The Botany of Iceland - 01.12.1930, Síða 152

142
H. M0LHOI.M HANSEN
Under Ihe treatment of the formations in the various localities
examined, the causes of tlie diíferences in vegetation have been more
precisely stated. At Bjork in the south country the diíference be-
tween the Elyna mo and the Arctostaphylos mo was caused, amongst
other things, by a difference in the depth of the snow-covering.
The Elyna mo has a relatively tliin covering of snow, that of the
Arctostaphylos mo is somewhat deeper. However, the diíference is
not considerable enough to cause the appearance of two different
types of vegegation. At Norðtunga in the south-west country mo
and forest-ground are covered by snow of different depths; while
the nio has the snow-covering normally occurring in that part of
the country, the forest-ground is covered by a considerable layer of
snow throughout the winter. At Lækjamót in the north countrv,
the mo has likewise the normal snow-covering, whereas the melar
is bare of snow. All these localities are lowland localities situated
at c. 50—100 m above sea-level. If we pass from the lowlands to
the highlands, the difference in the scale of snow-covering will be-
come increasingly evident. At Ljfngdalur in the south country
(c. 250 m above sea-level), three types of vegetation are easily
distinguished. The difference between these three types, inosathembur
and melar with little or no snow-covering, mo with a normal snow-
covering, and geiri with a deep and constant snow-covering, is due
to the diíference in the snow-covering. In some places a transitional
form between mo and mosathembur had developed, with an inter-
mediate depth of snow.
At Thrasaborgir (c. 400 m above sea-level) the three types
mosathembur, mo and geiri were likewise devoloped.
On Arnarvatnsheiði near Úlfsvatn at an altitude of c. 500 m
above sea-level, the scale of snow-covering was further differentiated.
The 5 types of vegetation, melar, Betula-nana mo, the knolly mo,
the sides of the snow patehes, and the bottoms and north sides of
the snow patches, represent 5 different degrees of snow-covering,
where the first type has the slightest snow-covering of the shortest
duration, the last, the deepest snow-covering of the longest duration,
Tahle 29 gives the distribution of the species in the scales ot
snow-covering of the 6 localities mentioned above. Within each
locality the formation most devoid of snow is given first, l'urthest
to the left, while the formation with the deepest snow-covering is
put last, furthest to the right. Bjork a is the Elyna mo, Bjork b