The Botany of Iceland - 01.12.1930, Síða 129

STUDIES ON THE VEGETATION OF ICELAND
119
species is likewise less, 10.0 as against 14.3. The dominant or typi-
cal species are Salix glauca, S. herbacea, Sibbaldia procumbens, and
Gnaphalium supinum. Vaccinium uliginosum, Empetrum nigrum, and
Salix phglicifolia have entirely disappeared. Of more or less do-
minant species we may mention Equisetum arvense, Carex rigida,
Ðeschampsia ftexuosa, Agrostis canina, Festuca rubra, Rumex acetosa,
Viola palustris, Taraxacum and Leontodon.
Table 25 A, 5 shows the circling results for a smaller snow patch
having a northern exposure. In its broad features this locality
corresponds to the bottom vegetation of the large snow patches.
Floristically there is the difference that Vaccinium uliginosum and
Ernpetrum nigrum are present in the small snow patches, while
Sibbaldia procumbens and Gnaphalium supinum are only present in
the larger ones.
Just as, within the mýri formations, the flói forms the extreme
point in a sequence of changes conditioned by the length of the
period when the ground is covered with water and the depth ot
*he water-layer, so also, in the formations lying above the ground-
water, the geiri shows a succession of changes conditioned by the
length of time that the ground is covered with snow and the depth
°f the lajrer of snow. Passing from melar by way of the mo to
geiri, the depth and duration of the snow-covering increases more
and more. Melar is without snow or almost without snow through-
°ut the winter, the mo has the snow-covering normal to the area,
while the geiri is already covered at the first snowfall in the autumn,
retains a deep and constant snow-covering throughout the winter,
and only becomes bare again when the snow melts far on in the
spring.
Now these conditions have the following effect on the vegetation.
Where the snow-covering is sliglit, it consists principally of arctic
species and life-forms, whereas, where it is deep, it consists of
southern species and life-forms.
Thus melar has a Ch percentage of 52, an H percentage of
36, an A percentage of 81 and an A 3 percentage of 55. The E
percentage is 0.
The mo (the knolly mo) has a Ch percentage of 38, an H
percentage of 47, the A percentage is 71, the A3 percentage 39, and
the E 3 percentage 4.
The geiri (the Geranium silvaticum belt) has a Ch percentage