Rit (Vísindafélag Íslendinga) - 01.06.1975, Blaðsíða 149

and mýri, or mýri and lieath. This is sometimes replaced by a
Juncus balticus jaðar.
The jaðar generally has a large nrnnber of species, although
there are exceptions, but the proportions of groups of species and
lifeforms depend on the topography in each particular instance.
a. Juncus balticus jaðar — Juncétum baltici
The most common plant community of the jaðar is the J. balticus
association and it may truly be regarded as the typical jaðar vege-
tation. J. balticus either grows in the jaðar proper, between mire
and dry ground, or in large or small patches within the mire tract.
In appearance this vegetation type clearly contrasts with its sur-
roundings because of the characteristic colouring and form of J.
balticus. In early summer it is dark green, but tums brownish to-
wards the autumn. In winter when the snow cover is light the
Juncus stalks often rise out of the snowy expanse, stiff and grey-
tsh in hue. In spring the white withered stalks are oddly at vari-
ance with the surrounding lush vegetation.
Outside the jaðar proper J. balticus often thrives on sandy, moist
fiver banks where it forms large expanses. Where glacial moraines
have been clad with vegetation there often occur extensive tracts
where J. balticus is a dominant species. There the ground is semi-
öioist, but drier than the mire. The distinguishing line between
the J. balticus areas and the mire often becomes rather vague how-
ever, since Carex nigra, the principal species of the mire, is the
constant accompanying species of J. balticus. I have seen this type
°f vegetation in its most extensive form in Skaftafellssýslur: Álfta-
ver, Meðalland and Mýrar. By far the most common accompany-
lng species of J. balticus is Festuca rubra, but Equisetum palustre
and C. nigra are somewhat less common. "Wherever depressions
have formed and the ground becomes damper J. balticus disap-
pears to be replaced by C. nigra or C. Lyngbyei, even in areas
which are only so slightly moist that the depressions dry out in
the summer. In Meðalland Hierochloe odorata was very common
ln the Juncus association. This vegetation type does not signifi-
cantly differ from the mire jaðar proper, but here the surface is
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