MVG 32 Open Mallee Woodlands and Sparse Mallee Shrublands DRAFT
Total Page：16
File Type：pdf, Size：1020Kb
MVG 32 – OPEN MALLEE WOODLANDS AND SPARSE MALLEE SHRUBLANDS Triodia mallee, western NSW (Photo: B. Pellow) Overview Mallee Woodlands and shrublands are semi-arid systems dominated by eucalypt species that produce multiple stems from an underground rootstock known as a lignotuber. Some vegetation in non-arid regions also supports eucalypts with mallee growth forms, but these are not part of MVG 32 or MVG 14. Eucalypts are the most widespread tree component of this MVG however species of Callitris, Melaleuca, Acacia and Hakea may co-occur as trees at varying densities and may co-dominate mallee communities. An open tree layer (notionally < 10 % projective foliage cover, < 20% crown cover) distinguishes MVG 32 from MVG14 (Mallee Woodlands and Shrublands), which has a denser tree layer (notionally >10% foliage projective cover, >20% crown cover). However, this distinction is largely artificial, as tree cover varies spatially at fine scales and temporally with fire regimes, while the occurrence of tree, shrub and ground layer species shows little relationship to variations in eucalypt cover. Understorey composition is strongly influenced by rainfall, soil types and fire regime and can be dominated by hummock grasses (spinifex), chenopods or other woody shrubs. Some mallee woodlands are among the most fire prone of all plant communities in semi-arid and arid zones (Keith 2004). Facts and Figures Major Vegetation Group MVG 32 – Open Mallee Woodlands and Sparse Mallee Shrublands Major Vegetation Subgroups 61. Chenopod Mallee NSW, SA, VIC. (111) (number of NVIS descriptions) 55. Shrubby Mallee NSW, SA, VIC. (37) 27. Triodia Mallee NSW, SA, VIC. (150) 29. Heathy Mallee SA, VIC. (280) xx. Western Mallee WA (XX) Typical NVIS structural formations Open mallee woodland (mid, low) Open mallee shrubland (mid, low) Number of IBRA regions 40 Most extensive in IBRA region Est. pre-1750: Murray Darling Depression (NSW, SA and Vic) Estimated pre-1750 extent (km2) 387 230 Present extent (km2) 271 529 Area protected (km2) 99 969 Chenopod mallee, western NSW (Photo: B. Pellow) Structure and physiognomy Woodlands and shrublands dominated by low, multi-stemmed, sclerophyllous eucalypts and occasionally small trees from other genera with a spares to dense understorey. Height of eucalypt canopy varies from 2 to 10 m (Bradstock and Cohn 2002). Tree canopy cover varies with rainfall, topographic position, soil characteristics and particularly fire history, but projective foliage cover is notionally within < 10% and crown cover is notionally < 20%. Understorey structure also varies with rainfall, topographic position, soil characteristics and particularly fire history, and may be dominated by sclerophyllous or non-sclerophyllous shrubs, hummock grasses, chenopods or tussock grasses. Ground layer is strongly influenced by recent rainfall and fires. In drought the ground layer is spares while following heavy rainfall a prominent cover of ephemeral herbs with tussock grasses occurs. A soil crust forms on flat areas and local depressions, comprising cyanobacteria, lichens and mosses, but is largely absent from dune crests and slopes. The major vegetation subgroups of this MVG differ in terms of canopy dominants, understorey composition, soil characteristics and topographic position (Haslem et al. 2010). Indicative flora Eucalypts of the semi-arid mallee woodlands belong almost entirely to sections Bisectaria and Dumaria within the subgenus Symphyomyrtus, although a few species belong to sections Adnataria, also within Symphyomyrtus (Hill 1989). See further discussion in Notes below. Widespread mallee tree species include Eucalyptus dumosa, Eucalyptus socialis, Eucalyptus gracilis, Eucalyptus oleosa, and Eucalyptus calycogona. Distinctions between the five Major Vegetation Subgroups are based mainly on the perennial components of the understorey. o Chenopod mallee subgroup understorey includes species of Maireana, Sclerolaena, Enchylaena, Chenopodium and Zygophyllum. Eucalyptus oleosa, Eucalyptus gracilis, Eucalyptus dumosa and Eucalyptus calycogona are the most commonly occurring trees, while Callitris verrucosa and Triodia are essentially absent. It occurs on shallow sandplains with heavier textured soils associated with shallow calcrite subsoils across New South Wales, Victoria and South Australia (Cheal and Parkes 1989; Sparrow 1989; Haslem et al. 2010). o Shrubby mallee subgroup includes a range of mostly non-sclerophyll shrubs from genera such as Senna, Acacia, Dodonaea, Myoporum, Eremophila, Enchylaena, Sclerolaena, Melaleuca, Grevillea, Hakea, and Westringia. Triodia and Callitris are very uncommon in these communities and biological soil crusts are typical except where disturbed by livestock. Any of the major mallee eucalypts may be locally dominant in Shrubby mallee, It occurs where calcite subsoils are below moderate depths of red loamy sand in dune swales and flat sandplains across New South Wales, Victoria and South Australia (Sparrow 1989; Keith 2004; Haslem et al. 2010). o Triodia mallee subgroup has an understorey dominated by hummock grasses (Triodia scariosa and Triodia irritans) interspersed with small trees or shrubs of genera such as Acacia, Callitris, Eremophila and Beyeria. The principal eucalypts are Eucalyptus costata, Eucalyptus socialis and Eucalyptus dumosa. It typically occurs over the summits and slopes of dunes across the lower Murray and Eyre districts of New South Wales, Victoria and South Australia (Keith 2004; Haslem et. al. 2010). o Heath mallee subgroup is typified by more sclerophyllous shrub genera, with Callitris verrucosa often prominent in either the tree or shrub layer. Typical shrub genera include Acacia, Aotus, Baeckea, Leptospermum, Melaleuca, Beyeria, Brachyloma, Hibbertia, Cryptandra, Spyridium and Phebalium. Eucalyptus costata is the most common tree, but other species occur frequently. Triodia may occur sparsely among the shrubs. Heathy mallee is typically found on white sandplains in south western Victoria and the adjoining area of south eastern South Australia, as well as the Eyre Peninsula (Sparrow 1989; Cheal & Parkes 1989; Haslem et al. 2010). There is a transition to true heathlands within increasing rainfall to the south (Cheal & Parkes 1989). o Western mallee subgroup is characterised by several eucalypts some of which are endemic to Western Australia, including Eucalyptus eremophila, Eucalyptus moderata, Eucalyptus oleosa, Eucalyptus incrassata, Eucalyptus foecunda, Eucalyptus redunca and Eucalyptus uncinata (Beard et. al 2013). The understorey is predominantly shrubby with species of Melaleuca and Acacia, and occasional Triodia. It is widespread in the southern goldfield regions, extending eastward to the coast of the Great Australian Bight (Beard et al. 2013). Ephemeral herbs from a wide range of plant families are abundant after rain including the Poaceae (mainly Austrostipa), Asteraceae, Goodeniaceae, Solanaceae, Apiaceae, Brassicaceae and Zygophyllaceae. Eucalyptus gracilis (yorrell) with Beyeria opaca and Triodia sp. Calperum, near Renmark, SA (Photo: M. Fagg) Environment Typically semi-arid Mediterranean with cool winters and hot dry summers, and annual rainfall of between 200 – 500 mm per annum occurring predominately in winter. Occurs on calcareous sandplains, predominantly with lateritic soils in western Australia and on Aeolian landscapes in eastern Australia (Bradstock and Cohn 2002). Different geomorphic processes have shaped these mallee regions with much of the central and south-eastern mallee characterised by sand dune and swale systems (Hill 1989). In many areas the variation in the thickness of surface sand above clay or calcareous hard pan affects the structural and floristic composition of mallee (Bradstock and Cohn 2002). Soils associated with mallee of arid Australia include solonized brown soils, siliceous sands, calcareous sands, solodized solonetz, soloths, earthy sands and calcareous red earths (Blackburn and Wright 1989). Geography Located in the semi-arid areas of southern Australia in southwest New South Wales, northwest Victoria, southern South Australia and southern Western Australia. Largest area occurs in South Australia (126 804 km2). In the east mallee is largely restricted to the sandplains and sand dunes of the western part of the Murray Basin with small areas occurring on landforms of Aeolian origin further north (Wassan 1998). In the west mallee occurs on three main land forms the Yilgarn Plateau, the Stirling coastal zone and the Nullarbor Plain (Wassan 1998). Centrally, in South Australia mallee occurs on extensive dunefields of the Eyre Peninsula, the lower Murray and in the Gulf Ranges provinces (Wassan 1998). Make up the most arid of the eucalypt-dominated communities of temperate Australia (Parsons 1994). Change Approximately 30% of the estimated pre-1750 extent cleared accounting for 11.4% of total clearing in Australia including large areas of southern Western Australia and South Australia and northern Victoria. Losses have been disproportionate, and greatest by far in the Chenopod mallee subgroup (Sparrow 1989; Cheal & Parkes 1989). Approximately 116 000 km2 cleared since European settlement. Clearing for crops is ongoing, albeit at reduced rates. Legacies of fragmentation continue to degrade ecological functions. Removed from many cereal cropping and sheep grazing lands in the southern and eastern parts of Australia over the last 100 years, most recently for irrigated vineyards and orchards. Clearing of the mallee