Fróðskaparrit - 01.01.1998, Síða 12

18
A BIOGEOGRAPHIC ANALYSIS OF THE PLANTS IN THE FAROEISLANDS
The number of animal and plant species
on remote islands has been the subject of
many studies, see e.g. Williamson (1981).
That is theoretically interesting, among
other things, because many areas, and on
the continents as well, may be considered
islands in an ocean. Lakes behave like is-
lands in an ocean of land, mountain peeks
are to alpine animals and plants like islands
in an ocean of lowlands, and forests are like
islands in a sea of cultured landscape. Ever
since the late 1960s, such island biogeo-
graphical speculations have been nume-
rous, and they may also have a practical
function, e.g. when assessments must be
made as to how many species will become
extinct when the tropical rain forest disap-
pears (see e.g. Wilson 1992).
The present article deals with the number
of plant species on the Faroe Islands. For
several reasons, these islands are very suit-
ed to an investigation of the above correla-
tion: The total area of the Faroe Islands is
limited (118 by 75 km2), and there are large
distances to the nearest mainland (Norway:
675 km) and to other groups of islands (the
Shetlands: 300 km and Iceland: 450 km).
By comparison, the distances between the
single Faroe Islands are small. Finally, the
flora of the Islands is extensively described
in many studies.
Other biogeographical studies of the
Faroe Islands are Bengtson and Bloch
(1983) on birds and area, Bengtson (1982)
and Enckell et al. (1987) on invertebrates.
In the present article, we shall list the
number of Faroese vascular plants listed for
each individual island, according to infor-
mation in Hansen (1966). The result will be
used in a common mathematical model
concerning number of species and area. Be-
sides, we shall discuss the model, its weak-
nesses and the underlying causes for the
correlation.
Subsequently, we shall introduce an al-
ternative model to describe the correlation
between area and number of plant species.
In some aspects, this model is more acces-
sible than the currently used model.
Finally, our model will enable us to draw
up an index which permits us to make com-
parisons between the florae of the individ-
ual islands.
The material
Information on the number of species all
comes from Hansen (1966), who lists the
distribution of the vascular plants on the
Faroe Islands. The material basically origi-
nates from a field survey conducted in
1960-61.
In our study, we have included the plants
whose distribution has been listed on dot
maps in Hansen (1966), apart from a few
exceptions. Consequently, our material is
composed of such species which occur nat-
urally, which have been imported or natu-
ralised as well as species which have been
established ‘on a number of locations’ in
the Faroe Islands. We have excluded im-
ported species which have not become es-
tablished (no distribution map) and species
which have not been found during Hansens
(1966) research activities. Besides, we have
treated minor subspecies of hawkweed (Hi-
eracium sp.) as one species and the same
applies for subspecies of dandelion (Tarax-
acum sp.). A total of 294 species have been