The Botany of Iceland - 01.12.1930, Side 157

STUDIES ON THE VEGETATION OF ICELAND 147
I a, (mosathembur); from here its value decreases until it attains
its minimum together with the maximum of the E per-
centage in the class with the deepest snow-covering. The
proportion of the average F.-percentages of the two species groups
in the class most bare of snow is as 83 to 17, in the class with
the deepest snow-covering as 34 to 66.
The variations in the distribution of the individual sub-groups
are closely correlated to the variations in thp distribution of the
main groups. A 3 attains its highest value in the highest class and
thence the F'.-percentage decreases steadily as we pass downwards
through the classes. It shows the following change: 70 48 35 20.
The maximum of the A 2 species lies lower in the scale,
that of the A 1 species still lower.
The maximum of the latter group is in class II, corresponding
to the normal snow-covering of the country. In this class the E
species, too, attain their maximum, though not a very pronounced
one. The lower E sub-groups, E 3, E 2, and E 1 all have their
maxima in class III, corresponding to the fact that the species
thrive best where there is a deep and constant snow-covering
throughout the winter. Here E 3 is most abundant, E 2 is somewhat
less dominant, and E 1 occurs only sparsely.
Thus to the 3 classes of snow-covering there corresponds a
vegetation quite definitely stamped by its environment. In class I
it consists chiefly of A 3 species, less of A 2 species, in class II of
A 2, A 1, and E 4 species, and in class III of E 3, E 2, and
E 1 species.
The snow-barevegetation of Iceland thus consistsof
species with a pronounced northern distribution, the
vegetation with a constant snow-covering of species with
a pronounced southern distribution, and tlie vegetation
with a normal snow-covering is composed of species be-
longing to tracts the climate of which corresponds to
that of the country.
Conditions in the individual localities entirely confirm the facls
stated above, bolli in respect of the quantitative distribution in the
main groups and the position of the maximum in the individual
subgroups. A decrease in the amount of snow will always tend to
render the vegetation more arctic, an increase will render it more
southern.
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