The Botany of Iceland - 01.12.1945, Side 79

THE VEGETATION OF CENTRAL ICELAND
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vegetation then occurs mainly in that side of the ravine which is the
most sheltered or which has a southward exposure. Often the snow-
patches occur on terraces or in almost circular depressions in the moun-
tain sides, which are bounded upwards by a steep solifluction wall.
It almost looks as though the snow-patch has cut its way into the slope
(see Fig. 5). Snow-patches are often formed in the lower parts of and
at the foot of the mountain sides (cf. Fig. 6). On level land surfaces
or on plateaus snow-patches may form wherever there is a small hill
or knoll which affords sufficient shelter for the snow to settle there;
the hill will then generally be covered by a fell-field vegetation. As a
rule the snow-patches have a southward exposure; they may, how-
ever, face both eastward and westward, but very rarely towards the
north, at any rate in the northern part of the country.
The most important snow-patch associations investigated are:
1. Geranium silvaticum—Salix glauca-Ass. (Tab. X. A-B, 1-2).
This association is found here and there in snow-patches in the
highland where the soil is sufficiently damp and the snow-covering
not too persistent. It is found almost exclusively in snow-patches with
a southward exposure. In larger snow-patches it often forms a belt in
the upper part of the snow-patch; (cf. Molholm Hansen 1930,
p. 118), but in smaller depressions it covers the whole snow-patch.
As shown by the table, this association is very rich in species, and
herbs are very conspicuous physiognomically. Salix glauca is the only
shrub which exhibits a noteworthy frequency. In this association it at-
tains such a considerable size that we might speak of a Salix scrub. In
addition to Geranium the following species are dominants: Taraxacum
croceum?, Ranunculus acer, Polygonum viviparum, Thalictrum al-
pinum, Equisetum arvense, E. variegatum, Empetrum nigrum, Vac-
cinium uliginosum, Erigeron borealis, Gnaphalium supinum, Festuca
rubra, Veronica alpina, Deschampsia flexuosa, and Bartschia alpina;
sometimes Habenaria viricfis, also, is very frequent. The percentage of
southem species is high, though the A-groups are in the majority.
H is the dominant life-form. The Ch percentage varies slightly, it
being the nature of the snow-patch associations rich in species that
the composition of the species may vary somewhat, though the
character species and the dominants are the same and are present in
the same quantities. The analyses from this association show relatively
good agreement with Molholm Hansen’s results from “the Ge-