Greinar (Vísindafélag Íslendinga) - 01.01.1967, Page 39

THE VASCULAR FLORA
OF THE OUTER WESTMAN ISLANDS
By
STURLA FRIDRIKSSON* AND BJÖRN JOHNSEN
Abstract
A study of the vascular flora of eleven outer members of the
Westman Islands off the southern coast of Iceland was performed
in the summers of 1965 and 1966.
These islands and skerries have been created by volcanic activity,
the most recent member, the island of Surtsey, being built up during
an eruption which started on November 14th 1963.
The bedrock of the islands is a formation of a palagonite tuff or
basaltic lava. The soil is loessy, often rich in organic matter due to
extensive bird droppings.
In comparison with the mainland the islands have a relatively
warm and moist climate. The vegetation which forms a mantle on
the high, often precipitious, rocks is more European than Arctic in
origin. It is prolific but scanty in species with a total of only 33 spe-
cies of vascular plants, ranging from 23 on the largest island to only
two or three on the smallest skerries.
In general the vegetation on the larger islands is predominated
by grasses, especially Festuca rubra, which seems to be favoured by
the selective environmental conditions present, such as periods of
drought, high winds, frequent splashing of sea water and high fer-
tility level of the soil.
The vegetation was classified into four plant communities, the
puffin colony vegetation, the dry meadow land, the coastal cliff vege-
tation and the angelica cluster. The dry meadow land is most ex-
tensive on the larger islands, the puffin colony vegetation is closer
to the shore and dominates on the smaller islands, whereas the coastal
cliff vegetation is mainly found on the outermost skerries and as a
fringe around the grass land on the larger islands. The angelica
cluster is only on shelves :n the cliffs.
Although the dispersal of plants to the islands is to some extent
restricted, the limited number of plant species is chiefly governed
by the highly special environment conditions present. And as the
* Agricultural Research Institute, Reykjavik, Iceland.