The Botany of Iceland - 01.12.1945, Blaðsíða 103

THE VEGETATION OF CENTRAL ICELAND
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absence of Empetrum, especially since Elyna Bellardi is often very
conspicuous in that association, where, however, it never dominates
physiognomically as here. The analysis was made on a small islet in
Arnardalsá. This holm is high in the middle and forms a low hill, on
which the analysis was made. The jaðar analysis Tab. VII, 6 was
made on the shore of the same holm. The locality exhibits a quite dif-
ferent physiognomy from that of the shrub heath in the neighbourhood.
Salix phylicifolia shrubs 50-75 cm tall grow here and there, but among
them the S. glauca—.E/jwa-association is found. It is noteworthy, also,
that this analysis is very rich in species, exhibiting 27 species, which is
the maximum of the shrub heath. The vegetation is much denser and
more vigorous in this small holm than is otherwise the case in Arnar-
dalur; I am inclined to think that it was a kind of relic vegetation
from the time the valley was much more luxuriant than it is at present.
The vegetation of the remaining part of he valley has been destroyed
by blown sand and wind erosion, notably after the immense eruption
of Dyngjufjöll in 1875, when large masses of volcanic ashes and pumice
were poured out over the valley. The river which encloses the holm
has protected it against erosion by the wind, and on account of the
terrain the volcanic ashes have been blown away from it so that its
vegetation has been able to hold its own in spite of the destruction of
the remaining part of the valley. This association is closely allied to
the Salix phylicifolia—Festuca-association, which is found under similar
conditions.
6. Salix glauca—Carex rigida--Ass.
(Tab. XV. A-B, 7-9; XVI. A-B, 1-4).
The analyses from this association are not entirely uniform, but
still have so much in common that I regard it as quite justifiable to
mention them as representatives of the same association. Wherever
these analyses were taken, the two character species S. glauca and
C. rigida dominated, although the latter has been somewhat suppressed
in two localities, but in these localities it still showed a considerable
degree of covering. In addition to those mentioned, the following species
are dominants in this association, viz. Equisetum arvense, E. varie-
gatum, Festuca rubra, Polygonum viviparum, Calamagrostis neglecta,
and Salix lanata. The association is found on rather damp soil, and
mosses are abundant in the ground vegetation; it resembles the jaðar
formation in several respects. Its occurrence would seem to show that
it is conditioned either by a damp soil or abundant precipitation. It is