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Competence Network Climate Change, Risk Management and Transformation in Forest Ecosystems

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Forest Research Institut Baden-Württemberg (FVA)
Department of forest economics

Wonnhaldestr. 4
D-79100 Freiburg

Tel:  +49 761 4018 231
Fax: +49 761 4018 333

Article

Author(s): Hansjochen Schröter, Holger Veit, Jutta Odenthal-Kahabka
Editorial office: FVA, Germany
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Alternative Control Measures for Wood and Bark Boring Insects

Alternative control measures were intensively discussed in the context of tense forest protection situations during the years after the storms in 1990 and 1999). The target was to reduce the already low amounts of insecticides used even further. The basic approaches and the experiences applying them are described here.

Trap trees and mass trapping with pheromone traps

Pheromonfalle

Fig. 1: Effective use of bark beetle traps is only possible with a massive labour effort. (Photo: FVA, Dept. for Forest Protection)

  • Both measures are basically suitable means to influence infestation progression on a local level.
  • However, they are both not fit for population regulation during population growth stage and peak in the main damage areas.
  • Trying to reduce population densities of Ips typographus after large-scale storm calamities requires a massive personnel and material effort. This can hardly be achieved in today’s business structure. Additionally, it is out of all proportion to the benefits gained when compared to available alternatives. Successful realisation of these measures requires personnel and technical capacities to be flexibly deployable at all times as well as a high degree of caution, diligence and experience.
  • The measures are only suitable for controlling localised calamities or for accelerating the demise of large-scale calamities as one of many measures used for the local protection of vulnerable stand edges.

Wet storage

Wet storage is expensive. It only makes sense when used to relieve the timber market. Short-term storage aiming solely at killing beetle broods as a measure of forest protection is not justifiable from a commercial point of view.

Nasslagerplatz

Fig. 2: Wet storage. (Photo: R. Willmann)

  • It can be assumed that "white stages" (eggs, larvae, pupa) are killed if irrigation is started immediately. Flying and further breeding can be expected if adult beetles are present, putting adjacent stands at risk. Furthermore, logs in which maturation feeding has already taken place will loose a lot of bark when handled and during transport. Large proportions of the untreated bark containing the brood and/or adult beetles will therefore remain in the forest. This can result in a very low degree of effectiveness and does not justify the high costs involved in wet storage.
  • Therefore, wet storage is best for infested trees that were detected early, logged immediately and dispatched straight away. A consistent and efficient logistics chain is needed here.
  • Wet storage can not be recommended as a standard forest and wood protection method in the event of bark beetle calamities.

Film wrapping

  • Small-scale tests in a hothouse showed that the mortality rate of wood and bark boring beetle species is very high inside the wrapping. However, individual beetles repeatedly managed to bore through the plastic film.
  • Infested and non-infested timber should never be stored together inside the same wrapping. The tests showed that the beetles react to a deterioration in living conditions by leaving their burrows and infesting other logs inside the wrapping.
  • Conditions demanded in terms of timber quality, brood development stage, and thus the available time frame, correspond to those given for wet storage. Hence the same problems and consequences can be expected from a forest protection point of view.

Removal of susceptible or infested logging residues

Controlled burning, mulching, etc. is only justified if…

  • large amounts of infested material accumulate near adjacent vulnerable stands!
Fängischer Schlagabraum

Fig. 3: Hazard or not...? (Photo: FVA, Dept. for Forest Utilisation)

Non-infected material lying close to vulnerable stands must be checked for infestation regularly if…

  • larger amounts accumulate,
  • the residue contains larger diameters,
  • and/or is located predominantly in shadow!

Logging residues dry out relatively quickly and/or are a much less hazard if...

  • the residue only contains small diameters,
  • and/or is exposed to intensive solar radiation,
  • the bark was removed and/or crushed by a harvester’s processor head,
  • branches and twigs are left on treetops to maximise the evaporation surface area,
  • the bast fibre turns into a brownish colour (the bark is comparatively hard to remove)!
  • Treetops and residual timber can alternatively be “striped” (partly debarked, peeled in strips), but this labour intensive work and therefore high costs, must be balanced against the benefits.
  • Past experience proved motormanually cutting the residues into 30-50 cm pieces was largely ineffective!

Instructions for controlled burning of logging residues

  • No burning during times of atmospheric inversion, wet weather, strong winds or long droughts!
  • Use dry wood for kindling.
  • Do not use petrol, waste oil or car tyres to light or maintain the fire (illegal in Germany).
  • Fires inside the forest should burn at a high heat and as quickly as possible.
  • Do not misuse the fire to dispose of your waste.
  • Keep enough distance to surrounding trees.
  • Do not light fires on steep slopes! Burning material could slide down.
  • As a precaution, the local/ regional forest authorities and fire brigade should (or must, depending on local laws and regulations) be informed about planned controlled burnings (time and place) to avoid unnecessary (and possibly expensive) fire fighting operations.
  • Keep suitable fire-fighting equipment on hand (water buckets, fire extinguishers).
  • Permanent supervision of the fire by at least two people (at least one of whom should be an adult).
  • Do not leave the site before fire and embers have gone out completely. Remnants of glowing embers must be entirely extinguished.
  • Pile up residues only immediately before burning, as birds and small mammals might otherwise take shelter inside slash piles.
  • Maximum height of the piles: approx. 3.5 metres.

Information