The Botany of Iceland - 01.12.1945, Síða 150

492
STEINDÓR STEINDÓRSSON
there the rúst is only found near the brook, where the soil is moderately
damp.
Point 4, the formation of ice in the rústs, has been dealt with
above.
I can say nothing about the relation between rústs and knolls
(Point 5), as I have made no observations in this respect. H a n n e s-
s o n’s statement regarding the connection between the development of
the flá and the temperature of the year is doubtless correct and in
full agreement with observations on the formation of tundra in other
countries. Thus F r i e s states that the annual temperature of northern
Sweden, where the formation of “Palsen” takes place, ranges between
— i.2° and — 3.2°C. Kihlman gives the annual temperature of
Orlow in Russian Lappland as — 2.4°C, and finally, according to
P o h 1 e, the annual temperature of Kanin ranges from o° to —4°C.
All these places have a low precipitation. Comparing these figures with
those recorded above from Möðrudalur, which give a fairly correct
picture of the annual mean temperature in the interior of Iceland, we
shall see that there is no great difference. In Möðrudalur the annual
mean temperature is —■ o.2°C, and farther towards the interior of the
highland it is no doubt somewhat lower. In my opinion it is remarkable,
also, that the formation of flá is very inconsiderable in those parts of
the highland which have abundant precipitation. It is most widely
distributed in the northern parts of the highland, where the precipita-
tion is lowest.
According to the observations recorded above I think that in regard
to the vegetation the main features of the development and distribution
of the flá as well as its nature may be summed up in the following
points. As will be seen, I here chiefly draw support from H a n n e s-
s o n’s statements.
1) Flá is only formed where the annual mean temperature is below
o°C.
2) In Iceland the flá is only found in the interior of the country and
chiefly between 400 and 600 m altitude. It may, however, be met
with at higher levels, right up to 700 m. The flá is far more widely
distributed in the northern parts of the highland than in he southern
parts, which is probably due to the lower precipitation in these
regions.
3) Flá is almost exclusively formed on level ground; only exceptionally
is it found on sloping ground. It will only develop in places which
are comparatively free from snow.