The Botany of Iceland - 01.12.1945, Qupperneq 148

49°
STEINDÓR STEINDÓRSSON
and melur association 6, but it is poorer in species than these
formations.
5) The Empetrum nigrum—Salix herbacea-association corresponds to
shrub heath association 4; there is, however, the difference that in
the shrub heath S. glauca is always the dominant species, while
S. herbacea is more variable in the different localities, but in this
flá association the conditions are reversed. In series 8 this associa-
tion is actually the Saiix herbacea—Carex rigida-associa.úon of the
Grimmia heath.
6) The Salix glauca—Carex ngzcúz-association agrees with shrub heath
ass. 6.
It will be seen from this survey that belt 1 is a flói formation, belt 2
is a mixture of this and the mýri formation, though most nearly allied
to the latter, belt 3 is a mixture of the jaðar and the heath formations,
and belt 4, finally, is a mixture of the heath and the fell-field forma-
tions.
Actually it is quite natural that the formations are not so sharply
distinguished from each other here as in other places, especially if we
consider that they are interwoven in each other in small patches. This
is especially remarkable on the rústs. It should not be forgotten, either,
that the greater number of the flás are in a changing stage, in particular
the rústs. It is remarkable that the heath, melur, and sand formations
are intermixed on the tops of the rústs though these formations are
generally sharply delimited; however, this mixture is chiefly found
where the rústs are very unstable, that is to say, where they are drying
up and the crack systems in them are most strongly developed, while
at the same time the wind erosion is the most influential. Under these
circumstances the vegetation of the rústs assumes the character of the
melur or sand, the rústs then affording similar conditions to the plants
to those found in these formations. On the rústs on which no note-
worthy wind erosion takes place, a pure, closed heath vegetation is
found. In the flás investigated the shrub heath is the commonest forma-
tion, but the Grimmia heath also occurs. Above I have pointed out
the relationship of one of the associations of belt 3 to the snow-patch
formation.
Finally, I will briefly mention the development and distribution of
the flá in Iceland. Hannesson (1928, p. 141) summarises the
main features of his view as to the distribution and development of
the flá as follows (translated from the Danish):