Fróðskaparrit - 01.01.1998, Page 249

FLOGSÁÐFRØÐILIGAR OG GRÓÐRARLIGAR BROYTINGAR í SAMBANDI 255
VIÐ BOTNSETING AV SAKSUNARVATNSØSKU f FØROYUM
OVARU HOYDALAR: percentages
Fig. 10. Pollen and spore diagram ofselected taxafrom the Saksunarvatn ash zone, Upper Hoydalur. Percentage
values are expressed as TLP minus alien AP. Total identifiable palynomorph concentrations exclude alien AP.
Mynd 10. Flogsáð- og grókomstrikumynd av úrvaldum taxa úr saksunarvatnsøskuøkinum í Ovaru Hoydølum.
Virði í prosentum em lýst sum TLP minus fremmant AP. í samanløgdu palynomorfkonsentratiónunum, sum kunnu
eyðmerkjast, er fremmant AP ikki tikið við.
the thinning tephra band (only 1.6 cm
thick), Salix, Calluna vulgaris, Empetrum
nigrum, Botrychium and Pteropsida have
increased representation (Fig. 10). This
pattem is evident from both percentage and
concentration data.
It seems that the tephra-fall may have en-
abled taller plants to thrive, perhaps by al-
lowing them a flowering advantage over
taxa with a lower architecture. Thus Poa-
ceae, Calluna vulgaris, Salix and Botrychi-
um seem to do well. Lamiaceae (and
! yperaceae if its decline is tephra-related)
may have suffered from growth in damper
areas where the choking effects of tephra
might be expected to have most impact,
though Caltha is not reduced. The aquatics
Myriophyllum alterniflorum and Isoetes
echinospora are not well represented any-
way, but the former taxon is reduced.
Total identifiable pollen and spore con-
centrations excluding alien AP are reduced
from 28,289 grains cm'3 at 251.4 cm, to
15,849 grains cm'3 in the spectmm immedi-
ately below the tephra layer, a figure simi-
lar to that within the top of the tephra
(16,137 grains cm"3 at 249.6 cm). The next
spectrum (249.4 cm) is further depressed to
an estimated 11,290 grains cm 3.
The apparent smaller impact at Hoydalur
may be due to the more restricted range of
habitats and topographic units around the
basin. The variation in slopes is consider-
ably less than at Hagamýra and much of the
Hoydalar pollen may derive from areas
which did not suffer from prolonged tephra
deposition. The fact that the ash layer is
considerably thinner at the Streymoy site