The Botany of Iceland - 01.12.1945, Side 75

THE VEGETATION OF CENTRAL ICELAND
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snow-covering must be regarded as impossible. The vegetation is more
xerophytic than is the case in both the snow-patch and the brekkur
vegetation. Festuca rubra predominates together with the character
species. In addition Cerastium alpinum and Agrostis canina are of
frequent occurrence. The biological spectrum is in good agreement
with association 2.
c. TheSnow-patch Vegetation.
Where the snow lingers long or the snow-covering is abnormally
thick, a plant community will arise which owes its existence to the snow
conditions. Unfortunately systematic investigations of snow-patches
with registrations of the thickness of the snow and the duration of the
snow-covering in certain localities have not yet been made in Iceland.
Still it is possible for a person acquainted with conditions in Iceland
to judge with a fair degree of certainty from the terrain whether the
snow-covering exceeds the normal. Thus I base my remarks on the
snow-covering in the different places in the highland on a comparison
with other known localities and on observations on the way in which
the snow will settle in certain terrains.
Dealing with the relation between the snow-covering and the vegeta-
tion two things must be taken into account, viz. the thickness and the dura-
tion of the snow-covering. As a rule it may be said that the thicker the
snow-covering, the longer will it persist, at any rate at the same altitude.
However, this is not absolutely certain, thus it depends largely on the
exposure when the snow will melt in the spring. If we consider the
influence of the snow-covering on the vegetation, it will be fairly evident
that where the snow-covering is thick and constant throughout the
winter, without, however, persisting so late in the spring that the
growth period of the plants is noticeably curtailed, the snow-covering
will promote the growth of the vegetation. In such places a particularly
vigorous vegetation will be found, usually very rich in species, at any
rate as compared with the immediate surroundings: southern species
are very conspicuous. However, it is not the snow-covering alone which
causes the good growth. It should not be forgotten that such places
are always sheltered and are, as a rule, so situated that the heat of
the sun may be fully utilised throughout the whole growth period.
Examples of that kind of snow-patches are to be found in luxuriant
herb fields or herb slopes and in Vaccinium slopes in the lower-lying
regions. Where, owing to the circumstances, the snow will persist till