The Botany of Iceland - 01.12.1914, Side 113

PHYSICAL GEOGRAPHY
297
Lastly some 40—50 foreign species have been found which have
not yet gained a permanent footing in the llora, some of which will
probahly again disappear.
There can be no doubt that the vegetation has been modified
in various wrays since man with his cattle-rearing came upon the
scene; sheep have especially exerted a great influence upon the
coppice-woods and other vegetation; in the few places to which
sheep cannot gain access, e. g. in distant valleys surrounded by
glaciers and rivers of great volume, on islands in the middle of
waterfalis or torrential rivers or in lakes the vegetation is usually
far more luxuriant than in other places. In Viðidalur in Lón I had
the opportunity of noting an example of the change effected by sheep-
rearing. The locality in question is situated 439 metres above sea-
level and has a southern exposure; it is surrounded by glaciers and
deep river-gorges impossible for sheep and cattle to cross. Formerly
the valley had been inhabited for a short time, but in 1840 it was
deserted by the inhabitants. I visited the valley in the cold summer
of 1882 and found there a very luxuriant vegetation; all the plants
had a height quite unusual in Iceland. At the bottom of the valley
tlie grass and the different species of willow' usually reached to the
horse’s belly; especially were Salix phijlicifolia, Geranium silvaticum,
ISartsia alpina and Archangelica officinalis of considerable size; there
was almost a wood of Archangelica which reached a height of 1 —
2 metres. The old ruins of the huts which were destroyed in 1840
by an avalanche were overgrown with Archangelica officinalis and
Salix phglicifolia, and from the old íire-place a willow', belonging
to the latter species, had growm out, about 2 metres in height, wúth
stem 3—4 cm. in diameter. In 1883 the valley wTas again inhabited.
I revisited the place in the summer of 1894 and found the condi-
tions greatly changed owTing to cultivation and the influence of sheep
and cattle. Tliat tract of land upon which the above-mentioned
species had reached their highest development was nowT laid out
as a manured home-field (tun), overgrowrn by species of grass cha-
racteristic of manured fields. These grasses had not, however, yet
gained mastery over the wúld vegetation; the single plants of grass
stood far apart, so that the field only yielded 64 cwTt. hay per annum,
wThile in the coastal districts a well cullivated field of the same size
would have yielded 240 cwt. Besides, the soil wras quite intersected
by subterranean portions of former plants, roots of willows, etc.
This vegetation would therefore in all probability quickly become