Fróðskaparrit - 01.01.2004, Side 220

218 ALTITUDINAL DISTRIBUTION OF PLANT COMMUNITIES IN THE FAROE ISLANDS
phus loreus community. I concluđe from this study
that the three vegetation zones are found at consider-
ably lower altitudes than older studies demonstrated.
Introduction
ln recent years, interest in studying the ef-
fects of global climate change on vegeta-
lion has increased (e.g. Woodward, 1987;
Sykes etcil., 1996;Korner, 1998; Crawford,
2000) . According to the IPCC (Intergov-
ernmental Panel on Climate Change), the
average global temperature will increase
around 2-4°C in the 21st century (IPCC,
2001) . A potential weakening of the North
Atlantic Current, however, makes it uncer-
tain whether the climate in the Faroe Islands
will become warmer or colder (Hansen et
al., 2001).
The location of the Faroe Islands, direct-
ly in the path of the North Atlantic Current,
makes it unique for studying the effects of
global climate change, because these is-
lands are the only land areas that are com-
pletely surrounded by the North Atlantic
Current (Hansen et al. 2001; Christiansen
and Mortensen, 2002).
Lower elevations in the islands belong to
the temperate climate zone while the upper
elevations belong to the arctic climate zone
(Humlum and Christiansen, 1998; Chris-
tiansen and Mortensen, 2002). Therefore,
it is possible to study the dynamics of tem-
perate and arctic-alpine vegetation in the is-
lands. These previous studies based on tem-
perature and periglacial activity propose a
low arctic zone from 200 m a.s.l. and an
arctic zone from around 400 m a.s.l. (Hum-
lum and Christiansen, 1998; Christiansen
and Mortensen, 2002).
The predominant vegetation in the Faroe
Islands is grassland; it occurs from sea lev-
el to mountaintop. Three vegetation zones
have been previously defíned in the Faroe
Islands. The lowland vegetation zone (0-
300 m a.s.l) has Calluna vulgaris heaths
and Nardus stricta vegetation with Hylo-
comium splendens in the moss layer. At
higher altitudes (300-500 m a.s.l.), Nardus
stricta is still dominant, but the heath veg-
etation almost disappears. In the moss lay-
er, both Hylocomium splendens and Raco-
mitrium spp. dominate, with Racomitrium
lanuginosum as the most frequent species.
At the highest altitudes (500-882 m a.s.l.),
Racomitrium spp. heaths are the character-
istic vegetation, Salix herbacea is contmon
and Calluna heaths are absent (Bocher,
1937)
The alpine zone has usually been defined
as a zone that is delimited downwards by
the mean isotherm of 10°C for the warm-
est month, also consistent with the tree line
(Billings and Mooney, 1968; Troll, 1973;
Korner, 1998; 1999; Mark et al., 2001).
This zone usually has a wide altitude range
and a large diversity of plant communities
composed of various dominant life-forms.
On the basis of these differences, the alpine
zone is usually subdivided into a lower al-
pine zone and an alpine zone (Ahti et al.,
1968).
This paper presents the first quantitative
study of the vegetation in the Faroe Islands
with systematic sampling along continuous
altitudinal transects, from 100 m a.s.l. up to
856 m a.s.l. Five mountains in the northern
part of the Faroe Islands are included (Fig.
1). The aim of this study is to describe the