Rit (Vísindafélag Íslendinga) - 01.06.1975, Page 115

lysis from the Scirpus mire. The H percentage is high as well.
The ground was relatively dry where the analysis was made and
only gently sloping.
64. S. cæspitosus — Equisetum palustre — Menyanthes
trifoliata sociation
The only available observations of this sociation are from Vatns-
nes in Húnavatnssýsla where it is widely distributed and the same
probably applies to other coastal points in the north. It may be
distinguished from the preceding Scirpus sociations by the fact that
E. angustifolium has mostly disappeared and that E. palustre and
M. trifoliata which have either been rare species in the other
sociations or completely absent, are dominant here, both in physi-
ognomy and covering. The composition of species in this sociation
is remarkable in one respect; i.e. species from the driest Equisetum
and the dampest Meynanthes divisions of the mire are joint domi-
nants. This shows that the ground-water level is not always a
decisive factor regarding the distribution of all mire species. Other
species which occur to a considerable extent are: Vaccinium uligi-
nosum, C. nigra and C. rariflora. The following are almost con-
stant: Polygonum vivipariun, Pinguicula vulgaris, Carex capillaris
and Selaginella selaginoides. The following are frequent: Thalic-
trum alpinum, Carex panicea, C. microglochin and Juncus alpinus.
This sociation generally includes the largest number of species of
all the sociations in the Scirpus mire. The biological spectrum does
not differ significantly, except that the HH percentage is fairly
high, but HH was mostly absent in the other sociations.
The sociation occurs mainly in relatively dry, sloping mires with
a flat surface and on the Vatnsnes peninsula it occurs almost ex-
clusively in the driest mire-patches or towards the outer borders
of wet mires and flói tracts. Analyses 13 and 14 show this very
distinctly. Analysis 15 differs from the others in some ways and
should perhaps be defined as a separate sociation. A Scirpus cæs-
pitosus — M. trifoliata — Carex chordorrhiza sociation. There the
ground is damper and slopes less than at the other locations, so
that it comes to resemble flói topography. Red clay is abundant
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