The Botany of Iceland - 01.12.1945, Blaðsíða 87

THE VEGETATION OF CENTRAL ICELAND
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crust crops out here and there. The snow-covering is very long-lasting,
and the soil damp. The association hardly occurs except in the im-
mediate neighbourhood either of a glacier or of a perennating snow-
drift, whence cold thaw-water may trickle all the summer and permeate
and cool the soil. It reminds one of the formation called Cerastium
trigynum herb field by Resvoll Holmsen and described by this
author from Norway from an altitude of c. 1400 m. It is no doubt the
least exacting of all the snow-patch associations. Nowhere in the snow-
patch are the arctic plants so abundantly represented, the A percentage
is 83. The high Th percentage of 6.9 might seem surprising; but in the
present analysis this is solely due to the presence of Koenigia, and ;t is
a manifestation of the modesty of this species as to both soil and heat
and of the short time the species requires in order to complete its
development.
Finally mention will be made of the relation of the snow-patch
associations to the altitude above the sea and the depth of the snow-
covering in general.
I have arranged the associations in groups according to their vertical
distribution, as they occur in the highland regions investigated by me.
However, the table thus prepared was computed on the basis of the
localities of the different analyses, though in this way I could not
entirely follow the individual associations. The altitudinal groups are
as follows:
I. 400-500 metres, ass. 2-3 and anal. XII. 1-2, 6.
II. 500-600 „ „ 8 „ „ XII. 4.
III. 600-650 „ „ 1, 4-5, 7.
IV. 650-700 „ „ 6, 9, 11.
The subjoined table shows the results of these computations. In
columns 5-7 the species-group and life-form spectra computed by
Molholm Hansen (1930, pp. 17 and 28) for 5: 4-500 m,
6: 5-600 m, and 7 : 6-700 m are given for comparison.
It will be seen that in this table I have computed the mean values
for some of the species groups and for the life-forms. Association 10
has been omitted, since it hardly belongs to the typical snow-patch
associations. The biological spectra show a difference according to the
altitudinal groups. In group I, 400-500 m, the E-groups are still in
the majority in the snow-patch spectrum, though it is distinctly in the