Náttúrufræðingurinn - 1963, Side 49

NÁTT Ú R U F RÆÐIN G U RIN N
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species in the indigenous flora is believed to liave survived at least the last
glacial period. This elenient is assumed to liave dispersed to the island over a
land connection during the last interglacial period. In the present article the
author opposes the view o£ glacial survival of sucli a large element, and
points out the facts that other islands in the north such as Jan Mayen have
an arctic flora in spite of being totally covered with ice during the last glacia-
tion. Furthermore tlie author expresses the view that the major part, if not
all of the present llora, might have dispersed over the ocean in post-glacial
time.
No true endemic plant species are met with in Iceland, and the centric distri-
bution of some species is not necessarily an indication of tlieir glacial survival.
The plants may liave a centric distribution because of a late immigration or
due to certain environmental condition at the centric locations, favouring cer-
tain elements of the flora. Thus in the central-north mountain ridge the alpine
plants are dominating. In the central-south region the temporate element is
met witli. In the eastern region there are some species which may have rather
recently dispersed from Scandinavia and on the western peninsula there are
centers including sorne species of circumpolar and bis-Atlantic distribution.
Some botanists hold the view that the selection during the glaciation was
so strong that only a few ecotypes survived on mountain tops and had lost
the ability to spred. The sanie effect might be obtained through a sporadic
immigration of single plants by later dispersal.
The means of transport to the island is by way of ocean currents, drift wood
and drifting ice; winds; birds and man. These elements are discussed briefly.
It is pointed out that spores of Pteridophytes and seed of willows and poplars
can drift by wind. Seed of Angelica and possibly number ol' other plants
float for a long time on water, and drifting ice can carry parts of vegetation
without injury by salt water. As birds do transport seed to isolated inland
places they have likely played a great part in transporting seed froni the North-
European continent. Seed carried by tlie craw of tlie ptarmigan is postulatcd
as a way of transport. Man has imported one species every 3 years since the
turn of the cemury. It is therefore likely that he has liad a major influence
on the total number of species of the flora during the 1000 years of his dwel-
ling in Iceland.
Icefree areas may liave carried sonie connnon plants of the artic vegetation
during the last ice age. Most of these, however, have a wide distribution at
present and thus do not point to a definate center as a possible site of glacial
survival.