The Botany of Iceland - 01.12.1945, Side 71

THE VEGETATION OF CENTRAL ICELAND
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brekkur vegetation is a formation which is distributed not only in
Iceland, but also in Greenland, Scandinavia, and on the Faroes. How-
ever, according to the situation we may speak of lowland forms and
alpine forms.
The distribution of this formation in the area investigated by me
is as follows: On Landmannaafrjettur it attains by far its most ex-
tensive distribution, occurring all over the lower parts of the mountain
sides, especially on the slopes with a southern and eastern exposure. It is
also found on the slopes with a western exposure, but is less developed
there, and occasionally it occurs on the north-facing mountain sides,
but in such localities it does not extend as far up as in the other places.
The formation passes upward into the Grimmia heath or, where the
snow-covering is more long-lasting, into the Anthelia crust. On Síðu-
mannaafrjettur it is likewise of common occurrence, and in the lowland
tracts of southern Iceland the grassy slopes constitute the predominant
formation on all slopes and precipices. It was not found on Brúaröræfi
except very sparsely in Kringilsárrani and possibly in Fagridalur. The
mountains in this region have either bare sides or scattered snow-patches
separated by stretches of fell-field. The conditions on Snæfellsöræfi
are similar to these, whereas in Víðidalur í Lón the formation is fre-
quent but rarely extends above 600 m above sea-level.
It is not easy to discover the causes of this distribution. Already
Thoroddsen noticed the extensive distribution of the grassy slopes
in southern Iceland and connected it with the tuff formation; he says,
however, as follows (1914, p. 336) : “In other parts of the country
where basalt is dominant the grass vegetation of the mountain-slopes
consists of similar species, but is not so luxuriant as in South-Iceland.”
I suppose that the rock as such is not the main cause of the develop-
ment of the grassy slopes in the southern part of the country. It is
true that the deeper soil of the tuff regions may be one of the factors
which condition the formation of the grassy slopes, but if this were the
main cause, the grassy slopes would be just as widely distributed in
the tuff regions of the northern part of the country, which is not the
case. I am more inclined to think that the development of the grassy
slopes in the south is due to climatic conditions. In the northern regions
the climate is drier than in the southern tracts, and shrub heaths are
mainly met with in localities corresponding to those covered by grass
in the southern part of the country; but the shrub heath is a more
xerophytic formation than the grassy slopes. Possibly other factors, also,