The Botany of Iceland - 01.12.1930, Síða 56

H. M0LHOLM HANSEN
46
owing to the fact that polygon-formation and solifluction are be-
ginning to be prominent. The vegetation appears changed not only
because species already present occur with greater frequency but
also because new species have been added. The number of species
has almost been doubled, the density has increased from c. 2—4 to
c. 6—9. In table 10, 2—3 and 6—7 sliow the composition of the
species on older, more stable tracts of melar. The increase falls
especially to Ch. Of new species we may particularly mention Dryas
octopetala, Empetrum nigrum, Cassiope hgpnoides, Loiseleuria procnm-
bens, Luzula arcuata, and a number of mo plants. Dryas octopetala
only occurs in melar on Lýngdalsheiði, not, as is the case in the
highlands and the north country, in mo. The presence of Loiseleuria
and Cassiope would seem to show that the localities referred to not
only differ from the abovemenlioned in age but also by being more
snow-covered in winter.
On LSngdalsheiði the melar vegetation is not very widespread,
at any rate compared with the mo. In other parts of Iceland, how-
ever, it plays a prominent part in the physiognomy of the land-
scape, not only in the lowlands where it occurs in greatest quantity
near the sea, but also and especially in the highlands where the
country for miles is covered exclusively with the melar vegetation.
At the higher levels it is almost the sole prevailing vegetation.
The melar vegetation or fell field is an arctic type of vegetation
and has its greatest distribution north of Iceland, though it occurs
at high levels in the Faeroes, Scotland and Scandinavia.
In spite of the great physiognomic differences be-
tween the melar and the mosathembur vegetation, the
t w o t y p e s m u s t b e i n c 1 u d e d i n t h e s a m e c 1 a s s, c h a r a c -
terised witli regard to environment by not being covered
w i t h s n o w i n t h e w i n t e r a n d b i o 1 o g i c a 11 y b y t h e c o m p a r a-
tivelv great quantity of Ch and A species, especiallyA3
species. Both types have their main distribution in arc-
tic regions about, above, or north of the 20 p. c. Ch bio-
chore. The two types show a striking difference in re-
gard to their biological spectra, the melar vegetation
having a cornparatively high II percentage and a low
(’i percentage, the mosathembur vegetation a high (i per-
centage.