Fróðskaparrit - 31.12.2000, Side 40

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A REVIEW OF PLANT COMMUNITIES OF THE FAROE ISLANDS
Islands. Ostenfeld (1905-1908) made a
comprehensive description of the vegeta-
tion into associations based on observa-
tions. Bocher (1937; 1940) and Hansen
(1972) used the method developed by the
Danish botanist, Raunkiær, to sample veg-
etation. They also registered frequencies of
species’ occurrence. Bocher (1937; 1940)
also used the Hult-Sernander five-degree
scale to measure the cover of vegetation.
Both of the scientists used the term socia-
tion to describe the plant communities,
based on dominant species. The term soci-
ation is used mostly in Scandinavia and fits
into the Braun-Blanquet system of associa-
tion. Dierssen (1982) and Tannhauser
(1995) used the Braun-Blanquet system to
define the associations.
Hobbs and Averis (1991) used the Na-
tional Vegetation Classification (Rodwell,
1991 -1995). In their system, a community
is roughly equivalent to a Braun-Blanquet
association.
In this paper the term association is used
and a summary is given in Appendix I.
Alpine Vegetation
Snow cover is very important in alpine ar-
eas, protecting the soil surface from frost
penetration in winter. Due to mild, sub-
zero winter temperatures, plants must be
able to withstand a snow-free winter, which
is liable to disturb the winter period of in-
activity. Only limited information on the
duration of the snow cover in the alpine ar-
eas is available from the Faroe Islands. Os-
tenfeld (1905-1908) made some observa-
tions in a two-year period and Bocher
(1937) had some information from local
people. Meteorological information on the
duration of snow cover in Tórshavn in the
period 1961-1991 shows that January had
the maximum number of days of snow cov-
er (10.8 days), while the period from May
to October had no snow cover (Cappelen
andLaursen, 1998).
The most distinctive features in the
alpine zone are the flat mountaintops form-
ing “fell fields”, described for the first time
in Greenland by Warming (1888). These
flat pastures are formed as a result of ero-
sion and one finds them from an elevation
of a few hundred metres up to the highest
mountaintop (882 m). Such plateau-like
areas are exposed to strong winds, and the
substrate freezes and thaws repeatedly.
Most of these areas consist of a mosaic of
cliff surfaces with moss and lichens, and a
few higher plants. The vegetation is very
distinctive, though sparse. It is the instabil-
ity of the ground and its constant movement
that causes the scarcity of flora.
The most common plants in the alpine
zone are Koenigia islanclica, Silene acciulis,
Luzula spicata, Alchemilla alpina, Bistorta
vivipara, Juncus trifidus, Deschampsia
alpina, Saxifraga rosacea, Loiseleuria
procumbens, Sibbaldia procumbens, and
Salix herbacea. Ranunculus glacialis, Pa-
paver radicatum, and Omalotheca supina
occur on the highest mountain peaks only.
In the fell fields, a Koenigia - Ranunculus
glacialis association has been described at
730 m a.s.l. This association is strongly in-
fluenced by species like Salix herbacea,
Racomitrium lanuginosum, and R. fascicu-
lare (Bocher, 1937). In two places, at alti-
tudes of 200 and 350 m.a.s.l., respectively,