Rit (Vísindafélag Íslendinga) - 01.06.1975, Blaðsíða 56

Although Carex nigra occurs in various flói sociations sometimes
as dominant, it is never predominant in physiognomy and in most
areas it is hardly noticeable in covering, despite its high frequency.
Its hahitat is the mýri not the flói, and in the mýri it is as pre-
dominant as E. angustifolium is in the flói. This sociation is alto-
gether unique and has only been observed on one location, Fagri-
dalur in Brúaröræfi (approx. 600 metres ahove sea level). Never-
theless it often occurs in small patches in the lowland, hut most
often under specific circumstances.
Where the analysis is made there are very well developed ridges.
ahove which water collects, which disappears ahnost altogether in
the summer time, but the terrain remains very wet. "Where the
ridges are less elevated and a constant water dam does not develop
a normal Eriophorum flói occurs. The sociation grows in these flói
patches, which are subject to most prolonged flooding, and they
may be clearly distinguished from the Eriophorum flói, which sur-
rounds them. These patches resemble irrigation locks on meadow
tracts, where dams are huilt in the spring, but the terrain is allowed
to dry out during the summer. If Eriophorum flói is thus taken for
irrigation purposes, and dams and drainage ditches are well con-
structed, so that the water is at an adequate level in the irrigation
season, allowing the land subsequently to dry out, it inexorahly
changes into a C. nigra sociation, occasionally containing some
Calamagrostis. If on the other C. Lynghyei has been present in the
Eriophorum flói it soon hecomes predominant upon irrigation. This
I have clearly demonstrated in my work on the Flói Irrigation Pro-
ject. (Std. 1943, pp. 67-85). In the area in question the mound
ridges resemble dams, but for some reason the terrain gets to dry
out somewhat during the srunmer, so that C. nigra is able to grow
there and rot patches do not form in the soil. If the water does not
reach any significant flow, ponds develop above the ridges, traces of
which are often found near the observation site.
d. Carex rostrata flói — Caricétum rostratae
The third main division of the Icelandic flói areas is the Carex
rostrata flói. It is hardly as widely distributed as the Eriophorum
56