Rit (Vísindafélag Íslendinga) - 01.06.1975, Page 126

believes it to be eutroph-mesotrophic and Pesola and Brenner clas-
sify it as indifferent. Considering its main accompanying species
in Iceland it becomes anything but easy to classify it among acidi-
philous species. Among other species which occur extensively in
this sociation Equisetum pratense might be mentioned, since it is
a dominant species in one of the analyses. This indicates an even
closer affinity to the grassfield where it is a constant plant and
often dominant. I have some observations of this sociation from
Hlaðir in Hörgárdalur where it is widely distributed. Agrostis
tenuis is generally less noticeable there than in the observations
mentioned here. Equisetum palustre, on the other hand, is more
noticeable there and Carex nigra often has almost as large a
covering as D. cæspitosa.
The biological spectrum closely resembes that of 68, with a very
high E and H percentage, but Ch practically absent. This indicates
close affinity to dry-ground sociations and shows distinctly that
the drying out of the soil results in increased H percentage, whereas
the G percentage is proportionately reduced, other features of the
topography remaining unchanged.
As has been pointed out already this sociation grows in the driest
mire tracts where the ground water level is lowest and the soil
never flooded, except perhaps during spring thaws, and possibly
in the event of prolonged rainy spells. The slope is rather insignifi-
cant, but the mounds are fairly coarse, resulting in a difference in
vegetation between mounds and hollows, so that C. nigra grows
exclusively in the hollows and on the sides of the mounds. There
is no particular comment to be made on individual analyses.
74. Nardus strieta — Anthoxanthum odoratuin sociation
(Tab. XYx A-B 8-10)
Nardus stricta sometimes occurs — generally on a small scale —
in mire sociations, particularly where the snow cover tends to linger,
for it is by nature a snow-patch species and thrives best in grassy
depressions and on hillsides, especially mountain slopes. It is most
widely distributed in coastal districts where an oceanic climate
prevails and its distribution corresponds for the most part to that
126