The Botany of Iceland - 01.12.1930, Blaðsíða 57

STUDIES ON THE VEGETATION OF ICELAND
47
The Mo Vegetation. Figs. 6—7, table 11 A—B.
The mo is the type of vegetation Nvhich occupies the largest
area of Lýngdalsheiði as well as in the rest of the Icelandic low-
lands. The term mo as nsed here inclndes all such for-
m a t i o n s a s a r e n o r m a 11 y c o v e r e d w i t h s n o w i n t h e w i n-
ter, whose degree of moisture is exclusively determined
by the precipitation, not by the ground water, the soil
ofwhich is not in motion, uncultivated, and not covered
with forest or copsewood. Thus defined, mo comprises the
following of H. Jonsson’s formations: heath, heather mo, grass mo,
dwarf willow (in parl), and grass-íield (in part).
Tbe soil of the mo is always more or less covered with knolls
as shown in íig. 6. According to the inclination of the surface some
differences appear which do not, however, seem to be of great im-
portance in their bearing on the vegetation. Where the surface is
level or slightly inclined, the knolls are almost polygonal, half a
metre liigh and broad, and separated from each other by narrow
íurrows. Wliere the soil is more inclined, the knolls grow smaller
and arrange themselves in longitudinal rows parallel to the edge of
the slope. The form of the knoll undergoes a change, not only in
tliat il becomes more elongaled, but also because it begins to move
downwards. Tliis occurs bv a displacement of the material of the
knoll itself, apparent by its bulging in the middle of the more or
less vertical side facing the valley, and becoming flattened on the
upper side. Sometimes the upper side is bare, devoid of vegelation.
H all tbe knolls become flat and bare on the upper side, and out-
wardly delimited by a vegetation curve, we get typical solilluction,
which is especially well developed on melar in the highland tracts.
If the slope becomes still steeper, the solifluction will assume
fhe character of a landslip. Then it is no longer the single knolls
hut the substratum that slips, and in consequence the vegetable
covering may be preserved intact. Such landslips were observed in
the highest stage of development in thc highlands and the north
country.
Since the mo forms the bulk of the vegetalion as a feature of
the landscape, it is obvious tliat forins transitional between the mo
uud the other types of vegetation must occur. In table 11, Nos. 1—5
t'cpresenf the lypical mo, No. tí is a transitional form between mo
und mosathembur, No. 7 a transitional fonn between mo and jaðar,