Plains mallee box woodlands of the Murray Darling Depression, Riverina and Naracoorte Coastal Plain Bioregions - profile

Gazetted date: 10 Jun 2021

Profile last updated: 05 Oct 2023

The ecological community occurs within the following bioregions (Interim Biogeographic Regionalisation of Australia, IBRA V7, DoE 2012): • Murray Darling Depression Bioregion (NSW, SA, Vic) • Riverina Bioregion (NSW, Vic) • Naracoorte Coastal Plain (SA) – Tintinara subregion (NCP04) Within these bioregions, the ecological community typically occurs on near-level plains or occasionally on gently sloping terrain surrounding and within run-on landscape depressions where soil textures are typically clay loams, but may occasionally be sandy clay loams or light clays (see Section 2.1.2.1 below). The ecological community is associated with areas with an average annual rainfall (MAR) typically in the range of 260mm – 450mm, within semi-arid to arid regions of the Murray Darling Depression, Riverina and Naracoorte Coastal Plain Bioregions. In Victoria, it occurs primarily on Woorinen Formation plains (Lawrence 1966; 1980) and occasionally alluvial plains from the border with South Australia between the two Lowan Formation sand sheets (Lawrence 1966; 1980) known as the Little Desert and the Big Desert. It extends in an easterly direction towards Charlton, Boort and Kerang on the southern boundary, with a northern boundary more or less constrained by the Murray River. Outlier occurrences may also occur within the Little Desert, Big Desert and Natimuk areas (Sluiter & Schultz, 2020). In NSW, it occurs primarily in the Kyalite-Tooleybuc-Koraleigh-Speewa area with possible extensions east toward Moulamein (Sluiter & Schultz, 2020). In South Australia, it occurs in the following regions and in the vicinity of associated localities: Western Murray Flats: Monarto to Walker Flat and north to Swan Reach; Southern Murray Mallee: Murray Bridge-Tailem Bend-Wynarka-Karoonda-Wanbi; and Upper South East: Bordertown-Keith-Tintinara-Coonalpyn (Sluiter & Schultz, 2020). The Plains mallee box woodlands ecological community occurs within the traditional lands of many Aboriginal groups7 from south-west New South Wales, north-west Victoria and southeast South Australia. These include, but may not be limited to, the Wergaia, Latji Latji, Ngintait, Nyeri Nyeri, Barapa Barapa, Dja Dja Wurung, Wemba Wemba, Wadi Wadi, Nari Nari, Dadi Dadi, Madi Madi, Kureinji, Jardwadjali, Bindjali, Ngardad and Meru. The ecological community is likely or known to occur (at the time of writing) within the following Natural Resource Management regions: Victoria – ‘Mallee’, ‘North Central’ and ‘Wimmera’ Catchment Management Authority regions; NSW – the ‘Murray’ (western edge) and ‘Western’ (near Balranald) Local Land Services regions; and,South Australia – the ‘South Australian Murray Darling Basin’ (Murraylands and Riverland Landscape Board) and ‘South East’ (Limestone Coast Landscape Board) Natural Resources Management regions. The ecological community is likely or known to occur (at the time of writing) within or adjacent to the following Local Government Areas: Victoria – Buloke Shire, Gannawarra Shire, Hindmarsh Shire, Horsham Rural City, Loddon Shire, Mildura Rural City, Swan Hill Rural City, West Wimmera Shire, Yarriambiack Shire. NSW – Balranald Shire Council, Edward River Council, Murray River Council. South Australia – Coorong District Council, Mid Murray Council, Southern Mallee District Council, Tatiara District Council, The District Council of Loxton Waikerie, The District Council of Karoonda East Murray, The Rural City of Murray Bridge. 2.1.2.1 SOILS Soils are variable but are typically duplex, with clay loam or occasionally sandy clay loam topsoil textures mostly of Woorinen Formation aeolian origin, above deep fine textured clay subsoils. Typically, they are heavier in texture than soils that support most other mallee vegetation, but have a lower fraction of clay than soils supporting other vegetation in the region, such as saltbush shrublands and black box woodlands. In Victoria and NSW, topsoil colours range in Hue (Munsell (2009) from red (10R) (less common), through reddish-brown (2.5YR and 5YR), to brown (7.5YR) and greyish-brown to yellowish-brown (10YR). The latter primarily occurring where Yamba Formation gypsums occur as the sub-soil clay. Soils are typically Chromosols, Calcarosols or occasionally Vertosols (Sluiter & Schultz, 2020). The biological soil crust (BSC) is a functionally important component of the Plains mallee box woodlands ecological community, closely associated with the top few millimetres of soil (Duncan et al., 2007a). Where disturbance is minimal, and conditions are suitable, the BSC can reach up to 60% ground cover and is dominated by mosses and some lichens, as well as liverworts, cyanobacteria, algae and fungi (Read et al., 2011, Duncan et al., 2007b, Eldridge & Green 1994). Key functions of the BSC include: stabilising soils against water and wind erosion; regulating water infiltration and wind erosion; fixing atmospheric nitrogen and carbon dioxide, facilitating nutrient cycling; providing habitat for microfauna; and facilitating the recruitment of vascular plants through seed entrapment and germination (Read et al., 2011, Duncan et al., 2007b, Eldridge & Green 1994). 2.1.3 Vegetation structure The canopy of Plains mallee box woodlands is mostly medium (5-10 m) to occasionally tall (to 15 m). Tree canopy cover8 is typically sparse or open (10-15%). A small tree and/or large shrub layer may be present, but is typically low (3-5 m) and very sparse with < 5% cover. A medium shrub layer 1-3 m tall may also be present, but is also normally very sparse (< 10% cover). A distinctive low to decumbent chenopod sub-shrub layer can be a key feature in many occurrences. The ground layer is dominated by tussock grasses, but may be inconspicuous depending on drought conditions or livestock and other ground disturbance. Soil types, landscape settings, fire regimes, grazing regimes and climate variation interact to affect the dynamics of the mallee vegetation present in any area. As a result of past disturbances (notably clearing for agriculture and/or heavy grazing), the understorey of the ecological community is highly variable and reflects both local environmental conditions and prior land-use. The latter may enable establishment of introduced plants, notably annual forbs and grasses. 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.