The Botany of Iceland - 01.12.1945, Blaðsíða 52

394
STEINDÓR STEINDÓRSSON
dominating life-form, but the HH percentage is relatively high, which
points in the direction of the flói. The A percentage is much higher
than generally in the flói, but is in good agreement with the most
closely related mýri associations. Analysis 7 differs from the others in
that one of the character species is lacking, viz. Eriophorum Scheuch-
zeri, and it should accordingly be regarded as a variant. However, the
analysis was made in such immediate proximity to analysis 5 that I was
unable to discover any difference in the life conditions with the excep-
tion of a small difference in height. The mýri area in which these
analyses were made consists of depressions alternating with low knolls
or ridges. E. Scheuchzeri disappears along the margins of these ridges,
while the other species of the depressions hold their own. Where the
ridges are highest, there is a pure jaðar vegetation with predominant
Calamagrostis and Salix herbacea. The altitudinal difference between
the places in which analyses 5 and 7 were made does not exceed 20 cm,
but as to the greater number of sample plots it is even less, c. 10 cm.
This slight difference, which nevertheless seems to cause the consider-
able change in the species composition of the association, shows, per-
haps, most distinctly the struggle fought out here between the individual
species and associations. Porsild (1902, pp. 167-170) records a
similar case from the island of Disko, namely that the Cyperaceae
meadow is transformed into a heath because sand is carried down into
the beds of the rivulets so that they are dried out. However, in regard
to species composition and origin, the Cyperaceae meadow described by
him is closely related to the flói and mýri associations rich in Eriopho-
rum Scheuchzeri described here.
2. Carex rostrata—C. rarijlora—Salix glauca-Ass.
(Tab. V. A-B, 4).
Besides the three character species, Carex rigida and Polygonum
viviparum are frequent, but are not very prominent physiognomically
or in regard to degree of covering. I did not encounter this association
within my area of investigation except in Víðidalur, where it forms
small patches on the mountain sides. The analysis was made in such a
patch at an altitude of about 470 m. The composition of the association
is very similar to that of the lowland mýri. There is a rich moss vegeta-
tion, Philonotis fontana being especially abundant, which is connected
with the occurrence of a Philonotis-dý in the middle of the patch. The
H percentage is noticeably high.