The Botany of Iceland - 01.12.1945, Side 72

STEINDÖR STEINDÓRSSON
4H
may exert their influence; I assume, however, that the abundant pre-
cipitation in the south country is the chief reason of the wide distribu-
tion of the grassy slopes in these regions.
(Tab. IX. A-B).
The chief associations of the brekkur vegetation are:
i. The Elyna Bellardi—Carex rigida-Ass. (Tab. IX. A-B, 1-3).
This association is found on the driest slopes, often in places where
the vegetation has to fight hard against the wind erosion. Dominant
species are Elyna Bellardi, Carex rigida, Thalictrum alpium, and
Galium silvestre, in addition Poa pratensis and Festuca rubra are
present in considerable quantities. The ground vegetation is dense and
continuous. Analyses 1-2 were taken in the mountain Sáta on Land-
mannaafrjettur, in the east-facing slope, which is very steep but without
knolls of any kind. Hardly any moss is found. In several places the
vegetation is intersected by belts eroded by the wind. In certain places
patches occur which are entirely dominated by Poa pratensis and
Festuca rubra in company with Agrostis canina. Analysis 3 is from
Síðumannaafrjettur; although this locality is situated about 200 m
below the other two, there is no noteworthy difference in the vegetation.
The association is fairly rich in species. The A percentage is re-
latively high. Analysis 2 shows a higher A percentage than analysis 1 ;
this is possibly because it is situated c. 50 m above analysis 1 and was
taken near the boundary of the Grimmia heath. H is the dominant life-
form, and Ch is not noticeably represented. The association, which
must be regarded as the most typical of the associations of the brekkur
formation, is widely distributed on Landmannaafrjettur. It occurs here
and there on Síðumannaafrjettur, but otherwise I did not encounter
it except in Víðidalur, where it is only sparsely distributed.
2. Salix herbacea—Polygonum viviparum-Ass. (Tab. IX. A-B, 4-7).
In this association the ground vegetation is hardly continuous, the
Gramineae and Elyna have been reduced in number, while Salix herba-
cea and Polygonum vivipflrum have become dominants. It depends
somewhat on the locality, which species are the most conspicuous in
addition to these two; the most frequent are: Festuca rubra, Carex