The Botany of Iceland - 01.12.1945, Side 107

THE VEGETATION OF CENTRAL ICELAND
449
the snow-ccvcring is relatively deep. The E and H percentages are
very high. Within my area of investigation this association was only
found in Víðidalur.
ii. Empetrum nigrum—Dryas octópetala—Elyna Bellardi-Ass.
(Tab. XVI. A-B, 8).
The only analysis representing this association was made near
Geldingsá. The locality is a level, stony plain by the river, so low-lying
that it is probably flooded by the river in the period of thaw. The
soil is fairly dry and sandy. The three character species dominate phy-
siognomically, but lichens of the genera Alectoria and Cetraria are so
conspicuous that the association could almost be called a lichen heath.
The biological spectrum shows high A and Ch percentages, which both
approach their maximum in the shrub heath. The H percentage, also,
is relatively high, while the G percentage approaches the minimum of
the shrub heath. The association here covers a small area and was not
noticed elsewhere.
The following table shows the mean values for the A and Ch
percentages in the shrub heath. The associations are arranged accord-
ing to decreasing Ch percentage. Associations 9 and 10, however, are
placed separately at the end of the table, since they can hardly be
regarded as belonging to the shrub heath. They are only found under
very special conditions and evidently have quite different requirements
from the other associations of the shrub heath.
Associations Ch pct. A pct.
I I 43.8° 71.2
4-5 42.26 65-99
3 36.67 64.42
7 36.20 57-50
6 33-43 72.13
2 32-94 70.44
I 32-85 57-47
8 32-5° 68.75
9 40.30 56-50
10 24.40 53-40
36-54 66.16

23-9 66.6
Mean value of all associations
The highland flora ..............