Náttúrufræðingurinn - 1984, Blaðsíða 46

record is regarded as 1% cover. Measure-
ments were made in a total of 87 quadrats
on the transects.
In order to include as many effects of
the topography on the vegetation as possi-
ble, the transects were laid over different
parts of the islet. Transect I crosses the
highest part of the ridge, where a thick
moss carpet dominated by Racomitirum
lanuginosum, covers the top (Fig. 3).
Transect II lies a little further north where
the upper part of the ridge is very hum-
mocky (Fig. 4). Transect III lies over the
narrowest northern part of the islet, where
the top has been eroded (Fig. 5). Transects
IV and V run from the east side of the lake
up to a nearby hill top, which has also been
eroded (Fig. 6 and 7). Transects IV and V
are assumed to be comparable to the west-
ern parts of transects I, II and III. Apart
from the vegetation measurements, some
soil samples from the transects were analy-
zed for water content (Table IV), pH,
organic matter and nitrogen (Table V).
On comparing the islet and the grazed
surroundings three different topographical
zones may be distinguished: west slopes,
relatively sheltered from prevailing winds,
the edges of the hillsides facing west, and
the ridge and tops of the hills. The main
results are the following:
1. On the islet there are higher values of
percentage cover of vegetation than in
the surrounding areas and stratification
of the vegetation is more pronounced
(Fig. 12). This is most clearly demons-
trated on the west slope where the
vegetation is dominated by 50-60 cm
high Salix phylicifolia shrubs and Gera-
nium sylvaticum and other herbs.
2. The composition of species is different.
On the islet the percentage cover
values are higher for shrubs (especially
on the west slope and the ridge edge).
broad leaved dicotyledons (esp. on the
west slope), mosses and lichenes (esp.
on the top) than in the surrounding
areas (Fig. 8, 9, 10, 11 and Table III).
In general the percentage cover values
are higher for species palatable to sum-
mer grazing sheep (Ingvi Þorsteinsson
1980b) on the islet, especially on the
west slope.
3. The grazed areas have generally a
higher number of species than the islet
but only few of them have great cover
(Table II).
4. There is significantly more litter on the
islet than in the grazed areas, especially
on the west slope (Table III).
5. The greatest vegetational difference
between ungrazed and grazed areas is
observed where conditions are most fa-
vorable for the plants, i. e. on eth west
slopes.
6. The soil has in general higher moisture
(Table IV), higher contents of organic
matter and is more acid (Table V) on
the islet than in corresponding zones in
the surroundings.
These results confirm in main aspects
results of other workers on the effects of
grazing on vegetation (Steen 1958, Ellison
1960, Ingvi Þorsteinsson & Gunnar Ólafs-
son 1967, Ingvi Þorsteinsson 1972 &
1980b, Wilegolaski 1975, ÁgústH. Bjarna-
son 1979). They do also support Höröur
Kristinsson’s (1979) suggestion regarding
vegetational changes on the Auðkúluheiði
heathland. It is concluded that the vegeta-
tion on the islet in the Lómatjarnir lake-
gives indications about the natural vegeta-
tion of the Auðkúluheiði heathland.
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