The Botany of Iceland - 01.12.1945, Síða 108

45°
STEINDÓR STEINDÓRSSON
b. The G r i m m i a h e a t h (mosaþemba).
As stated above, the Grimmia heath is of much more limited dis-
tribution in the areas investigated than the shrub heath. The main
character of this formation is that the phanerogamous vegetation is
scattered and the surface is mostly covered with mosses, especially
Grimmia hypnoides, which gives the formation its character. The Grirn-
mia heath is found both at high and low levels. In the highland re-
gions investigated it often extends to such great altitudes that it is
only surpassed in altitude by the fell-field and occasional snow-patches,
but, as is well known, it also occurs in the lowland right down to sea-
level. In the palagonitic regions the uppermost mountain peaks are
often covered with Grimmia heath, while the mountain sides are cov-
ered with the brekkur formation and the plateau is perhaps a barren
fell-field devastated by drifting sand. The most frequent phanerogams
in the Grimmia heath are: Salix herbacea, Polygonum viviparum, and
Carex rigida, furthermore Festuca rubra, Silene acaulis, Cerastium
alpinum, and Euphrasia latifolia. The A percentage is very high, and
almost exclusively species of the northernmost groups A3 and A2 are
represented. Of the life-forms, Ch shows the highest percentage, H and
G vary somewhat, as a rule, however, the G percentage is the highest in
the C. rigida association.
As mentioned above, the Grimmia heath as a rule occurs at high
levels within the areas investigated; thus on the south-facing side of the
mountain Loðmundur the boundary between the brekkur vegetation
and the Grimmia heath was found at an altitude of c. 800 m, in de-
pressions up to 850 m but on the ridges only up to c. 750 m. In places
with a thick snow-covering the Grimmia heath apparently attains no
great development. In other places, thus on Landmannaafrjettur,
Grimmia heath occurred under similar conditions to those on Loð-
mundur, but it was only sparsely developed on the north-facing moun-
tain sides, where it was often replaced by an association rich in An-
thelia, probably a kind of snow-patch association, in which, however,
essentially the same phanerogams as in the Grimmia heath are found.
On Landmannaafrjettur the Grimmia heath is present on the upper
mountain sides and on mountain tops, but no distinct boundary line
could be drawn between it and the fell-field vegetation. As a rule, how-
ever, the melar vegetation of the fell-field (i. e. the fell-field vegetation)
is found in the most exposed places, while the Grimmia heath occurs
in more sheltered places. On Brúaröræfi I observed Grimmia heath in