Full-text - Norsk entomologisk forening

Norwegian stoneflies Il 225
poorest biotopes had clear dominance over
two species. The decrease in the number of
specimens between stations 3 and 4 where
Salix showed a marked decrease, was also
clear.
In conclusion it can be stated that there is
a reduction in stonefly species and numbers
when there is a reduction in the amount of
allochthonous matter from deciduous trees,
mainly Salix, and a fall in temperature.
Eastern area
This area embraced the Sub-Alpine, Low­
Alpine and Middle-Alpine belts of central
Norway.
The results of zonation investigations III
area 1 indicated that the main reduction III
species was correlated with the reduction in
Salix vegetation along the streams.
To obtain further information concerning
this trend, studies had to be carried out in
different faunal areas, such as eastern Norway
and northern Norway. One of the most
convenient areas for such a study was 0vre
Heimdal. Six streams in 0vre Heimdalen
were chosen and the work was carried out
during the period 1969 to 1972.
Stream descriptions
The lowest parts of the streams are situated
in the upper part of the Sub-Alpine belt (at
about 1060 m a.s.l. where there is a very
dense fringe of dwarf willow mixed with
birch along the stream (Fig. 18)).
The substratum is unstable, and there is a
mixture of stones of various sizes and gravels.
There is a fair amount of organic allochthonous
matter.
The upper edge of the Salix belt is at an
altitude of 12-1300 m a.s.l. where there is no
continuous fringe, but scattered low bushes
at especially sheltered places. The main vegetation
is grass. The substratum is more stable,
the stones are usually larger and there is less
allochthonous organic matter in the streams.
At an altitude of about 1300 to 1400 m
a.s.l. the only vegetation is grass (Fig. 19).
The substratum is a mixture of large stones,
gravel and small stones, and it is unstable.
There are only small amounts of allochthonous
matter.
At altitudes above 1400 m even the grass
cover becomes patchy. The substratum is
Fig. 18. 0vre Heimdal, Stream Flybekkin In the
Sub-Alpine belt.
Fig. 19. 0vre Heimdal, Stream Flybekkin In the
Middle-Alpine belt.
similar to lower altitudes and only small
amounts of allochthonous matter were present.
Stonefly fauna
As in the west (area 1), the main decrease
in species took place in the same area as the
main reduction in Salix vegetation along
streams, where the number of species dropped
from 20 to 11. Above this the reduction continued,
and at about 1400 m only Arcynopteryx
compacta, Isoperla obscura, Amphinemura
standfussi and Capnia atra were present.
The only species numerous at this height
was Arcynopteryx compacta (Table XVI).
A comparison of herbivores, carnivores and
omnivores, according to Brinck's (1949) classification,
showed that the reduction in species
was largely among the herbivores. The
fauna above 1400 m consisted of one carni­