The Botany of Iceland - 01.12.1945, Blaðsíða 134

476
STEINDÓR STEINDÓRSSON
present vegetation with that described by Thoroddsen in 1894
shows that a great change has taken place. Eriophorum and the Carices
then growing there had disappeared and had been replaced by a mix-
ture of the valllendi and the heath vegetation. This change has its
natural causes. In 1894 the advance of the glacier had, as it were,
just taken place. On the soil of which these folds are formed there grew
Eriophorum and Carices, as on the remaining part of Eyjabakkar.
During the short period that has elapsed since the advance of the
glacier the vegetaiion has not changed, as in addition it received suf-
ficient moisture from the glacier, which then lay quite close to the
terminal moraine. When subsequently the glacier receded, and the
terrain dried out, the mýri or flói vegetation was unable to hold its
own any longer, and the xerophytes invaded the moraine in its place.
However, so far none of these has actually gained the ground; its
vegetation is a mixture of different associations. In a few places in
the depressions, however, the mýri vegetation can be seen to hold its
own in the dampest soil. The biological spectra of the analyses show
a more marked arctic character than the morainic ridges themselves,
and the Ch percentage is likewise highest here, but otherwise there
is no noteworthy difference in the spectra.
The conclusions that can be drawn from these investigations of the
moraines are as follows: The terminal moraine harbours a luxuriant
and vigorous vegetation if it is made up of ancient soil besides the
material supplied by the glacier. This vegetation consists largely of
grasses and herbs. H is the dominant life-form, geophytes are fairly
abundant, while chamaephytes are of little importance. The southern
plant element is much more abundantly represented than is generally
the case in the highland vegetation. The pioneers on the ground moraine
are chiefly phanerophytes and almost exclusively arctic plants. These
are the more conspicuous the damper and more clayey the moraine is.
Geophytes hardly occur in the vegetation of the ground moraine, and
the proportion Ch: H is c. 3:7. According to my observations, it is
impossible to determine the age of the moraine on the basis of its vegeta-
tion.
7. THE FLA VEGETATION (TUNDRA MÝR)
One of the most characteristic plant communities occurring in the
highland of Iceland is the flá. However, it is no homogeneous forma-
tion like the other formations described here, but a complex of three