The Botany of Iceland - 01.12.1930, Síða 151
STUDIES ON THE VEGETATION OF ICELAND
141
Equisetum variegatum and very high for Polygonum viviparum, corre-
sponding to a dense growth of Polggonum viviparum, a somewhat
more scattered growth of Equisetum variegatum, and a verv scattered
growlh of Poa alpina.
C. A third series is represented by Cardamine pratensis, Deschampsia
cœspitosa, and Carex capitata. These species all have their maxiníum
frequency percentage in class IV; they differ from each other in the
magnitude of the F.-percentage. For Cardamine pratensis the F
percentage is 59, for Deschampsia cœspitosa it is 41, and for Carex
capitata 8. Tliey also differ in the number of classes over which
they are distributed: Cardamine pratensis occui's in all classes of
moisture, I—VII, Deschampsia cœspitosa in classes II—V, and Carex
capitata only in class IV.
D. Most Icelandic species show the above-mentioned regular dis-
tribution in the scale of moisture. A small number of species deviate in
that they have two maxima with an intermediate relative minimum.
These species are represented by Empetrum nigrum, Vaccinium
nliginosum, and Betula nana. In a previous section on the distribu-
tion of the chamaephytes in the scale of moisture we attempted to
explain these facts. The relative minimum is due to annual varia-
tions in the water level.
Scale of Snow-Covering. Distribution of Species,
Species-Groups, and Life-Forms in the Same.
For the present it is not possible to set up a scale of snow-
covering as minutely graduated as the scale of moisture. The reason
is that so far the depth and duration of the snow-covering have
not been investigated. In the individual localities it is easy enough
to observe the etfect on the vegetation of the different depths of the
snow-eovering, but comparisons between the various localities are
rendered difficult by the fact that we have no exact particulars on
which to base a comparison betwTeen the scales of snow-covering
of the different tocatities. According to Thoroddsen (1914) the
snow lies longer and is of greater depth in the north country tlian
in the south-west, and in the south country there may be no snow
at all during a long period. In the highland tracts the depth and
duration of the snow-covering is greater than in the lowlands. These
facts must be taken into consideration in a comparison between
the differences in vegetation at the various stations.