Greinar (Vísindafélag Íslendinga) - 01.01.1967, Blaðsíða 48

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a break in the fescue cover, the associated species have
a chance to establish themselves.
Whenever the breeding grounds of puffin are densely
populated the growth of the red fescue is hampered by
the excavation of the birds. On these occasions the asso-
ciated species are favoured, sometimes even allowing the
Matricaria to predominate, but, in rare instances, Coch-
learia and Atriplex occupy the space.
Apparently this high fertility level, the special water
retention of the turf soil, as well as the intense aeration
caused by the digging, play an important role in this
selective habitat. The soils differ in the extent of aera-
tion from other highly fertile soils in Iceland, such as
those of hayfields in the neighbourhood of stables and
farmhouses. In that case Poa annua dominates, but this
species is hardly present in the vegetation of the puffin
colony, except in one instance, i.e. on the island of Súlna-
sker, where it was found growing on the edge of a small
basin containing rain water.
H. The dry meadow land vegetation has a wide distri-
bution, being the second largest plant association on the
southern islands and predominating on the northern is-
lands. It is situated on the level or sloping summits and
where the soil is dry and too shallow for the puffin to
dig their nesting holes (The puffin colony association can
be regarded as a derivative of meadow land as the puffin
hardly establishes nesting colonies except in grass cover-
ed soil. On some of the islands any pure meadow land is
hardly to be found as it is occupied and deformed by the
presence of the puffin). The soil of the dry meadow land
is rich in organic matter due to the high annual produc-
tivity of this community and its low decomposition. A
layer of turf is thus formed at the top. On the southern-
most island this top layer includes some fresh volcanic
ash derived from the Surtsey eruption. The thickness of
the ash varies in proportion to the distance from its
source of origin. On the island Álsey 14 km distant from
Surtsey the ash layer was 2—3 cm thick. Below the turf