Flóra: tímarit um íslenzka grasafræði - 01.06.1968, Síða 50

moss species around the spring and two of these streamlets which are
quite different, one having an influx of cold water too, in the spring.
The immediate vicinity of a hot spring and running hot water must
be a rather constant biotope throughout the year. The combination of
mosses found there may give information about the changeability of
the milieu if found elsewhere. The difference between the two stream-
lets shows well in the moss vegetation on the banks: the one witli only
hot water and a gradual decrease in water temperature is predominant-
ly bordered by Rhytidiadelphus squarrosus; the other with a repetedly
abrupt decrease in temperature is variable and has for example more
Philonotis spec., Webera albicans and Sphagnum on its banks.
After a stay of two months, in the lowland heath of Suður-Þingeyj-
arsýsla I travelled two months in other parts of the country, for pur-
poses of comparison. Tlie most striking tliing to see is the rather strange
dispersal pattern of Icelandic plant species which is also met within
the heath. Phyllodoce coerulea heatli can only be found in the Eyja-
fjarðar district; in the East there is everywhere Campanula rotundi-
folia and, in a lesser degree, Alchemilla faeroensis; in the North-west-
are always lycopodiae and often ferns in the heath vegetation; Calluna
vulgaris does not occur there (Flóra íslands), and Arctostaphylos and
Empetrum nigrum I found only on some lowland patches close to the
sea at Barðaströnd. As concerned the last named species it is difficult
to say whether it is common or not, for it is hardly possible to examine
every Empetrum closeiy, but the specimens I studied in many places
in the NW. all turned out to be E. hermaphroditum.
At first sight the heatli on mountain slopes does not appear as com-
plex as in the lowlands. There is a plain zonation, depending on alti-
tude as well as on edaphic and moisture factors. Above 450 m all kinds
of Salix herbacea communities; between 200 and 400 m a belt in which
Loiseleuria procumbens often dominates. On racky slopes Rhacomi-
trium; if a little more humus is formed tlien Loiseleuria procumbens,
Calluna vulgaris, Empetrum hermaphroditum and Vaccinium uligino-
sum appear in succession. Schematically I tried to reproduce this in
fig. 3.
The heath on tlie slopes differs from that of the lowlands in that
neither Arctostaphylos nor Empetrum nigrum are of any importance.
In the mosslayer one finds on the slopes more Pleurozium schreberi
and especially in the NW, there is often a complete undergrowth layer
of a Dicranum species. Lichens like Cetraria nivalis, Cetraria crispa,
48 Flóra - tímarit um íslenzka grasafræði