5.1.2 Linear dunes co-dominant (north and east of Big Desert, south of Millewa)

5. North Western Dunefields and Plains (DP)
5.1 Calcareous dunefields

East-west dunes occupy on the average, almost half of the landscape in east-west belts crossing the northern and central parts of the Mallee. The belts occur along the northern edge of the Sunset Country, in the central Mallee extending from the South Australian border through Ouyen to the River Murray between Nyah West and Boundary Bend, and also to the east of the Big Desert stretching from Patchewollock to Lake Tyrrell. Stranded ridges are particularly prominent along this latter stretch. Boundaries are clear, except to unit 5.1.3. Usual dune dimensions are width 100 m, height 3-10 m and length 1-3 km. Dune crests are smooth and the southern slopes are relatively steep. Vegetation is mostly small mallee with spinifex understorey on the crests and mallee with a sparse ground layer on the lower slopes. Deep loose sands on the dunes are mostly reddish-yellow, sharply underlain by compact yellowish-red sandy loam to sandy clay loam.

Interdune swales characteristically have medium-textured Calcarosols with red brown sandy loam to loam surfaces and yellowish-red subsoils with abundant carbonates. In places, visible carbonates extend to the surface which is grey-brown, locally referred to as “limey soil”. Shallow loams on limestone frequently occur in the west. The original swale vegetation is mostly mallee with sparse understorey.

There are scattered areas, usually on higher ridges, which originally carried woodlands of Pine (Callitris preissii), Belah (Casuarina pauper) and Buloke (Allocasuarina luehmannii). The soils, both on dunes and swales are a rich red brown colour, and highly regarded for agriculture.

Most of the unit has been cleared for agriculture except the northernmost area in the Sunset Country. The dunes and swales have very different moisture and fertility regimes, posing problems in management. Erosion has been particularly severe on the dunes, sometimes exposing the hard, compact cores. Drift sand accumulates on the flanks of the dunes and to the east of obstructions such as fences and remnant trees. The extent of erosion has been greatly reduced, but it remains severe during recurrent droughts. The development of saline seeps in swales is also a problem, increasing towards the south as the rainfall increases. The problem is discussed in the next unit.

Sandy Calcarosol on upper slope of linear dune near Ouyen. Compact layer below 1 M is the remnant of an eroded older soil.

Calcarosol on interdune flat near Ouyen. Profile 50

Open mallee vegetation on interdune flat near Ouyen; site of profile 50

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