The Botany of Iceland - 01.12.1942, Side 69

THE PTERIDOPHYTA AND SPERMATOPHYTA OF ICELAND
67
The Icelandic woods are in the main limited to the valleys of the
lowlands, often standing on thc lower parts of the mountain-slopes, in
sheltered places; very frequently the snow-layer covers the trees in the
winter, except for the taller individuals or the parts standing at some-
what higher levels.
c. Birch scrub. In many places which in former times carried
well-grown birch wood only more or less scattered scrub is now found
as relics. As previously mentioned, the reduction of the wood is mainly
due to the extensive use of wood for fuel, and also in some degree to
the ravages of sheep. Often the low and scattered growth of the birches
is due to the exposed situation, to unfavourable soil conditions and water
supply, etc. The birches in low-grown scrub frequently have very small
leaves, and hybrids between Betula þubescens and B. nana may possibly
occur. But since B. þubescens in Iceland is on the whole exceedingly
variable, it may often be very difficult to determine with any certainty
whether we have hybrids before us (H.J., 1900, p. 72). The height of
the birch scrub is as a rule from 1 to 2 m, and may sometimes be up
to 3 m. The lower parts of the trunks are more or less decumbent, and
often several branches arise from the same root.
d. The ground flora of the birch wood. According
to the nature of the locality, soil conditions, exposure, the more or less
dense growth of the birches, etc. the ground vegetation may differ
much with respect to number of species and composition. As typical
forest-ground plants may be mentioned the following (cp. also M.H.,
1930, p. 89—92; H.J., 1895 b, p. 25; Id., 1900, p. 75).
Fragaria vesca
Rubus saxatilis
Geum rivale
Prunella vulgaris
Trifolium repens
Geranium sylvaticum
Vaccinium Myrtillus
Arctostaphylos Uva-ursi
Calluna vulgaris
Morcover:
Deschampsia flexuosa
Anthoxanthum odoratum
Festuca rubra
Thalictrum alpinum
Carex rigida
Vaccinium uliginosum
Agrostis canina
„ tenuis
Galium boreale
„ pumilum
Polygonum viviparum
Empetrum nigrum coll.
In Hallormsstai'iaskógur, in birch-wood with Salix þhylicifolia and
Salix lanata, the following species were observed in the ground vegeta-
tion (1 .VIII. 1935) ;
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