Greinar (Vísindafélag Íslendinga) - 01.01.1967, Blaðsíða 72

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land being composed of only a few species might indi-
cate that it has not reached the same advancement in
succession as that of Bjarnarey. The more complex dry
meadow land association on Bjarnarey may thus be a
more advanced succession or it may be a result of special
microclimatic factors such as the effect of shelter; condi-
tions of growth not existing elsewhere among the outer
islands.
It is evident that all these highly special environmental
factors cause great limitations to the number of plant
species and their association on the islands.
Although the migration of plants is restricted to some
extent by the isolation of the islands, the flora of each
individual island has to be regarded as being primarily
governed by the present environmental conditions.
Most of the old volcanic islands are of a comparatively
stable topography with a vegetation that has become sta-
bilized in four major types of climax communities in their
respective habitats. These have to some extent formed
a zonation extending from the splash zone at the lower
level with transition through the fertile soil of the puffin
colony to the dry, less fertile meadow lands of the upper
parts of the islands.
In contrast with these stable communities, the newly
formed island of Surtsey, which was completely bare, has
at present only a few pioneer plants. These have recently
colonized its developing beach and represent the first
stage of the primary succession. Through a study of the
colonization of the biota of Surtsey a great deal may be
learned about the ecology and the process of succession
on the islads.