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Bioregions of the nt



Bioregions of the nt


Kerle, J. A.


E-Publications; E-Books; PublicationNT; 176




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Technical Report LRD94100 Viewed at 07:02:32 on 18/02/2010 Page 22 of 275. MACDONNELL RANGES (MAC) Central Australia is dominated by sandstone and quartzite ranges varying in geological age and structure. It is a high, comparatively well watered and well vegetated tract of land. There are numerous spectacular gaps and gorges, often with permanent waterholes and the taUest'peaks in the N.T.; Mt Sonder, Mt Leibig and Mt Zeil, occur there. These ranges contain a high plant species diversity with 65% (1300) of Central Australian species growing there. The gaps and gorges are especially important in that they provide a wetter microclimate which allows relict plant species to persist and some annuals to survive severe droughts. Location and Area The MacDonnell Ranges bioregion covers the uplands,. east, west and south west of Alice Springs from 23S to 2430'S and 131 "20'E to 13530'E (36,986 km2). It includes the Heavitree, . Chewings, Gardner, James, George Gill, MacDonnell, Fergusson and Ooramrnia Ranges as well as other smaller outliers. With Alice Springs and several outlying communities it contains the highest population in Central Australia. Climate The arid climate of this region is ameliorated by the presence of the mountain ranges. Rainfall is greater amongst the ranges where temperatures and the evaporation rate are lower, especially within the protected valleys and gorges. In Alice Springs at the centre of the bioregion, weather data were collected at the Alice Springs Post Office from 1874 to 1988 and at the Airport from 1944. The mean town rainfall at 285mm is sig~ificantly higher than the Airport 10km south of the ranges (265mm) for the same time period. Most rain falls in swnmer when the monsoonal depressions can bring widespread rainfall or convectional thunderstorms produce highly localized storms. Mean temperatures range from 36"C (max)to 21C (min) in January and 19C (max) to 4 (min) in July .. Diurnal and seasonal temperature changes are large because of the extremely high levels of radiation, low humidity and little cloud cover. Frosts are common during winter with temperatures as low as -10C having been recorded. Potential evaporation rate is 3000mm per year. Geology, topography and soils. The bioregion is made up of two connected sections - a lobe to the north-east of Alice Springs and another to the south-west. It incorporates parts of two major geological units, the Amadeus Basin and the Arunta Inlier. The Amadeus Basin, an area of sedimentary accumulation (600-200 million years ago) is the predominant underlying formation south of Alice Springs, while the metamorphic rocks of the Arunta Block underlie a vast area north and north-west of Alice Springs. The mountain building event which produced the ranges of the MacDonnell Bioregion, the Alice Springs Orogeny, occurred 350-300 million years ago. As a result of this event along the boundary of these two geological regions the bioregion can be divided into two landforrn units: the crystalline ranges (Arunta metamorphics and granites) incorporate the northern and northeastern ranges (Chewings and Harts Ranges); and the folded quartzite and sandstone ranges Bioregions of the NT DRAFT Version 3 19 Printed:March 25. 1996

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