A broad coastal plain running from Victoria to the end of the Younghusband Peninsula in South Australia, the Naracoorte Woodlands ecoregion has nearly all been converted for agriculture. Low topography, high rainfalls, and the complex drainage of the Murray River mouth result in large lakes, lagoons, and waterlogged areas. Several wetlands of international significance are found in this ecoregion. However, widespread clearing and fragmentation, combined with wetlands drainage and hydrological control mean that European settlement had a severe impact on this ecoregion.
Location and General Description
Situated along the mesic coastal strip in southeastern South Australia, all except the northernmost parts of this region have a cool, moist Mediterranean climate. Mean annual rainfall ranges from around 400 mm in the north (Laut 1977b) to over 850 mm in the south (Laut 1977a). Much of the region consists of undulating plains characterized by low parallel sand dunes underlain by calcrete, with several centers of geologically recent volcanic activity in the Mount Gambier district. The low topography coupled with high rainfall results in many areas being waterlogged part of the year. An extensive series of freshwater lagoons lies behind the coastal foredunes along the southern part of the coastline, while to the north the complex set of lakes and lagoons associated with the Murray River mouth generates a series of shallow waterbodies grading from fresh- to saltwater.
The distribution of the original vegetation of the region was largely determined by rainfall and drainage, with open sclerophyll forests on better drained soils in the higher rainfall areas becoming open woodlands as rainfall declines. Heaths grow on sandy soils and open river red gum (Eucalyptus camaldulensis) woodlands in heavier soils in low-lying seasonally waterlogged areas, with Gahnia tussock sedgelands and swamps in the wettest parts (Laut 1977a, Specht 1972). The forest and woodland understories tend to have a species composition similar to the heath regions, being made up of Xanthorrhoea tussocks and small-leaved sclerophyllous shrubs (e.g., Acacia, Astroloma, Banksia, Calytrix, Epacris, Hakea, Leptospermum and Leucopogon spp.). The region has been extensively cleared for agriculture, primarily livestock grazing, viticulture, and plantation forestry.
Endemism is low, as much of the biota in this region can also be found in the adjoining Mount Lofty Woodlands ecoregion and the Southeast Australia Temperate Forests ecoregion. Several globally threatened species are, or were until relatively recently, found here. The critically endangered orange-bellied parrot (Neophema chrysogaster) (Hilton-Taylor 2000) overwinters among the coastal dune vegetation and saltmarshes. Two other endangered birds, the swift parrot (Lathamus discolor) and the regent honeyeater (Xanthomyza phyrigia), were regularly seen in the region 20 to 30 years ago but are now rarely if ever encountered. The striped legless lizard (Delma impar), which is considered vulnerable, is also found in forests and woodlands in the extreme southeast (Cogger 2000). The region is also the westernmost limit of the ranges of most pygmy-possums (Cercartetus spp.) and gliding possums (Petaurus spp. and Acrobates pygmaeus) (Strahan 1995).
The Naracoorte caves have recently been declared a World Heritage site, primarily on the basis of the rich Pleistocene megafauna fossil deposits they contain. The extant vertebrate cave fauna is less notable; the only bat species using the cave system, the common bentwing-bat (Miniopterus schreibersii), is abundant throughout a broad geographical range along the eastern coast of Australia (Strahan 1995). However, some of the arthropods collected from guano deposits appear to be endemic (NPWS 1992).
Perhaps the most notable feature of the region is the variety of saline and freshwater wetlands, which provide important habitats for waterfowl and migratory waders (Paton 1986). The Murray-Darling Basin covers approximately 14 percent of Australia and is one of the world’s largest river systems. Because Australia is mostly arid, the output from the Murray-Darling system is low, and no large fan delta results. Instead a series of shallow lakes drain into the ocean through a gap in coastal dunes that line the shore.
The Coorong in the northwestern section of the region is the major saline wetland area. Confined by the coastal dune barriers of the Younghusband and Sir Richard Peninsulas, the Coorong measures 140 km in length. The salinity levels in its lagoons vary from brackish to hypersaline, depending on location, time of year, and amount of flow through the mouth of the River Murray (Paton 1986). Many of the freshwater wetlands were originally temporary, the largest of these being Bool Lagoon (2,500 ha). Variability is important in these freshwater systems, for the composition of their aquatic plant communities is determined by flooding depth, season, frequency and duration (Rea 1994). The Coorong (with the adjacent Lakes Albert and Alexandrina) and Bool Lagoon are both designated as Ramsar Wetlands of International Importance.
Fauna of the Coorong includes migratory waders such as red-necked stints (Calidris ruficollis), sharp-tailed sandpipers (C. acuminata), and curlew sandpipers (C. ferruginea). Large numbers of grey teal (Anas gracilis) and Australian shelducks (Tadorna tadornoides) also utilize the Coorong. Water rats (Hydromys chrysogaster), eastern swamp rat (Rattus lutreolus), long-necked tortoise (Chelodina longicollis) and short-necked or Murray tortoise (Emydura macquarri) are found here as well (DEHAA 1999).
Over 90 percent of the region has been cleared (Stove 1998), and the remaining patches of vegetation are generally fragmented and relatively small. Few tracts larger than 10 km2 remain, and the larger tracts are predominantly long, narrow strips of land encompassing the coastal foredunes and lagoons. The largest remaining tracts are conserved in the Coorong National Park (465 km2), Messent Conservation Park (123 km2), and Canunda National Park (105 km2).
Mammalian extinction rates are high even by Australian standards (Strahan 1995), where nearly half of the world’s mammalian extinctions have occurred in the past 200 years (Short and Smith 1994). In this ecoregion, extinct species include taxa such as the toolache wallaby (Macropus greyi) that are above the critical weight range where the bulk of mammalian extinctions have occurred. Although regional plant extinctions are on a par with other regions in southern Australia, an unusually high proportion of the flora is considered to be threatened (Land and Kraehenbuehl 1987). Several woodland communities that were once widespread are now considered to be poorly conserved both regionally and nationally, while one freshwater aquatic herbland community is inadequately conserved regionally (Davies 1982).
Types and Severity of Threats
Overclearing, changes to fire regimes in heathlands, extensive drainage of wetlands, alteration to flooding regimes, and severe fragmentation of habitat are taking a heavy toll of the natural biota of this region. Of those temporary wetlands that have not been drained, many are now kept permanently flooded by landholders in order to attract waterfowl for hunting. On the other hand, despite several years of above average rainfall, Bool Lagoon has not filled since 1995. It is suspected that recent changes in agricultural practice, particularly laser leveling of fields, the widespread introduction of pivot irrigation, and rapid growth in the area under vines, may be inducing yet more changes in water regimes. The northwestern part of the region also has a severe dryland salinity problem, with an area of 2600 km2 affected in 1993, and increasing at an estimated 10 percent per year (Stove 1998).
Justification of Ecoregion Delineation
The Naracoorte Woodlands ecoregion consists of one IBRA, the ‘Naracoorte Coastal Plain’ region (Thackway and Cresswell 1995). This region is included in the larger ‘South-east Australia’ Endemic Bird Area (Stattersfield et al. 1998).
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Prepared by: Graeme T. Hastwell