The Botany of Iceland - 01.12.1945, Side 136

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STEINDÓR STEINDÓRSSON
is another one slightly higher
and drier than the first one.
(Fig. 16, 3). Here the sur-
face is usually knolly, and a
number of mosses occur in
the ground vegetation. It is
somewhat variable which
species dominate; in most
cases it will be Carices, often
mixed with Calamagrostis
and Salices. Sometimes pure
mýri associations are found
in this belt, but in other
cases it will be a mixture of
mýri and jaðar vegetations.
Where the pools lie close to
the hills (see Fig. 15), this
belt is mostly absent. The
third belt is the margin of
the rúst; it extends over the
slope of the rúst from the
surface of belt 3 to the edge of the top of the rúst (Fig.
16, A 4). The vegetation of this zone is generally a mixture of
jaðar and heath vegetations, though in most cases rather the lat-
ter. Salix glauca and S. herbacea often dominate in this zone,
but they are frequently mixed with Calamagrostis and Empetrum
nigrum, which may be very conspicuous. If the rústs are low, this vege-
tation is found all over the top of the rúst, or in other cases the vegeta-
tion of the top spreads across the edge of the rúst (Fig. 16 B and C).
The fourth belt is the top of the rúst (Fig. 16 A 5), which as a rule
forms a level or slightly rounded surface. The appearance and vegeta-
tion of the top may vary greatly. Often it has a larger or smaller
number of cracks, then the vegetation will generally be scattered,
presenting large open spaces, especially if the wind erosion has com-
menced to ravage the top, as is often the case. Sometimes the wind
erosion has played such great havoc on the top of the rúst that the
soil, gravel or sand, will be visible. In other cases the top is entirely
covered, and if so, by a heath vegetation. Thus all formations and
transitions from the flag to the Salix—Empetrum, or Grimmia heath may
be met with on the tops of the rústs. In certain cases such vigorous