Greinar (Vísindafélag Íslendinga) - 01.01.1967, Blaðsíða 58

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present, though not occurring in the present measure-
ments of the area. This change in the flora can also be
explained by the fact that annual species are generally
subject to substantial fluctuations from one year to the
next.
There is a large puffin colony on Bjarnarey. The results
of point-measurements 3, 5 and 6 in Table IV show that
the dominant species of the puffin colony is Festuca rubra
with about 58% coverage, associated species being Stel-
laria media with 20% coverage, and Poa pratensis with
11% coverage. The Poa is found especially on the fringes
of the puffin colony, forming there a kind of marginal
strip, as on Ellidaey. Agrostis tenuis grows similarily to
some extent on the outskirts of the puffin colony, cover-
ing about 3%. Other species growing in the puffin colony,
covering about 6% in all, are: Rumex acetosa, Ranunculus
acris and Cerastium caespitosum. In the puffin colony it
seems that Cerastium and Poa trivialis have given way
to Ranunculus and Rumex since measured in 1933. Two
years before our present observation the grazing of sheep
on the island ceased, and this has undoubtedly had some
effect on the composition of vegetation. As there have
been no sheep present for the last two years to hold the
extensive growth of grass in check, the wilted grass accu-
mulates to a still greater extent than before without any
appreciable decomposition and forms a thick organic layer.
Underneath this mat the sward may be stifled. Patches of
decaying vegetation are thus to be seen in a number of
places.
To throw further light on the production of individual
plant communities on Bjarnarey the yield was sampled
by three cuttings. Samples taken from the puffin colony
gave a yield of 4,700 kg and 4,900 kg per hectare. A sample
taken from the dry meadow land gave substantially less,
e.g. 2,700 kg. The two former samples were fully com-
parable with the yield given by cultivated land under reg-
ular application of fertilizers.
At Hvannhilla on the northern side of the island the