The Botany of Iceland - 01.12.1945, Page 34

III. THE PLANT COMMUNITIES
i. SYNOPSIS
Having treated above the topography and the climate, I shall now
describe the individual plant communities. If we look at the conditions
under which the plants live in the Icelandic highland, we shall soon
be convinced that it is the moisture of the soil, possibly in connection
with the snow-covering, which exerts the greatest influence on the
occurrence of the species and their formation of communities. I have
therefore chosen to enumerate here the different formations according
to their relations to the moisture of the soil. I assume that in this way
we shall come nearest to the natural succession as regards their develop-
ment. But naturally other factors than the moisture play a part in the
development of the formations, so that according to this succession we
cannot expect to find them accurately grouped as far as their inter-
relationship is concerned. I shall not here deal with the problem of
the formation of the plant communities, as my purpose has been to
define and describe the formations and their most important associa-
tions and to give a summary of the conditions under which they thrive
and of their distribution in the areas investigated.
I have chosen the method of defining and describing the smallest
plant communities according to their composition of species. These
smallest communities, the associations, I define in accordance with
Th. Fries (1913, p- 47): “Eine Assoziation ist ein Vegetations-
typus von im grossen und ganzen einheitlicher physiognomischer Zu-
sammensetzung”. B r a u n-B 1 a n q u e t (1928, p. 20) says that
“Vegetationsflecke mit áhnlicher Artenzusammensetzung werden zu
einem abstrakten Typus zusammengefuhrt. Dieser Typus ist die “Asso-
ziation”, die einzelnen Flecke sind die “Assoziationsindividuen” oder
Einzelbestande”. I am afraid, however, that within the associations
described by me there is in places such great disagreement between the
“Einzelbestande” that they should more correctly be termed variants