Northern Wisconsin advertiser. [volume] (Wabeno, Wis.) 1898-1925, 1901-09-05
ARCTIC VEGETATION.
Light compensates For Inadequate
Warmth.

Prof. j. Wiesner of Vienna univer-
sity, who for some years has been
engaged in researches on the require
ments of plants in the matter Of
light, has come to the following con.
illusions with regard to the plants
of the Arctic regions. The demonstra.
ton previously put forward by him
with regard to low and middle
ATTITUDES, that with the increase of
latitude the light requirement of
plants also rises, has been shown, by
observations made in Norway and at
advent bay, Spitzbergen, 1912 north
latitude, to apply equally to sub-arctic
and Arctic regions. The reasons for
this marked need of light are the low
temperatures which prevail at the
vegetative period, the want of heat
being made up for by excess of light,
the amount of which must therefore
increase with the decrease of tenn
perature. 1t thus comes about that a
limit is set to the migration toward
the pole of bush and tree vegetation
less by the cold of winter than by the
contantly increasing need of light,
which can, of course, be less and less
satisfied. AS rule, the plants of the
far north can stand but a small
diminution of their quantum of light,
such as is caused by the interrogation
of the suns rays through the con-
figuration of the country.
DIR. Peucker's researches on noun
tain shadow have shown how the
amount of light required can be laid
down with precision in each particular
case. The intensity of the direct sun
light to which Arctic plants are ex-
posed is very slight, for it only be-
comes perceptible when the sun
reaches an altitude of Is degrees
above the horizon, whereas in the
most favorable case, on June 81, the
sun only attains, at Advent bay, an
altitude of 80 to 35 degrees. Direct
sunlight here at best reaches the
strength of the light radiated from
the whole expanse of the sky, the So
called "diffused light" so that the
whole illumination available for polar
plants is at most double the amount
of the diffused light. The high Alpine
plants of mean ATTITUDES, on the con-
trary, enjoy an amount of illumination
which may be estimated at a max
imum of at least four times that due
to the diffused light, the sun reaching
a midday altitude in summer of Sc TO
SO degrees. These differences result,
as BONNER has shown, in considerable
variations in the organs of plants Of
like species, which occur both in high
Alpine and high Arctic regions. In
middle ATTITUDES the effect of aspect
on vegetation is very striking, the
northern slopes Of mountains being
often bare of plants. But in view of
the much nearer approach to COM
plete circuit round the horizon made
by the sun in Arctic attitudes it is
easily seen that this influence is less
felt there than anywhere.
OF much interest, lastly, is the de-
monstration of the influence exercised
by differential lighting on the form Of
trees, the low angle at which light Is
received especially favoring the
pyramidal shape in Arctic ATTITUDES,
though this is by no means deterimen-
tai under the more nearly vertical
lighting of low ATTITUDES. The cyp-
resses Of the south are, in fact. pro-
tected by their form from the in
furious effects of vertical sun, while
the same form enables the frs, pines
and white pOplars of Norwav and
Sweden to make the most of the
horizontal rays Of the northern sun.
British Geographical Journal.