The Botany of Iceland - 01.12.1945, Blaðsíða 155

THE VEGETATION OF CENTRAL ICELAND
497
it was made at an altitude of c. 850 m. Above this altitude Grimmia
dominates physiognomically, in other words, the brekkur formation is
replaced by the Grimmia heath. Now the number of species and the
total of points dccrease considerably, and this continues to the top of
the mountain at c. 1000 m altitude, where the highest lying analysis was
taken. Up there two formations have alternately the superiority, melur
occurring in the most exposed places and Grimmia heath where there
is some shelter. Analysis 1 o was taken in a melur area on Loðmundur.
The biological spectra show distinctly that the A percentage increases
with increasing height until reaching 100 in analysis 10; a the same
time group A 3 only increases here, since groups A2 and Ai almost
disappear. Of the southem groups E3 indeed persists with a very low
percentage up to an altitude of c. 800 m. Then group E4 is the only
one of the southern groups present until it, too, entirely disappears in
analysis 10. The life-forms show somewhat more varied conditions. The
Gh percentage, which was fairly constant in the first four analyses,
then increases considerably, to attain its maximum in analysis 10 at
an altitude of well over 1000 m. It is somewhat higher in analysis 8
than in the nearest analyses, but this analysis was made in an exposed
locality which was more like the melur than the Grimmia heath. The
H percentage shows a constant decrease from analysis 5 at an altitude
of c. 800 m; up to that altitude it was about 50, but then decreases
strongly until the hemicryptophytes have almost disappeared in analysis
xo. The geophytes seem to be almost indifferent to the height when the
height with which we are concerned here has been reached. The G
percentage ranges between 15.8 and 22.2. It is the more peculiar that
it suddenly increases to 47.6 in analysis 9 without any particular cause
of this being observable. The occurrence of the therophytes is ver)'
irregular. These results may be summarised as follows: The Ch per-
centage is altogether high above an altitude of 650 m and increases fair-
ly regularly with increasing altitude. The hemicryptophytes dominates up
to c. 800 m, and up to that altitude the percentages are subject to small
fluctuations, but then they decrease and show a tendency to disappear
entirely at great altitudes. The G percentage is altogether low, but
shows no tendency either to decrease or increase with increasing alti-
tude. These figures show a fairly good agreement with the flora spectra
computed by M ö 1 h 0 1 m H a n s e n for the different altitudinal
zones.