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Dr. Ralf Petercord

LWF

Bavarian State Institute of Forestry
Section Forest Protection
Hans-Carl-von-Carlowitz-Pl. 1
D-85354 Freising

Phone: +49 (8161) / 71 - 4928
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Author(s): Editorial office waldwissen.net – LWF
Editorial office: LWF, Germany
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Tracking the bark beetles

Bark beetles are capable of causing large-scale damage during mass propagation. With the help of the bark beetle monitoring program, data for scientific research is collected and important information for the forestry praxis is made available.

Buchdrucker und Kupferstecher
Fig. 1: The European spruce bark beetle (left) and the six-toothed spruce bark beetle (right) are the two species that the Bavarian bark beetle monitoring program has been observing since 2004 (Pictures: L. Borowiec, Universität Wroclaw, Pl.).

The heat wave in 2003 resulted in a mass propagation of the European spruce bark beetle (Ips typhographus) and the six-toothed spruce bark beetle (Pityogenes chalcographus). As a result, the Bavarian State Institute of Forestry (LWF) established a bark beetle monitoring program for these two species in early 2004. Up till then the beetles were only monitored at local hotspots. A region-wide and consistent surveillance of flight behavior and population dynamics of this pest was made possible with the new, uniform and consistent Bavarian wide system. Foresters and forest landowners can quickly receive information regarding the regional development of the beetles and therefore react in a timely manner to deploy appropriate counter measures.

How does the monitoring work?

Entleeren der Falle
Fig. 2: Captured insects in the bark beetle traps are emptied out and examined weekly (Picture: C. Triebenbacher).

In order to monitor the beetle, approximately 300 pheromone traps have been placed in a homogeneous raster over the entire area of Bavaria. The respective forester empties the traps weekly. On every monitoring site, four traps are used. The first pair consists of one trap each for the European spruce bark beetle and the six-toothed spruce bark beetle and monitors their population. The second pair is used to verify the results of first pair in order to avoid false interpretations from variations in catch results (e.g. antagonism, exhausted pheromones, small scale climatic variations). Additionally, trap logs are laid out in twelve forest districts. A trap log is a piece of spruce (branch, log etc.) on which bark beetle pheromones have been applied in order to promote the colonization by bark beetles. During the weekly checks of the pheromone traps the foresters also analyze trap logs in order to determine the development and vitality of the bark beetles.

The foresters can document their results in a LWF database. In addition to the catch results per trap, certain particularities can also be documented such as extraordinary by-catch plus the results from the trap logs. Furthermore, the colleagues deliver a site-specific estimation of the current bark beetle situation. The results are published on the website www.borkenkaefer.org (only in German) in the form of graphs depicting the swarm curves and maps displaying the threat per forest growth area.

For forest landowners and foresters

Bruthölzer
Fig. 3: Trap logs are a second method along side the pheromone slot traps in which the swarming and population development can be observed (Picture: C. Triebenbacher).

Every user can, objectively and free of charge, make their own impression about the emanating risk from bark beetles from the monitoring results. Thus, the forest landowner has the opportunity to undertake preventative measures in a timely manner. The website www.borkenkaefer.org distributes an extensive range of information. In this way, forestry colleagues and forest landowners can educate themselves on management recommendations from the LWF in order to keep infestation in check (advantageous timeframes, methods and assessment), or to develop control strategies (timing the processing and treatment of residual timber).

Furthermore, there is an opportunity to use the LWF newsletter service "Focus Forest Protection" (only in German). Between April and September the newsletter contains reports about the current bark beetle situation in addition to other forest protection topics.

Monitoring programs of neighboring countries

Swarm curve of the European spruce bark beetle
Fig. 4: Typical swarm curve of the European spruce bark beetle from the forest district of Heigenbrücken (year 2010):
End of April (Calendar week 17):
Flight of the parent beetles which procreate and the establish the first generation;
End of May (Calendar week 22/23):
Establishment of the first sister generation by the parent beetles;
Beginning till middle of July (Calendar week 27/28):
Flight of the first generation which will establish the second generation

Click to enlarge.

After the drought of 2003 Austria also built a similar system. An exceptional feature of the Austrian monitoring program is the expansion of the surveys to detect other bark beetles such as the large larch bark beetle, six-spined and other pine engraver beetles. The Austrian Research Centre for Forests (BFW) publishes the results and an estimate of the situation at www.borkenkaefer.at (only in German).

In Switzerland the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) publishes data at www.waldschutz.ch (partially in English) for data collected once a year regarding the European spruce bark beetle. These topics are addressed:

  • Beetle sanitation harvests in the summer months (April till September)
  • Beetle sanitation harvests in the winter months (October till March)
  • Amount of infested timber left standing
  • Sum of newly created infestation nests (beetle nests i.e. a mass of infestation with 10 or more infested trees)
  • Sum of the erected pheromone traps
  • Sum of the European spruce bark beetles caught per trap

The data is compared to the results of the previous year in order to show patterns in the development of the beetle infestation.

The conclusion for Bavaria

With the establishment of the bark beetle monitoring program of the LWF a Bavarian wide information system was constructed whose positive effects can clearly be felt. Not only foresters, but also private landowners can access comprehensive and current information. The monitoring doesn’t just detect indications at the beginning of mass propagations but also delivers important findings (e.g. the correlation between weather and flight behavior). Monitoring systems will gain importance over the course of climate change and in particularly with thermophilic (i.e. warmth loving) insect species. It is expected that especially these species will have an increase in mass propagations with an increase in temperature. Extensive changes such as these can more accurately be predicted with the help of this kind of long-term observation and, as a result, substantial damage can be avoided.

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