Náttúrufræðingurinn

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Náttúrufræðingurinn - 1964, Side 110

Náttúrufræðingurinn - 1964, Side 110
202 NÁTT Ú RU F RÆÐ IN G U RIN N S U M M A R Y Studies on the effect of grazing on the vegetation of a highland rangeland in South Iceland by Ingvi Þorsleinsson, The University Rcsearch Institute, Reykjavíh. The range management division of the University Research Institute has been working since 1955 on problems concerning the udlization of vegetation of the common rangelands in the highlands of Iceland. The main purpose of this work is to determine the carrying capacity of the range and to test methods of increasing the forage production. This work includes detailed mapping ol the highland vegetation. The present paper deals with a study of a common rangeland in South Iceland, wich was carried out in 1961 and 1962. This range has been protected from grazing for 15 years and was reopened to sheep in 1962. The purpose of this work is to study tlie effect of grazing on plant density, botanical com- position, forage production and root development. Plant density and botanical composition were measured by the line intercept and the point frame method, both methods being used wherever possible, but tlie latter method only where plant density was too high or the presence of liummocks prevented use of the line intercept method. These measurements were made on randomly selected sites and will be repeated every few years. Such quantitative plant measure- ments have been used very rarely in Iceland until now. Examples of the results are sliown in tables I, II and III. Detailed mapping of thc vegetation was performed with the aid of aerial pliotographs. Table IV shows the results of this mapping. The total size ol the land coverecl by vegetation is about 24.600 acres. This is close to 12 per cent of the total size of the range. The vegetation is classified into 31 plant societies. Of these tlie Rhacomitrium heath societies (Ai—A7) cover by far the largest area, as is usually thc case in the highlands of Iceland. It is pointed out, that a very small area is covered by plant societies dominated by plants, which are most palatable for sheep (grasses, dryland sedges and different herbs). No information is available to indicate whether the plant societies mapped represent climax vegetation. There is sorne reason to believe that the botanical composition of many of the dryland societies represents a stage of deterioration, caused by prolonged overgrazing. The results of measurements of the current production of 22 plant societies on the range in 196] and 1962 are shown in table V. Herbs and woody plants are weighed separately, as wmody plants are found to have very little grazing value in the summer, which is the time at which the highland ranges in Ice- land are used.
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