Full-text - Norsk entomologisk forening

210 A. Lillehammer
The bottom of the valley lies in the upper
part of the Sub-Alpine birch belt and the
tree line is somewhat higher on the northern
side of the valley than on the southern side.
The bottom of the valley and the wooded
sides are often thickly covered by dwarf
willow and dwarf birch.
Stream descriptions
The main river follows the valley in a
west-east direction. The tributary streams
run more or less at right angles to this. Most
of the streams rise at heights above 1400 m,
some from springs while others have melting
snow as their main source.
In the bottom of the valley the streams
often have a more or less dense fringe of
Salix. This diminishes with altitude, and
above 1200 m it is only present in especially
sheltered places. At and above 1300 m there
are only sporadic bushes, the main vegetation
being grass.
Around 0vre Heimdalsvann stream temperatures
lie at about 0° C during the winter,
while in the summer they may reach temperatures
of 15-18° C, although the mean is
markedly lower (Kloster, personal communication).
The pH varies from 6.1 to 7.4, but
the most common values are from 6.5 to 6.8
The Ca+ + content was from 0.5-2.0 mg/l
and Mg+ + about 0.5 mg/l.
0vre Heimdalsvatn
This lake has recently been the subject of
intensive study under the auspices of IBP.
It is 3 km long, has an area of 0.78 km 2 and
a catchment area of 24.4 km 2 • The lake is
shallow - its greatest depth is 13 m. Near the
shore the substratum is mainly stony, the
stone band being most extensive in the outlet
area. Around the inlet there is only a thin
band of stones below which sand predominates.
0vre Heimdalsvatn is usually ice-covered
from October to the beginning of June. From
January to June surface temperatures lie
between 0° and 1° C. In the latter part of
June, July, August and most of September,
temperatures generally lie between 7° and
14° C, while from October to December they
are below 2° C. The pH usually varies between
6.5 and 7.0. The Ca + + content varied
between 1.5 and 4.5 mg/l, the Mg+ + between
0.5 and 1.0 mg/l.
Stonefly fauna
In this area, 21 species have been taken.
Among the 29 species in southern Norway,
the rare Perlodes dispar, Xanthoperla apicalis
and Isogenus nubecula are absent. Amphinemura
borealis and Capnia pygmaea,
which have not been taken above the boreal
coniferous zone in southern Norway, are
also absent. In addition Siphonoperla burmeisteri,
N emoura flexuosa and Isoperla
difformis have not been recorded.
Twenty species have been taken in streams
(Table VI). Among the herbivorous species
the most common were Amphinemura standfussi,
A. sulcicollis, Nemoura cinerea, Capnia
atra and Leuctra nigra. Capnia bifrons
was also common both in the Sub­
Alpine belt and in the Low-Alpine belt
where willow is abundant along the streams.
The dominating carnivorous species of the
whole area was Diura nanseni, although the
omnivore lsoperla obscura was equally common.
There are large differences in the stonefly
fauna of the various vegetation belts.
This will be discussed later.
There are also considerable differences in
the fauna of streams which flow throughout
the year (streams 1-6) and the three small
streams (7-9) which are more or less temporary.
In the latter only Nemoura cinerea,
Nemurella picteti and Isoperla grammatica
were taken.
In 0vre Heimdalsvatn 10 species were
taken (Table VI). The most common herbivore
species were N emoura avicularis, N e­
moura cinerea, N emurella picteti and Capnia
atra. The carnivore Diura bicaudata was very
common and seems to be the main invertebrate
predator in the littoral fauna of the lake.
In Brurskardstjenn (about 1300 m a.s.l.)
6 species were taken in the lake, 5 of them
herbivores. In Blatjenn (1465 m a.s.l.) 4 species
were taken, 3 of them herbivores. The
plecopteran fauna of Bliitjenn was dominated
by Capnia atra and Diura bicaudata.
The outlets of 0vre Heimdalsvatn and
BHHjenn were richer in species than the
lakes. The outlet of 0vre Heimdalsvatn supported
12 species and the outlet of Bliitjenn
5 species. The stonefly fauna of the outlet of
0vre Heimdalsvatn consists of the lake species
and in addition lsoperla grammatica
and T aeniopteryx compacta. In the outlet of