Greinar (Vísindafélag Íslendinga) - 01.01.1967, Blaðsíða 71

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It is also clear that the number of species increases rough-
ly in proportion to the area of the islands and the corre-
sponding variety of growth conditions (Table II). It must
be mentioned, however, that number of species and com-
position of associations are also affected by microclima-
tic factors, such as humidity, shelter and exposure. The
Angelica clusters constitute a localized association to the
northern side of the islands, where the sun is least effec-
tive and there is sufficient moisture. The dominant spe-
cies of this association is Archangelica officinalis, an arc-
tic species that flourishes in low temperatures but demands
a fairly large amount of moisture and a soil with a rather
high fertility content. Sheep are very partial to the An-
gelica and keep it down wherever they can get to it. For
this reason it is only found on cliff faces and in clefts
in the rock where it is hard to reach.
It can be regarded as certain that the grazing of sheep
has had a material effect on the vegetation of the islands,
both through their introduction of seeds and also by selec-
tive grazing, for example of the Angelica. With the single
exception of Ellidaey, the islands are now no longer used
for grazing, and this is bound to bring some changes in
the vegetation. The areas of vegetation on these islands
will thus tend to revert to their natural balance. Sheep,
when grazing, consume part of the annual growth which
would otherwise wilt. A great mass of wilted grass suffo-
cates the living, resulting in bare patches as observed in
Bjarnarey.
Differences between the islands in number of species
and associations have been discussed above with reference
to varying conditions of growth. It must, however, be
borne in mind that the dispersal routes to individual is-
lands vary in distance, and also that the period of time
elapsed since the formation of individual islands in the
group may vary considerably. Thus, Ellidaey is relatively
poor in species in view of its size and proximity to the
mainland, which might seem to indicate that it was of
comparatively more recent formation. Its dry meadow
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