The Botany of Iceland - 01.12.1945, Blaðsíða 30

372
STEINDÓR STEINDÚRSSON
It will be seen from the tables that the annual mean temperature
is very low; according to “Veðráttan” it is negative in Möðru-
dalur, but slightly above zero (o.i°) at Grímsstaðir. The difference in
altitude of the two localities only amounts to c. 30 m, but nevertheless
the difference in temperature is almost 0.50. Hence it is quite probable
that the temperature is even lower farther towards the interior of
the country. Looking at the temperatures of the individual months
or seasons, we shall see at once that the difference is much greater
in the winter months than in the summer months, the winter being
relatively much colder in Möðrudalur than at Grímsstaðir. However,
in a comparison these figures should be accepted with some reservation,
since the registrations were not made during the same series of years,
and the five years for which the temperature of Grímsstaðir has been
computed were comparatively warm, so the difference is probably some-
what less than shown here.
Thus it will be seen that the vegetation in this part of the high-
land is favoured by a considerable warmth in the summer, but in
addition has to struggle against a rather severe cold in the winter. How-
ever, the mean temperature does not give a quite correct picture of the
conditions. The most accurate picture of the temperature conditions
and the period of the summer which the plants have at their disposal
may be gained from Table II. It will be seen that at Grímsstaðir the
only frost-free period occurs from June 23rd to August iöth. Farther
up in the highland this period is much shorter, probably not exceeding
some 20-30 days at an altitude of 500 m or more. This table also shows
the time when the growth begins and the length of the snow-free period,
according to observations made at Grímsstaðir. There can be no doubt
that at Brúaröræfi conditions are very like those in Möðrudalur except
that the temperature must be somewhat lower. I suppose that Snæfells-
and Lónsöræfi do not differ essentially from Brúaröræfi in regard to
temperature, at any rate not the regions around Snæfell.
As is well known, the mountain range on which the large glaciers
lie in many respects forms the boundary between the northern and the
southern parts of the country. As to the climate this is especially evident
in the precipitation, but the temperature, also, is as a rule higher in
the south than in the northern part of the country. Thus it seems
natural to assume that the areas investigated in the south country,
Landmannaafrjettur and Siðumannaafrjettur, have a higher tempera-
ture than Brúaröræfi, but since no registrations are available, I can-