Jökull - 01.12.1990, Blaðsíða 74

values (7-36 %) are steadily increasing within the first
two subzones, decreasing to a distinct minimum in
subzone KHM 2c. Both Gramineae and Cyperaceae
pollen are well represented throughout the zone. Three
subzones are recognized, KHM 2a, KHM 2b and KHM
2c.
KHM 2a (513,5-547,5 cm). Pollen samples num-
ber 5-11. The subzone is characterized by steadily
increasing Juniperus pollen values from 7 to 26 %.
Betula pollen values act in the same way. Salix and
Cyperaceae pollen values are decreasing. Gramineae
pollen are well represented attaining values of 28 %.
The herb pollen of Potentilla, Galium and Cruciferae
have a sparse but continuous representation. Other
herb pollen have both sparse and discontinuous repre-
sentation. Lycopodium annotinum spore frequencies
vary between 4 and 11%.
In this subzone Eu-Potamogeton pollen type has
a maximum attaining values of 40 %. Otherwise the
aquatics have the same composition as in KHM-1.
The subzone is named the Juniperus - Betula -
Salix - Cyperaceae Local Pollen Assemblage Subzone.
KHM 2b (489,5-513,5 cm). Pollen samples num-
ber 12-16. This subzone is characterized by the first
Betula maximum of 36 %. The pollen values of Ju-
niperus are between 4 and 9 %, which is a minimum
for the zone. The pollen frequency of Thalictrum
alpinum rises at the beginning of the subzone to 4 %
and is rather constant between 2 and 4 % within the
subzone. Both Polypodiaceae undiff. and Dryopteris
linneana (Gymnocarpium dryopteris) have a constant
representation of 2-5 % throughout the subzone.
In the zone spores of Isoetes echinospora appear
again, but are very sparse like all the other aquatic
pollen types.
The subzone is named the Betula - Gramineae -
Thalictrum alpinum - Polypodiaceae undiff. Local
Pollen Assemblage Subzone.
KHM 2c (469,5^189,5 cm). Pollen samples num-
ber 17-20. This subzone is characterized by the
second Juniperus maximum at the beginning of the
subzone, but Juniperus pollen values are decreasing
throughout the zone. Salix pollen values are still de-
creasing from about 6 % to below 1 %. Betula has a
minimum value of 10 % in the middle of the subzone.
Cyperaceae gain a maximum value of 47 %. Galium,
Thalictrum alpinum, Rumex type and Potentilla are
the herb pollen showing sparse but a continuous rep-
resentation. The same is the case for Polypodiaceae
undiff. spore frequencies, while Dryopteris linneana
has somewhat greater values of about 4 %.
Isoetes echinospora shows a distinct maximum
within the zone as does Eu-Potamogeton type.
The subzone is named the Juniperus - Cyperaceae
- Rumex type Local Pollen Assemblage Subzone.
KHM 3 (457M69,5 cm). Pollen samples number
21-23. This zone is characterized by increasing Be-
tula pollen values, exceeding 50 % at the upper limit
of the zone. Juniperus pollen values are decreasing,
as are Cyperaceae. Among the herbs Cyperaceae and
Gramineae are most abundant but Rumex type, Po-
tentilla, Ranunculus, Thalictrum alpinum and Com-
positae Liguliflorae are constantly but sparsely rep-
resented. All the Pteridiophytes except Lycopodium
selago are represented as in the preceding zones.
Of the aquatics Myriophyllum alterniflorum, Eu-
Potamogeton type, Hippuris vulgaris and Isoetes echi-
nospora are all represented.
The zone is named the Betula Local Pollen As-
semblage Zone.
SIZE MEASUREMENTS OF SUBFOSSIL
BETULA POLLEN
According to Stefánsson’s Flora (1948) Betula is
represented in Iceland by three indigenous species
and one hybrid: Betula pubescens Ehrh., B. coriacea
Gunnarss., B. nana L. and the hybrid B. nana L. x
pubescens Ehrh. Löve (1945) mentions B. callosa
Notö too, but assumes that B. tortuosa Led. (syn.
B. pubescens) is the most abundant tree or shrub.
Bjamason (1945) suggested some of the Betula in
Northwest Iceland to be of the westem type B. glan-
dulosa, having immigrated from Greenland. A recon-
naissance on the Icelandic birch woodland led to some
finds of species having the character of B. verrucosa.
This is assumed to be a later immigrant to the Icelandic
flora (Sigurðsson, 1977).
The problem of separating pollen of tree birch
(B. pubescens type) from the ecologically different
72 JÖKULL,No. 40, 1990