Jökull - 01.01.2004, Blaðsíða 5

Theories on migration and history of the North-Atlantic flora: a review
DID THE ICELANDIC FLORA SURVIVE
THE ICE AGE?
Lindroth’s and Gelting’s suggestion that plants sur-
vived in Iceland in ice-free refugia, as mentioned
earlier, inspired the Icelandic botanist Steindór
Steindórsson to make further studies to test this the-
ory. Already in 1949, Steindórsson pointed out five
areas (which he called districts) in Iceland, which
he considered possible refugia. Later the districts
became six (Steindórsson, 1963). Their definition
was based on the distribution of about 100 vascu-
lar plant species that seemed to be concentrated in
them. Some had highly discontinuous distributions in
Iceland with no obvious natural obstacles to explain
the gaps (Steindórsson, 1963). Steindórsson com-
pared these six districts with the areas that Thórarins-
son (1937) had earlier suggested had been ice-free
during the glacial ages and they appeared to match
well. These plant centres pointed out by Steindórsson
(1963) were: (1) The Breiðafjörður district, (2) Vest-
firðir district, (3) Eyjafjörður district, (4) Austfirðir
district, (5) Mýrdalur district and (6) Hvalfjörður dis-
trict.
According to Steindórsson (1963) at least 13
plant species, classified as west-arctic in Scandi-
navia, are also found in Iceland: Campanula uni-
flora, Carex macloviana, C. nardina, C. rufina,
Cerastium articum, Draba norvegica, Epilobium lact-
ifolium, Erigeron humilis, Euphrasia frigida, Festuca
vivipara, Pedicularis flammea, Sagina caespitosa and
Stellaria calycantha. Five (C. uniflora, C. maclo-
viana, C. nardina, E. humilis and S. caespitosa) have
a distinct centre in the Eyjafjördur district (Steindórs-
son, 1963). Eight are found at more than 300 m a.s.l.
in Iceland and some even up to 1000 m.
Steindórsson (1963) not only proposed the west-
arctic species as ice-age candidates, he also consid-
ered the so-called North Atlantic species, a group
closely affiliated with the west-arctic group, to be
ice age survivors. The five plant species, which
Steindórsson sorted under this group, were Alchemilla
faeroensis, Arenaria norvegica, Poa flexuosa, Sax-
ifraga aizoon and Carex bicolor. Of these 18 (west-
arctic and North Atlantic) species, 11 have a distinct
centric distribution in Iceland. Two more species
showed the same kind of tendencies but the rest dis-
played no centricity at all (Steindórsson, 1963). Other
centric species in Iceland were e.g. classified as alpine
(>200 m) or lowland (<200 m) plants. The alpine
group contains 18 species and the lowland group 37
species (Steindórsson, 1963).
Altogether, Steindórsson (1963) pointed out that
the six districts contained 100 species almost exclu-
sively limited to them or to other places with possible
nunatak landscape. However, some of these districts
are now considered very unlikely to have been ice-free
areas, notably the Mýrdalur district (Einarsson,1963)
(Figure 1).
Steindórsson (1963) himself pointed out that
“the Mýrdalur district may be considered a dubious
refugium area”. Mýrdalur enjoys the mildest climate
in Iceland and most of its exclusive species e.g. Plan-
tago lanceolata, Succisa pratensis and Vicia sepium,
are thermophilic with their present distribution in Ice-
land most likely limited by temperature, as Steindórs-
son (1964) himself recognized.
Steindórsson (1963) asked if the plant species
mentioned above immigrated in postglacial time,
should they not just as easily have taken root in other
parts of Iceland? Glacial survival was therefore the
most probable explanation for their distribution.
In 1964, Steindórsson suggested that not only had
the 100 species already mentioned survived, but that
up to 214 species, 48% of the present vascular flora,
may have survived the Pleistocene in Iceland. He di-
vided the Icelandic flora into three groups:
1) 214 species (48%) that survived in ice-free refugia,
2) 92 species brought in by humans (21%) and
3) 136 of uncertain origin (31%).
Steindórsson was clearly a great supporter of the the-
ory of glacial survival in Iceland.
As mentioned before, Friðriksson (1962) sup-
ported the tabula rasa theory. By 1978, his views had
changed and he had become an adherent to the the-
ory of survival. At that time, Friðriksson was much
involved in monitoring the immigration of plants and
animals to the new island of Surtsey (Buckland and
Dugmore, 1991).
Hallgrímsson (1969, 1970) divided Iceland into
five climatic areas and grouped plant species accord-
JÖKULL No. 54 5