The Botany of Iceland - 01.12.1930, Síða 28

18
H. M0LHOLM HANSEN
zones on the other hand. The above-rnentioned facts majr, however,
be utilised to fix one biological line of demarkation in Iceland, viz.
the 20 p. c. Ch biochore. Tlie lowest zone, the 300—400 m zone, has
a Ch percentage of 20.1. The Ch percentage in the lowlands is
below 20, and as it is a rule that species decrease in number as
we go upward, while only a few or no species are added from
above, the 20 p. c. Ch biochore may with fair accuracy be put at the
lower limit of the zone, i. e. at c. 300 m above sea level.
If we compare the position of tlie 20 p. c. Ch biochore in Iceland
with the position of this line in other regions, we shall find very
good agreement. In Scotland, according to Raunkiær (1908), the
20 p. c. Ch biochore lies at a height of c. 800 m above sea level, and
in the Faeroes at c. 500 m. In Greenland only the southernmost
part, 61—60° N., lies south of the 20 p. c. Ch biochore. In other words,
here the line has come dowm to sea level. Hence the position in
Iceland of the 20 p. c. Ch biochore at an altitude of c. 300 m is in
very good agreement with facts in the surrounding countries.
That Ch is the life form best adapted to the Icelandic climate
will also appear from the lists in another wray. It is clear from
the way in which the spectra are calculated that the rarer species
will easily come to dominate too much. This error may, however,
be reetified by comparing the spectrum formed for a series of zones
in the usual wajr with the spectrum which may be formed from
the total of the notes for all zones. Below in table 3 this has been
done for Iceland as a whole, for the highland tracts between 300
and 800 m, and for the tracts betwæen 800 and 1200 m. It will
appear from the table wilh all desirable plainness tliat Ch showr
the best adaptation, H are indifferent, and Pt, F, HH and Th show
the poorest adaptation to the Icelandic climate. The geophytes
present interesting facts. In the lowdands they are best adapted to
the climate, in the highland tracts between 300 and 800 m they
are indifferent, while above tlie 800 m curve, similarly to H, they
thrive badly.
Though we must thus suppose from the above that Raunkiær’s
life forms wrould afford a convenient basis even for a more thorough-
going investigation of the tlora and vegetation of Iceland, a classi-
fication of the flora according lo other viewpoints will always be
of interest. Hence I have also divided the flora into groups according
to the distribution of the species in Europe and the adjacent arctic