The Botany of Iceland - 01.12.1945, Page 89

THE VEGETATION OF CENTRAL ICELAND
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vegetation period is reduced, so that it will be too short for them.”
(translated from the Danish). Although my observations here are too
few to warrant perfectly valid conclusions, I should think that up to
an altitude of c. 650 m the snow-covering in the snow-patches will
further the growth of the southern species, if we are not concerned
with “extreme” snow-patches. Beyond this altitude the time which the
snow-patches will afford the plants for their growth is too short for the
southern species.
In the life-form spectrum similar fluctuations will be seen as in the
species group spectrum. Especially the Ch percentage is somewhat lower
than the A percentage except in group I, where the Ch percentage is
particularly high. The H percentage agrees fairly well with the flora
spectrum, but decreases considerably with the altitude. The geophytes
generally show much higher percentages in the snow-patch spectra
than in the flora spectrum, from which we might perhaps conclude
that the snow-patches afford comparatively favourable life conditions
to this life-form. The Th percentage is altogether lower in the snow-
patch spectra than in the flora spectra, but show no special tendency
to change with the altitude. It is fairly evident that the hemicrypto-
phytes decrease in the snow-patches with increasing altitude, and they
are likewise as a rule reduced in the “extreme” snow-patches. M 01-
holmHansen’s contention (1930, p. 154) that “... where the
snow-covering is deepest, H play the most pro-
minent par t”, accordingly only holds good until the snow-cover-
ing attains a certain duration. If this limit is exceeded, the hemicrypto-
phytes will be reduced, mostly for the benefit of the chamaephytes.
Below I have divided the snow-patch associations according to the
thickness of the snow-covering in the particular places into three groups.
As no measurements are at hand, this estimate of the depth of the
snow is, of course, based on a consideration of the terrain, but it is
hardly far out.
Group A: snow-covering scanty compared with other snow-patches,
Ass. 1, 2, 3, 8.
— B: snow-covering moderately thick compared with other snow-
patches, Ass. 4, 5, 7.
C: snow-covering thick compared with other snow-patches,
Ass. 6, 9, 10, 11.
Finally I mention the species occurring in the snow-patches in-
vestigated by me. I have arranged these species into two groups, of
which group I is divided into two subgroups.