The Botany of Iceland - 01.12.1945, Blaðsíða 63

THE VEGETATION OF CENTRAL ICELAND
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mannaafrjettur, where the association likewise occurs. Here both Equise-
tum palustre and Carex rigida are very conspicuous, so it would perhaps
be most correct to call it a variant rich in E. palustre. The moss vegeta-
tion is more prominent in this analysis than is usual in the jaðar vegeta-
tion. Where this association is found, the surface is either level or with
small knolls. Analysis 2 was taken in a typical jaðar area, whereas
analyses 3-4 are derived from the banks of small streams, analysis 3 is
from Þorlákslindir, and 4 from an islet in Amardalsá. Here the soil
is so damp that no actual xerophytic flora can gain ground, but still it
is too dry for the mýri vegetation to thrive there. The moisture condi-
tions are about the same as in the typical jaðar, which is manifested
in the composition of the vegetation. Molholm Hansen (1. c.
p. 111) makes a similar remark as to the vegetation on the banks of
rivulets. According to their relation to other formations as well as their
species composition and distribution this association and the two follow-
ing associations are the most ypical jaðar found in he area treated here.
3. Juncus balticus—Festuca rubra—Carex incurva-Ass.
(Tab. VII. A-B, 6).
No other dominants or conspicuous species than the character species
are found in this association. It differs from the preceding one by a
greater paucity of species, notably Salix glauca is much less frequent,
and the Ch percentage is accordingly much lower. The association is
distributed over the inner part of Arnardalur and occurs in Fagri-
dalur in connection with association 2. It is noteworthy that sand plants
such as Carex incurva, Agrostis alba, and in part Festuca rubra are very
conspicuous. In this association the geophytes attain their maximum
within the jaðar, whereas the chamaephytes have their minimum here.
Over a great part of Arnardalur depressions alternate with slightly
higher ridges and stretches of land, in some degree resembling the
ridge mýri on Síðumannaafrjettur. Salix heath occurs on the ridges
there, but in the depressions a Juncus balticus association is found,
either the jaðar association 2 or 3; thus association 3 is found in the
deepest and wettest portions of the depressions, association 2 in the
driest places. The soil is very sandy everywhere, and there is hardly any
continuous cover of vegetation. The Calamagrostis association 4 occurs
in the deepest depressions. In view of the prevailing conditions I should
think that we are here dealing with an area which is being converted
from mýri or flói into heath. Large sand-drift areas are found in the