Jökull - 01.12.1986, Blaðsíða 52

occasional variations in the fossil biota imply varying
degrees of local wetness on the surface, there is insuffi-
cient evidence to regard this as anything other than
the result of the natural processes of bog growth (cf.
Moore & Bellamy, 1973), rather than as indications of
climatic change.
The limited evidence from the fossil seeds and
megaspores is shown in table 1. Only 5 taxa, distri-
buted among 4 samples are recorded, the matrix of
each being dominated by poorly preserved Sphagnum.
Most of the plants can be found on the bog at the pre-
sent day but clubmoss, Selaginella selaginoides, re-
presented by large numbers of megaspores in several
samples, is now confined to the upper slopes of Geita-
fjall, presumably having been shaded out by the
denser growth of grasses and sedges on the now drier
bog surface. The bog bean, Menyanthes trifoliata,
appears in KEl/4, a sample which is considerably
earlier than Landnám, the drier nature of the surface
is probably the reason for its absence from the bog at
the present day.
In virtually all samples, the beetle fauna (table 2) is,
not surprisingly, indicative of a bog environment.
Small pools of open water are indicated by the
Dytiscid water beetles Hydroporus nigrita and Agabus
bipustulatus. Hydraena britteni, on evidence from
elsewhere in Europe (Lohse, 1971; Balfour-Browne,
1958), probably lives in amongst the wet Sphagnum
cushions at the sides of the pools. Several of the
Staphylinids would also appear in the wet habitats on
the bog surface, including species of Stenus and Lath-
robium brunnipes. Somewhat drier areas are implied
by some of the Carabids but all might be found in an
intermittently rather less damp tussock and pool en-
vironment, where beetles such as Pterostichus dili-
gens, P. nigrita and Quedius umbrinus could occur
among the grasses and sedges and in the accumulation
of decaying plant debris. The paucity of phytophages
in the Icelandic fauna means that little can be added
to the list of plant species by way of the insects which
feed upon them. Both of the weevils Otiorhynchus
nodosus and Tropiphorus obtusus are polyphagous on
a wide variety of plants, the larvae feeding on the
roots (Lindroth et al., 1973).
Post-Landnám
Above the Landnám tephra, the impact of man
rapidly becomes apparent in the succession. The most
diverse flora occurs in sample BRl/2, from immedi-
ately below the —1357 tephra fall, a reflection of the
increased habitat variety created by human activities.
The flora includes the chickweed Stellaria media, a
plant if not introduced by man (Steindórsson, 1962)
much encouraged by his disturbance of the ground,
and the buttercup Ranunculus cf. acris may also
belong to the group of anthropochorous plants. The
limited nature of the flora, however, allows few con-
clusions and the beetle fauna can add little in terms of
information on the species of plant rather than the
general nature of the vegetation. Byrrhus fasciatus is a
moss feeder usually found in drier localities among
stones and mosses rather than in bogs but it is a
capable flier (Lindroth et al., 1973). The larvae of the
click beetle Hypnoidus riparius are generalised feeders
upon the roots of grassland vegetation and it is sugges-
tive of a somewhat drier situation. Since the imago is
flightless (op. cit.), it is probable that the area became
at least intermittently less boggy after Settlement. In
part, this may reflect the increased sediment input to
the basin (fig. 6) but peat cutting for fuel (fig. 4) must
also have altered the drainage pattern.
The weevils are more informative. Whilst Stropho-
somus melanogrammus has been taken in Iceland in
localities away from scrub (Larsson & Gígja, 1959;
Lindroth et al., 1973), it is more characteristic of birch
woodland, where the imago eats the leaves and young
shoots; it may be regarded as an Urwaldrelikt in the
Icelandic fauna, now surviving in such conserved
areas of woodland as those in Thórsmörk. Crucifers
are absent from the fossil record at Ketilsstadir, a con-
trast with the modern flora, where the shepherd’s
purse, Capsella bursapastoris, is frequent on the dis-
turbed ground around the farm and along the sides of
the road to Vík, and rock cress, Cardaminopsis
petraea, grows abundantly on the bare slopes of
Geitafjall (Greig, pers.comm.). The small weeVil,
Ceutorhynchus contractus breeds in many different
species of Crucifer (Dieckmann, 1972) but the few
modern Icelandic records, including one from Vík
(Larsson & Gígja, 1959), tend to be coastal, where the
species perhaps breeds in scurvy grass, Cochlearia
officinalis; Lindroth (in Lindroth et al., 1973) also
records the beetle from a whitlow grass, Draba
nemoralis, in southern Iceland. Both Ketilsstadir
records are post-Landnám but this weevil appears
beneath the Thjórsárhraun at Thjórsárbrú in deposits
of about 8,000 B.P. (Buckland et al. 1986).
Although the faunas become considerably more
diverse after Landnám (fig. 7), only two species of
beetle are directly associated with man. The dung
beetle, Aphodius lapponum, could not have lived in
Iceland before the introduction of large herbivores; it
first appears in the Ketilsstadir succession in sample
BRl/10, probably belonging to the eleventh century.
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