The Botany of Iceland - 01.12.1945, Blaðsíða 92

434
STEINDÓR STEINDÓRSSON
Smith’s definition (1920, p. 29) : “Hithörande váxtsamhállen karak-
teriseras af, att fáltskikten i dominerande grad bestá af ris, xerofila grás
och halfgrás... Bottenskikt finnes vanligen och utgöres dá af lafvar och
mossor. Humusbildningen ár sárskilt inom den lafrika underserien
obetydlig.” (Plant communities belonging to this [series] are charact-
erised by the “herb layer” consisting predominantly of shrubs, xero-
philous grasses and Cyperáceae... A ground vegetation is usually
present, and if so, consists of lichens and mosses. The formation of
humus is inconsiderable especially within the lichenous subseries).
This definition fits the formation called heath in the present paper.
The only difference, I should think, is that in the heath in Iceland the
ground vegetation is often sparsely developed or not developed at all,
which, again, is due to the influence of the blown sand.
Of the formations mentioned so far the heath is the most widely
distributed within the areas investigated by me, but in this respect it
cannot compare with the fell-field. Heaths are met with wherever there
is a closed vegetation and the soil is so dry that the mýri series has been
unable to develop there and the snow-covering is of too short duration
to permit the development of a snow-patch vegetation. In depressions
and valleys the heath mostly forms belts along the base of the slopes,
and in the mýri or flói areas with higher-lying stretches, the latter are
covered with the heath vegetation. Next to the fell-field, the heath is
the formation which characterises the highland vegetation above a
height of c. 550 m. The heath may naturally be divided into two
subseries, the dwarf shrub heath and the Grimmia heath.
a. The D w ar f S h r u b H e at h.
Of the two subseries the dwarf shrub heath is the commonest and
most widely distributed within the regions investigated by me. It is
conspicuous almost wherever the soil is suitably dry, and its character
species, Salix glauca and S. herbacea, spread even far into the neigb-
bouring mýri associations; on the other hand, some of the species of
the mýri are found in the heath, for instance Calamagrostis neglecta.
Thus the limits between these two formations may be somewhat in-
distinct.
As mentioned above, the dwarf shrub heath is always the dominant
formation where the ground is somewhat elevated above the lowest-
lying parts of depressions and valleys. The surface of the heath may be
almost horizontal, but mostly it is somewhat inclined, though rarely
very much, for if so, the vegetation will pass either into the brekkur