Jökull - 01.01.2004, Blaðsíða 2

Hafdís Hanna Ægisdóttir and Þóra Ellen Þórhallsdóttir
sequently became the foundation of the theory of tab-
ula rasa i.e. that as a result the entire Scandinavian
biota had been erased and must have immigrated af-
ter the “ice age” from parts of central Europe, British
Isles, and Siberia where plants and animals had been
able to survive (Dahl, 1955).
The tabula rasa theory was already supported
with strong arguments. When the biota of Scandi-
navia was compared with biota from unglaciated ar-
eas, the former had remarkably few endemics. The
tabula rasa theory could explain this by the youth
of the flora and fauna. The time span from the “ice
age” was not sufficient for the development of new
species (Dahl, 1955). Nathorst (1892) and Ander-
son (1906) were the first to report fossils of arctic
and alpine plants in southern Scandinavia (e.g. Betula
nana, Dryas octopetala, Diapensia lapponica, Sax-
ifraga oppositifolia and Thalictrum alpinum). These
fossils were found in deposits formed under glacial
conditions after the retreat of the inland ice of the
last glacial age (Dahl, 1955). By this time, the tab-
ula rasa theory was firmly established. Migrations
along the borders of the waning ice could explain the
presence of alpine and arctic plant species in Scandi-
navia (Dahl, 1955). In Iceland the main supporters of
the tabula rasa theory were the geologist Thorvaldur
Thoroddsen (1911; 1914) and the botanist Stefán Stef-
ánsson (1913). Later Sturla Friðriksson (1962) also
supported the theory.
The Glacial Survival Theory
In Scandinavia, Blytt (1882) was the first to oppose
the tabula rasa theory and come up with the idea of
glacial survival e.g. plants surviving the last or sev-
eral of the Pleistocene glaciations in ice-free refugia.
Blytt concluded that most of the Norwegian mountain
flora consisted of plant species with their main centre
of distribution in Greenland and North America. To
explain the occurrence of the Greenlandic/American
element in the mountain flora of Norway, which he
called the west-arctic element, he proposed that a land
bridge had connected Greenland to western Norway
via Iceland and the Faeroes during the Quaternary.
This land bridge would have been glaciated only in
part and never simultaneously throughout, thus facil-
itating dispersal of plants in both directions (Blytt,
1893; Nordhagen, 1963).
The Swedish botanist Rutger Sernander further
formulated the glacial survival theory in 1896. He
pointed out that in some of the Norwegian (Dovre,
Nordland and Finnmark) and Swedish (Jamtland
and Harjedalen) mountains, remnants from the inter-
glacial flora of Scandinavia, which had not been over-
run by the second inland ice, had been preserved. Ser-
nander’s theory received almost unanimous support
from biogeographers dealing with the distribution and
history of plant species in the North Atlantic regions
at that time e.g. Hansen (1904), Fries (1913) and oth-
ers (Dahl, 1955).
The idea of glacial survival also became popu-
lar in Iceland. The possibility of plants surviving
glacial periods in Iceland was first mentioned in the
works of Lindroth (1931) and Gelting (1934). As
early as 1879, Kornerup had proposed the existence
of un-glaciated areas in western Greenland during the
last glacial period. Warming (1888) and many oth-
ers agreed with Kornerup, and other ice-free areas in
Greenland were suggested (see e.g. Gelting, 1934).
It was even proposed that the most northerly part of
Greenland (northernmost Peary Land) had never been
glaciated (Koch, 1928).
The macro-lichen flora of south Greenland has a
strong resemblance to the Scandinavian arctic/alpine
macro-lichen flora (Dahl, 1946). Dahl maintained
that post-glacial migration could not explain this affin-
ity, thus the flora must have survived the last glacial
period in south Greenland or in areas nearby.
In Svalbard, various areas have been proposed as
ice-free Pleistocene islands and candidates for refu-
gia for different plant groups (Dahl, 1946). Lichen
studies in Spitsbergen convinced Lynge (1938) that
the northernmost part of Spitsbergen had remained
unglaciated. King Karl’s Land (in eastern Sval-
bard) (Nathorst, 1901; 1910) and Björnoya (Hadac̆,
1941) were also considered to have escaped glaciation
(Dahl, 1946).
The Geologists’ Point of View
Iceland
Were ice-free refugia geologically possible in Ice-
land during the ice age? At the beginning of the
2 JÖKULL No. 54