The Botany of Iceland - 01.12.1945, Blaðsíða 47

THE VEGETATION OF CENTRAL ICELAND
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mineral soil. The condition is that there is an afflux of fresh oxygenated
water). This can be distinctly observed in the Icelandic highland.
Wherever there is a supply of fresh water either from springs or from
rivers, Eriophorum Scheuchzeri associations are met with, precisely at
the boundary between the dry and the damp soil. They may also occur
in blown sand where the soil has become damp in some way or other
without a visible amount of surface water having been supplied. Thus
Eriophorum Scheuchzeri associations are very often pioneer associations
in the highland, whereas they hardly ever occur in the typical flói. In
these associations mosses are always lacking in the ground vegetation.
8. Carex Goodenoughii—Calamagrostis neglecta-A&s.
(Tab. III. A-B, 1-2).
Within the highland I only found this association in Fagridalur,
whereas it is not quite rare in the lowland, though as a rule it occurs
more frequently in the mýri than in the flói formation. It is not un-
common in the above-mentioned locality, though it does not cover very
large areas. It occurs under somewhat special conditions, which will be
explained here. The bottom of the valley slopes inconsiderably both
towards Fagradalsá, which flows through it, and towards Kreppa,
which runs in front of the mouth of the valley. At almost right angles
to the direction of inclination of the valley bottom there occur some
rows of knolls, which form almost continuous ridges, mostly, however,
they are somewhat arched. Water will gather behind these ridges,
especially in the spring, and where they are highest, small lakes will
form. In other places flói is found behind the ridges, either if the
ridges have not been so strongly developed that the accumulated water
behind them has prevented a continuous vegetation, or when lakelets
have later been filled up. These areas of flói will often be rather dry
in the latter part of the summer, they are all covered with the C.
Goodenoughii—Calamagrostis-a.ssociaúon and very much resemble ir-
rigated meadows in the lowland, where, for cultivation purposes, the
meadows are flooded by water in the spring, and later drained again.
If, for instance, dams are built across an Eriophorum flói, Eriophorum
will soon disappear, while Carex Goodenoughii will take its place. The
knolly ridges here serve as dams and afford similar conditions to the
vegetation to those mentioned above for the irrigated meadows. These
ridges are probably solifluction phenomena.