The Botany of Iceland - 01.12.1930, Blaðsíða 137

STUDIES ON l’HE VEGETATION OF ICELAND
127
Possibly the depression of the Ch percentage in Zone IV may
be referred to similar circumstances.
If we compare the A percentage and the Ch percentage in the
scale of moisture, both series are seen to take a corresponding
course with a relative minimum in Zone IV. Thus the depression
may perhaps also be due to the temperature conditions whicli are
more favourable to the vegetation in this zone than in those above
and below.
The hemicryptophytes are peculiar to the upper, drier part
of the scale of moisture with perhaps a slight indication of a rise
from Zone I to Zone IV. From this zone onward there is, at any
rate, a strong decrease. The maximum of the hemicryptophytes in
the moderately moist area which coincides with the relative rnini-
mum of the chamaephytes is most pronounced in the highland
tracts. The hemicryptophytes dominate more in the lowland than
in the highland formations, and of the lowland formations those of
the south country are more abundantly provided with H than those
of the north country. Thus, in contrast to the chamaephvtes, the
hemicryptophytes seem to thrive best in a moderately moist envi-
ronment of favourable temperature. This appears with even greater
distinctness in the distribution of the species, as is sufficiently
evident from the biological spectra in table 8 for the heath and mo
vegetation, in contrast to the vegetation of the littoral meadows and
the grassland.
The therophjHes play no verjr great part in the composition
of the vegetation in Iceland. Thej' occur most abundantlj' in the
relatively continental parts of Iceland, the highlands and the north
country; in the rainy soutli country they hardljf occur at all in the
typical formations. In the north country they occur more abun-
dantly in the lowlands than in the liighlands.
In the scale of moisture Tli attain two maxima, one in Zone I
(melar), and one in Zone IV (jaðar). In the part showing the grealest
moisture they do not occur at all. The rise in Zone IV is of spe-
cial interest: for the individuals it is most marked in the highland
series, for the species it is even more marked than for the indivi-
fiuals, as shown by the biologieal spectra of the vegetation of llie
httoral meadows and the grassland in Vestfirðir. The Th per-
centage for these two types of vegetation which correspond to the
jaðar vegetation, is 15—16, for the lieath and mo vegetation it is
°nly 1—8.