Bioregions of the nt
Kerle, J. A.
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Technical Report LRD94100 Viewed at 07:02:32 on 18/02/2010 Page 19 of 275. STONY PLAINS (STP) This bioregion covers the arid stony silcrete tablelands and gibber and gypsUm plains with sparse low chenopod shrub lands on duplex soils and calcareous earths. It includes some small rocky outcrops, mesas and mound springs. It is crossed by several dry creek and river beds. Location and Area The region occupies the central section of the northern arid half of South Australia, a total area of 181,592 km2 Only the very northern tip extends into the Northern Territory around 135E (1707 km2, 0.9%). Climate (OodnadattalCharlotte Waters) Warm to hot in summer and cool to cold in winfer. Temperatures show considerable diurnal and seasonal variation. Rainfall is extremely low and unreliable and evaporation is very high throughout the year. Mean annual rainfall is about 125-150mm. There are no major mountain ranges to induce rainfall .. Geology, soils and topography The Stony Plains are part of the Lake Eyre Drainage Basin which is the modern surface of the Great Australian (or Eromanga) Artesian Basin. This basin first formed during the Jurassic period, around 160 million years ago and is the largest and lowest internal drainage system of the continent. Amongst the early sediments deposited were thick sand beds which are now the Artesian water-bearing aquifers. There are also fossil beds containing marine invertebrates and early vertebrates. In the last 60 million years sands and gravels have been laid down, warped and folded to produce the silcrete encrusted mesas and hills and the associated gibbers and screes. Opals were also formed as part of the silicification process and the folding produced the rock structures which' have trapped oil and gas produced by buried organic matter. The mound springs lie around the south-western edge of the artesian basin and occur where water forces its way to the surface through cracks along the rim. The limestone mounds form when minerals brought to the surface by the water are left behind after the water evaporates. Vegetation Total number of species known, rare and relict species, weeds. The region is floristically diverse with the predominant vegetation being chenopod shrub lands and grasslands. The plant communities vary with the landform - gibber plains, creekbeds and mound springs. The gibber plains are sparsely vegetated, mostly with chenopod shrubs (Atriplex and Maireana species) which may have an understorey of grasses and ephemeral forbs. In some seasons Swainsona grows and flowers prolifically. The gibber plains are dissected by watercourses which support the growth of larger trees and shrubs. River Red Gums (Eucalyptus camaldulensis) grow along the larger watercourses especially favouring the waterholes, but the Coolibahs (E. microtheca) are the most Bioregions of the NTDRAFTVersion 3 16 . Printed:March 25. 1996