Jökull - 01.01.2004, Blaðsíða 7

Theories on migration and history of the North-Atlantic flora: a review
dicated that only the hardiest plants could have sur-
vived. Later, Fredskild (1973) also supported this
view. Funder, who published the first pollen diagrams
from east Greenland in 1978, also studied the area’s
geomorphology and glacial geology. The latter stud-
ies led him to conclude that some lowland areas in
east Greenland were ice-free during the last glacia-
tion. Even though Funder’s pollen diagrams indicate
that many species were Holocene immigrants, he con-
cluded that some species could have survived the ice
age (Funder, 1979; Bennike, 1999). Sediments con-
taining a macroflora of bryophytes and few herbs have
recently been studied in NE Greenland. It has been
concluded that the woody plants found in these early
Holocene sediments did not all survive the last glacia-
tion in nonglaciated areas. However, it is speculated
that a few species of vascular plants may have sur-
vived (Bennike et al., 1999).
TABULA RASA AFTER ALL?
As mentioned earlier, participants at the symposium
in Iceland in 1962, on the North Atlantic biota and
their history, agreed that glacial survival had replaced
the tabula rasa theory (Löve and Löve, 1963). How-
ever, a different picture has gradually been emerging
over the last decades as knowledge about the Pleis-
tocene climate, the ocean floor and tectonic move-
ments has accumulated and become more difficult to
reconcile with the refugia theory (Buckland and Dug-
more, 1991). For example, putative land connec-
tions between North America and Europe have now
been pushed back at least 15 million years (Laughton,
1971; Nilsen, 1978; Buckland and Dugmore, 1991).
In 1987, Nordal reconsidered the tabula rasa hy-
pothesis in an article titled “Tabula Rasa After All?”
Nordal queried earlier interpretations of evolutionary
rates and went on to consider what she proposed was
the most parsimonious hypothesis for the putative en-
demism in the Scandinavian flora and a reinterpreta-
tion of the three main arguments for glacial survival:
1) The west-arctic element,
2) The alpine endemic element and
3) The disjunction and centricity of the alpine flora in
Scandinavia.
1) The West-Arctic Element
As Nordal (1987) emphasized, geologists do not agree
on the timing of the ultimate disappearance of the
Pleistocene North-Atlantic land bridge. Many believe
that this happened over two million years ago and
some even claimed that the main ridge platform sank
below sea level about 15 million years ago (Nordal,
1987). Recent evidence indicates that direct land con-
nection between southern Greenland and Europe was
broken in the early Eocene (approx. 50 M yrs ago), al-
lowing Atlantic waters to flow into the Arctic Ocean
(Marincovich et al., 1990; Tiffney, 2000; Tiffney and
Manchester, 2001).
Reconstruction of glacial limits in Greenland in-
dicates that virtually all of Greenland was covered
with inland ice during the penultimate glacial stage.
If plant species did immigrate to Greenland via land
bridges, then they would have had to survive repeated
glacial periods during the last million years and this
is hard to reconcile with the above information (Ben-
nike, 1999). But could the Greenlandic flora survive
the last glacial period? Then, ice covered much larger
areas than it does today. However, fairly extensive
land areas and mountain peaks probably remained
non-glaciated where plants could have survived the
last glacial age in Greenland (Funder 1989; Bennike
1999). Paleoclimatic reconstructions from the Green-
land ice cores indicate mean annual temperatures as
much as 25◦C lower than the present (e.g. Dahl-
Jensen et al., 1998; Ganapolski et al., 1998), making
survival of most plant species impossible (Philipp and
Siegismund, 2003).
Nordal (1987) also challenged Dahl’s assertion
that the lack of west-arctic species in Siberia and the
Alps proved that the west- arctic element did not sur-
vive the last glaciation in Europe outside Scandinavia.
Fossil remains of Pedicularis hirsuta near London
have been used as proof that some west arctic species
may, after all, have survived the glaciation south of
the ice but since become extinct in W-Europe. To-
day, other amphi-Atlantic species are on the verge of
losing their southern area (e.g. Minuartia stricta), and
others may already have lost it (Nordal, 1987).
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