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Water Stress On Native Vegetation During The Drought Of 1965

EW Pook, AB Costin, cWE Moore

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During the first half of 1965 an unprecedented drought caused widespread wilting of native trees from southern Queensland to the New South Wales-Victorian border. The reaction of some of the native vegetation in parts of the Australian Capital Territory and Monaro Region has been studied. Rainfall from January 1 to June 30 was less than one-quarter of the normal, and by the end of March signs of water stress were apparent over a wide area. The communities most severely affected were dry sclerophyll forests, especially on shallow, stony soils on northerly and westerly aspects. The ability of Eucalyptus spp. to withstand sustained severe dehydration is shown by the fact that the relative moisture content of living leaves could be reduced to 40-45 %, and maintained at these levels for long periods. The prolonged period of dehydration caused general drying out of the trees, rather than leaf and twig desiccation only. In the most severe cases, shrinkage and fissuring of the bark of E. rossii, with ultimate separation at the cambium, was observed. It is suggested that so-called ineffective summer rain in south-eastern Australia is both effective and essential for the native communities on soils of low water-holding capacity. The role of drought in the distribution of native communities is discussed.