Greinar (Vísindafélag Íslendinga) - 01.01.1967, Blaðsíða 68

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The difference in distribution of these species is hard-
ly due to difference in temperature, humidity and light,
as it seems to be more or less the same in both types
of associations. More likely it is due to a difference in fer-
tility level of the soil. No qualitative analysis of the soil
was performed, but from simple observation it is clear
that the quantity of droppings in the two principal asso-
ciations differs considerably. In the puffin colony itself,
which the birds constantly frequent, the amount of drop-
pings must be many times greater than that in the dry
meadow land. In fact where the puffin nests are densest
the growth has been destroyed by droppings. Judging by
this, the Festuca and its associated species are the most
manure tolerant. After these comes the Poa, which flou-
rishes in the marginal zones, but the Agrostis is domi-
nant in the dry meadow land where droppings are scan-
tiest. This is especially evident on the largest of the is-
lands, Ellidaey, where the dry meadow land is the most
extensive. As the islands decrease in area, the amount
of dry meadow land gets less and the proportion of
puffin colony vegetation to the whole increases, until it
becomes the predominant association. On islands of me-
dium size such as Álsey and Sudurey true dry meadow
land disappears and a marginal strip takes its place. Three
factors are paramount in determining the extent of the
puffin colony. First, there must be sufficient depth of soil
for the birds to dig their burrows; second, there must be
a view of the sea; third, there must be an adequate slope,
for the puffin must be able to jump downwards in order
to take flight. From this it will be seen that the puffin
colony vegetation is to be found specially on the seaward
slopes, while the dry meadow land occurs in the middle
of the island where there is level ground, or in hollows
and places where the soil is shallow.
As the islands become yet smaller, the extent of the
puffin colony is reduced and coastal cliff vegetation takes
over. This is owing to the increased effect of wind and
sea, which makes the formation of top-soil more difficult.