothriochloa erianthoides Satin Top Grass Dichanthium sericeum Queensland Bluegrass Digitaria divaricatissima Umbrella Grass Elymus plurinervis Wheat Grass Eriochloa crebra Cup Grass Eulalia aurea Silky Brown Top Panicum decompositum Native Millett Panicum queenslandicum Yabila Grass Thellungia advena Coolibah Grass Themeda avenacea Native Oat Grass Themeda triandra (synonym. T. australis) Kangaroo Grass Walwhalleya proluta Rigid Panic Note that in a poor season, as in a hot summer or drought, the only visible evidence of natural grassland may be scattered tussocks that are difficult to identify as any particular species. It is therefore, highly desirable to identify and assess the condition of the ecological community during a good season (see: section 5. Condition Thresholds). Fauna Many animals that forage and feed in grasslands also shelter and breed in other habitats where woody plants provide structural features that are absent in grasslands (Keith 2004). In the Brigalow Belt South Bioregion 10 mammals (including Lagorchestes leporides (Eastern Hare Wallaby)) have become extinct (Keith 2004), and there have been major declines in the abundance of ground-feeding insectivorous and grassland birds (National Land and Water Resources Audit 2007). Deep cracking black soils are a key habitat characteristic for some of the more grassland dependant fauna, particularly reptiles such as Anomalopus mackayi (Five-clawed Wormskink), Tympanocryptis pinguicolla (Grassland Earless Dragon) and numerous other lizards and snakes (Hobson 2002). Within the ecological community deep soil cracks in these grasslands are habitat for small mammals such as Planigale tenuirostris (Narrow-nosed Planigale), P. ingrami (Long-tailed Planigale), P. maculata (Common Planigale) and Rattus tunneyi (Pale Field-rat) (Butler 2007 unpublished). Grassland birds may be dependent upon the structural complexity of grassland vegetation. Well developed grass tussocks and inter-tussock spaces of varying size and character as well as forbs, twining herbs and decaying vegetation provide structural complexity in grasslands. Vegetation cover provides nesting material and protection from avian predators for granivorous birds like Coturnix ypsilophora (Brown Quail), Coturnix pectoralis (Stubble Quail), Turnix velox (Little Button Quail), and Turnix pyrrhothorax (Red-chested Button Quail) as well as insectivores like Cincloramphus mathewsi (Rufous Songlark), Cincloramphus cruralis (Brown Songlark), and Cisticola exilis (Golden-headed Cisticola) (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). In order to meet the definition of the TEC sites must satisfy condition criteria stipulated in the Listing Advice and/or Conservation Advice. Typically condition is assessed by reference to patch size and vegetation structure thresholds or species composition metrics.