Greinar (Vísindafélag Íslendinga) - 01.01.1967, Blaðsíða 46

44
Vegetation
The flora of the Westman Islands consists of 150 spe-
cies of vascular plants according to Johnsen (1939). All
the species recorded on the outer islands during the pre-
sent study are similarily found growing on Heimaey. On
these islands the vegetation is prolific but scanty in spe-
cies, with a total of only 33 species of vascular plants.
On Ellidaey, the largest of the outer islands, the number
of species is 23, but on the pinnacles of Geirfuglasker and
Thrídrangar the species recorded were four and two re-
spectively. The species found on each individual island
are listed in Table II.
A attempt was made to classify the species of the outer
Westman Islands according to geographical distribution
and life forms. The species are compared with those of
four other Icelandic isolates. Three of these are tuff
mountains isoiated by alluvial gravel and sand, and situ-
ated on the mainland in the neighbourhood of Mýrdalur,
Southern Iceland. The number of species found were as
follows: Pétursey 73, Hjörleifshöfdi 75, and Hafursey 89
species. The fourth isolate chosen for comparison is the
island of Grímsey, situated off the north coast of Iceland
with a total of 116 species (Table III).
The comparison shows that the number of Arctic spe-
cies increases with increased latitude, changing from no
Arctic element in the flora of Súlnasker and Geirfugla-
sker to 42% Arctic species in the flora of Grímsey. The
majority of the species of the outer Westman Islands, or
74% to 100%, are of European type. This difference of
geographical forms probably reflects the thermal condi-
tion of these respective locations rather than a difference
in floral communities of some hypothetical glacial refugia
in the northern and southern part of the country (see
Mölholm-Hansen 1930 for classification).
The ratio of various life forms (Raunkiaer 1907) on the
islets is comparable to that of Heimaey, but differs from
the three inland isolates as well as from Grímsey. Chameo-