123 STUDIES IN APPLIED ECOLOGY. I. A STATISTICAL ANALYSIS OF REGENERATION FOLLOWING PROTECTION FROM GRAZING. By Ilma M. Pidgeon* and Eric Ashby. (From the Botany ScJiool, University of Sydney.) (Plates ii-iii; one Text-figure.) [Read 24th April, 1940.] Introduction. Ecology is concerned with the interaction of organism and environment. The common approach to ecological problems is to regard the organism as the dependent and the environment as the independent variable; this approach has led to some understanding of the effect of environment upon plant and animal communities. Some eighty-five per cent, of the area of New South Wales is under occupation. The effect on the vegetation of such changes in the habitat as man can make is therefore of great importance. In the United States the technique of the ecologist has profitably been applied to problems of land utilization; a similar opportunity to apply ecological technique exists here. The present paper initiates a series of studies in the effects of deliberate changes in the environment upon vegetation. For some years the country surrounding Broken Hill, New South Wales, has been very badly eroded as a result of timber cutting and heavy grazing by rabbits, goats and stock (Morris, 1939). In an endeavour to protect their new buildings from sand-drift, the management of the Zinc Corporation at Broken Hill fenced, in June-August 1936, about 22 acres on the south-west side of their works. After a few months, during which there were good falls of rain, the protection of this area led to the appearance of many grasses and native shrubs, although it had previously been practically bare. The contrast between the fenced area (now known as the Albert Morris Park) and the surrounding country was so marked that Mr. Albert Morris, at whose suggestion the area had been fenced, found support for a proposal he had advocated for many years: to arrest sand-drift by fencing a wide area round the outskirts of the town. He believed that fencing, by the exclusion of stock and rabbits, would permit the regeneration of the natural plant-cover. With the financial help of the North Broken Hill and Broken Hill South Mining Companies, Mr. A. J. Keast, manager of the Zinc Corporation, fenced about 3-5 square miles of country. The enclosed area lies as a semi-circle of nine paddocks on the southern and western outskirts of the town. The fences are of iron posts and 1-5-inch rabbit-proof netting and were erected during the period from July 1937 to February 1938. In March 1939 an additional area was fenced at the expense of the Government of New South Wales. The effect of fencing is most beneficial. Areas which previously were sparsely-populated sandy wastes are now occupied by a good cover of grasses and * Linnean Macleay Fellow of the Society in Botany.