The Botany of Iceland - 01.12.1914, Síða 128

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THORODDSEN
lude of 600—800 metres, there are usuallv gravelly tracts with scat-
tered individuals of rocky-flat plants, such as Silene acaulis, S. ma-
ritima, Cerastium álpinnm, Luzula arcuata, Polygonum viviparum,
Armeria maritima, Ranunculus gtacialis, Saxifraga nivalis, S. oppo-
sitifolia and others. In small damp hollows where the snow persists
for a long time there is often a characteristic dense growth of Salix
herbacea, which almost entirely conceals the moss-covering of the
ground, together with Sibbatdia procumbens, Gnaphatium supinum,
Oxgria digyna and Polygonum viviparum; in some places these are
associated with several other plants. In other places there are small
patches of Grimmia-heaths with scattered specimens of Pedicularis
flammea or Cassiope hypnoides. Here and there streams and bogs
occur with Carex rigida, C. lagopina, C. rostrata, C. incurva and others,
but most often with Eriophornm angustifolium and E. Scheuchzeri.
As has been seen from the preceding notes on the vegetation of
the plateau it is not easy to determine the altitudes or upper limits
of the different plant-regions. Of the Scandinavian upper zones, the
region of conifers is entirely absent, but, on the other hand, we
may be justified in speaking of a birch-region, of an osier-willow
region, and perhaps a lichen- or moss-region, but these regions pass
into one another in many ways, and overlap. During the period
after the Ice Age (the Purpura-lapillus Period) when it was warmer
than it is now, the birch grew everywhere in the lowlands even
on the northernmost headlands, but it had already retired from the
latter at the time the first settlers came to the island, and since
then, as we have already seen, its distribution has been considerably
limited owing to the interference of man and sheep. The present
Polar limit of Betnla odorata in Iceland has not been fully investi-
gated, but judging from what I saw on my journeys it appears, on
the east coast, to extend across Vopnafjördur to the west coast of
Melrakkasljetta, across Axarfjördur and Skjálfandi to Eyjatjördur
near the mouth of the valley of Fnjóskadalur. The stretch of land
between Eyjafjördur and Hunaflói is now devoid of birch coppices,
although these occurred tliere in olden times; how far out they ex-
tended at that time upon the peninsulas between the fjords is not
known. From Hunaflói the northern limit of the birch extends from
Steingrimsfjördur to Isafjardardjup. This is, however, only quite a
provisional limit; the subject requires to be investigated more closely.
As regards the upper limit of the birch, it differs considerably
in different parts of the island; it extends highest in Thingeyjarsysla