Heft 14 - Nationalpark Bayerischer Wald

Bark beetle outbreak
in the Bavarian Forest National Park
In 1983 and 1984 hurricane like storms uprooted
countless trees in the Rachel-Lusen area of the
Bavarian Forest National Park, especially spruce
forest stands on swampy an weak soil in the
lowland spruce forests and to a lesser extent, the
mountainmixed forests of the park. The total area
of disturbed forests was 173 ha. Only 14.3 ha of
the disturbance occured in the mountain spruce
forest. Over all, halfthe affected areas were in the
Park's no management zone and, as such, these
areas were left alone. Due to the huge amount of
breeding material, the bark beetle was able to
reproduce quickly and populations became large
enough to attack and kill healthy trees. By the
beginning of the 1990's bark beetle activity had
declined and the total area of spruce stands being
attacked began to decrease slowly. However, in
1992 beetle activity sudden Iy i ncreased aga i n a nd
has since remained on a high level.
Aerial photographs have been taken annually
since 1988 and allow for the precise mapping of
old dead forest stands and for the effect of bark
beetle outbreaks to be documented. The most re­
cent aerial photos were taken on the 24th September
2000. Analysis of these photographs indi­
cates that bark beetle populations remain high.
In the year 2000, the total stand area killed by the
beetle increased by 605 ha. This is the second
highest peak since the start of monitoring activities,
the highest being in 1996 with 827 ha of
forest stands killed, the total area has now increased
to 3.712 ha, equivalent to 29 % of the
Rachel-Lusen area. The mountainous spruce
forests are the main affected areas within the
Park with 85 % ofthese forests hav,ing been killed.
Large complexes of dead trees can also be found
at other elevations, however the proportion of
killed trees present is lower than in the mountainous
spruce forests. Up to 36 % of mountain
mixed forests stands and 11 % of lowland spruce
forest stands have also been killed by beetle
activity.
A 500 m strip of forest in the National Park is
subject to active forest management in order to
protect private forests along the borders of the
Park. Active forest managment is also carried out
in all areas of the Falkenstein-Rachel area, with
exception to 1.160 hectares of core zone. The
highest amount of so-called "bark beetle timber
cut" was 60.000 m' in 1998. Since then "bark
beetle cut" has decreased to ha If of th is a mou nt.
The distribution of clear cuts caused by forest ma­
nagement in the margin zone, provide further
proof of the effectiveness of bark beetle management.
In 1997 most of the clear cuts were distri­
buted around the margin zone. However since the
year 2000, management activities have been
mainly undertaken close to the core zone. Since
then, evidence of bark beetle damage has de­
creased as the distance from the core zone
increases.
It was assumed that the weather plays an
important role in the population dynamics of the
bark beetle and as such, weather data from the
last 20 years was collected and analysed. The data
relating to mountainous spruce stands was taken
from the Arber weather station, whilst, data
relating to the lowland spruce forests was taken
from the Klingenbrunn-Bahnhof weather station.
This data showed that the decline of the bark
beetle in the early nineties correlates to a reduction
in potential swarm days during this period
(potential swarm days occur when the tempera­
ture reaches 20 ' Cl. The relationship between the
average temperature in the vegetation period and
the rate of change in the area of the dead stand,
when compared to the previous year was even
more significant.
The dynamics of insect populations in respect to
its major influencing factors (i.e. habitat, natural
enemies, competition and weather patterns) were
analysed on the basis of these latest research
resu Its.
It is clear that weather patterns and habitats "are
the most important regulatory factors on the
dynamics ofthe bark beetle populations.
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