The Botany of Iceland - 01.12.1930, Blaðsíða 166

156
H. M0LHOLM HANSEN
forms, it will be of interest to have another system of indicators of
environment. In the present treatise the geographical distribution
of the individual species has been employed as an indicator of en-
vironment. A species with a pronounced southern distribution will
more certainly indicate a high temperature than a more northern
species. The more southern species there occur in an area, and
the more prominent the role they play, the more probable will it
be that the temperature conditions are favourable. Reversely, it
must be supposed that a preponderance of arctic species indicates
severe cold. The proportion of southern and arctic species
in an area will therefore indicate the temperature con-
ditions of that area.
In a previous chapter the species groups were dealt with in
more detail. At the outset it might be anticipated that the species
groups would be more sensitive indicators than the life-forms, and
it might be claimed that the two systems of indicators should lead
to the same result. An inspeclion of the tables will show to how
great an extent this is the case. A change of environment causing
an increase of the Ch percentage will likewdse cause an increase of
the A percentage, and numerically this increase will be greater than
the Ch increase.
Table 31 shows the life-form and species group spectra for a
series of areas in which the conditions of environment are most
clearly illustrated. The localities are ai’ranged in groups of 3 each.
The top group 1, comprises the land spectra for Denmark, Iceland,
and North Greenland, group 2 the Icelandic zone spectra for the
lowlands and the upper and lower zones of the highlands respec-
tively, group 3 various zone spectra from Vestflrðir, for the 0—
100 m zone, the 2—300 m zone, and the 3—400 m zone respec-
tively, group 4 shows vegetation spectra for snow-bare, normally,
and constantly snow-covered vegetation in the same locality, and
group 5, finallv, gives the mean values for the formation spectra
of the various classes of snow-covering. Within each group the
coldest area, a, is given flrst, the warmest, c, last.
A closer inspection of the table will show that, compared with
the b spectra, all the a spectra have a high Ch percentage, A 3 per-
centage, and especially a high A percentage, while the c spectra, on
the other hand, have a high (Ph + K + Th) percentage and (E3 +
E 2 + E 1) percentage. The amounl of H and (A 2 + A 1 + E 4)
species is relatively unaffected by changes in temperature in any