The Botany of Iceland - 01.12.1949, Side 13

THE FLORA OF REYKJANES PENINSULA I i
their sheep destroyed this equilibrium of the vegetation
cover, and this is the real cause of the catastrophic loess deflation. The
same may be seen e. g. in Dalmatia or in North America. The
equilibrium can be restored only by excluding sheep grazing from some
districts for several years; in this manner the birch copses may
regenerate and extend their area, protecting the loess cover from defla-
tion and even accumulating new loess. In such recovered districts
grazing may be allowed for a certain period of years without any
greater danger to the vegetation while another district may be relieved
of the sheep and given its chance to regenerate.
The Vegetation.
From my plant-sociological studies of the area in question I have
arrived at the following results:
The most common community of the area investigated is the Rha-
comitrium lanuginosum heath. It is either an initial community on lava
fields or originates from the “fell-field” vegetation of Armerieto-Silene-
tum acaulis, where Ameria maritima, Thymus, Silene acaulis, Cerastium
alpinum, Cardaminopsis hispida and other flowering plants are do-
minating. Rhacomitrium lanuginosum is from the first very scattered
in this community, but becomes later on dominating. In the lowland the
Rhacomitrium heath includes a considerable number of higher plants as
Empetrum, Festuca vivipara, Thalictrum alpinum, Thymus etc. (Em-
petreto-Rhacomitrietum lanuginosi). In the highlands the phanerogam
component of the vegetation becomes more scattered containing only
such plants as Salix herbacea, Carex Bigelowii, Luzula spicata, Juncus
trifidus etc. It is the Rhacomitrietum lanuginosi islandicum. When the
soil cover is thick enough the frequency of flowering plants in the
Rhacomitrium heath increases, especially of Empetrum, Thymus and
Festuca vivipara, until a new community is established: Empetretum
nigri islandicum. The next step in the succession of the plant com-
munities is the Calluna heath (Callunetum islandicum) with Calluna,
Vaccinium uliginosum, Empetrum, sometimes also Arctostaphylos Uva-
ursi, Luzula multiflora etc. The climax community is the Hylocomio-
Betuletum pubescentis, where Betula, Hylocomium splendens, H.
'quarrosum, H. triquetrum, Rubus saxatilis, Galium boreale, and Vac-
cinium uliginosum are leading species.
Bog communities are dominated chiefly by Cyperaceae and by
mosses. The most common plant communities of the Reykjanes Penin-