Náttúrufræðingurinn - 1964, Blaðsíða 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.