The Botany of Iceland - 01.12.1930, Side 26

16
H. M0LHOLM HANSEN
lower and lower, while the winter grows colder and colder. At the
same time the flora shows a greater and greater paucity of species.
Unfortunately Stefánsson’s “Flóra íslands” gives no upper limit
for the individual species, and as far as Iceland is concerned, only
very few authors have stated at what altitudes they have found the
plants collected by them. Thoroddsen (1914) has given most in this
respect. By comparing what is found in the literature concerning
the occurrence of the plants in the highland tracts with my own
notes, but especially thanks to a long series of flora lists courteously
left at my disposal by Mr. Pálmi Hannesson, I have been able to
work out the biological spectra of the highland tracts of Iceland
given below, divided into zones of 100 m each, from 300 m to 1200 m,
the highest locality in which plants have been found.
While 375 species of vascular plants have been found in the
whole country, only 224 species have, up to the present, been found
above the 300 m curve, and only c. 100 species above the 600 m
curve. Going higher still, we find only 40 species above the 800 m
curve, and the number is further reduced when we reacli the snow-
line above which all higher plant life is excluded. It applies to
Iceland as to other arctic regions, the Faeroes, northern Norway
and Greenland, that only a limited number of species has any lower
limit, while most of the species decrease as we go upward and
sooner or Iater reach their upper limit. The following species are
of common occurrence right up to the snow-line: — Luzula arcuata,
Ehjmus arenarius, Poa i/Iauca, P. alpina, Festuca ovina, Salix glauca,
S. herbacea, Oxgria digyna, Cerastium alpinum, Silene acaulis, S. ma-
ritima, Ranunculus glacialis, Arabis petrœa, A. alpina, Empetrum ni-
grum, Saxifraga groenlandica, S. oppositifolia, S. nivalis, and Armeria
vulgaris. With few exceptions all the above-mentioned species are of
common occurrence in Greenland right up into the northern parts.
From considerations of space the species lists are not included.
The biological spectra calculated from them are given in table 3.
There is a diflerence in the occurrence of the individual life forms.
Some show a decrease as we go upwards, others increase, and others
again are constant. The H percentage is fairly constant through all
zones, c. 50. Pt, G, HH and Th decrease strongly as we go upward;
above the 800 m curve these types have only been noted a few
times. With respect to their content of these life forms, various
diflerences may be shown to exist between the various zones, and
possibly the highland tracts between 300 and 800 m may by means