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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): J. Odenthal-Kahabka
Editorial office: FVA, Germany
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Timber Storage – Life Conservation

Life conservation of individual trees or whole stands is not a method of conservation in the strict sense of the term. It is rather an instrument to preserve timber quality and coordinate salvage logging operations over an extended period of time after calamities.

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Sturmgeworfener Baum mit ausreichend Wurzelkontakt
Fig. 1: Windthrown tree with sufficient contact between roots and soil.

Life conservation provides the possibility to differentiate between different levels of urgency of salvage logging tasks. A priority list can be compiled. Loss of a certain degree of timber quality is accepted in any case and is not avoidable. The method is not applicable for perennial conservation.

Method

Life conservation means that pushed or thrown trees are left for a certain period of time in order to direct workforce capacities to stands with higher salvage logging priority.

Temporarily delaying the cutting of such trees can maintain the tree’s water balance and therefore keep it alive. Drying out of the wood is slowed down, and the tree’s natural defences are used to prevent, or at least delay, infestation with insects and fungi.

Advantages

  • Applicable directly without prior processing.
  • No technical equipment is needed.
  • Cheap and easy to realise storage method enabling the forest company to use the available workforce in damaged

Disadvantages

  • As the water supply is restricted, infestation with insects and fungi is more likely than in trees with complete anchoring.
  • Changes in moisture within the tree can not be influenced. Success of the method depends on climatic conditions.
  • Life conservation is temporary. It should not be applied for longer than two years/vegetative periods, even for tree species rated “very good” in the table below.
  • Life conservation of spruce in particular depends on the forest protection situation of the surrounding area. Continuous beetle monitoring is therefore essential (see Fig. 1 below).
  • The forest protection situation is less critical for forests with higher proportions of fir and Douglas fir. In fir or Douglas fir stands, longer storage periods are possible without a large reduction in quality and high risk of beetle infestation. Still, two vegetative periods should not be exceeded.
  • High monitoring input and experienced and cautious staff (forest guards) are needed. Immediate action is needed if risks to forest protection arise.

Preconditions

  • Anchorage of the root plate.
    • Most important precondition: sufficient contact between roots and soil. The root plate should only be lifted slightly. At least 20% (preferably 30%) of the roots should still be anchored in the ground. If the root plate stands vertically and only a few roots are still connected to the ground life conservation will not be successful. The trees die off in a short time.
  • Storage location
    • Preferably shady locations on northern slopes. Individual thrown trees are advantageous. Spruce trees with shallow root plates on sites with stagnant or alternating moisture levels, as well as sites with high proportions of red rot infection, are unsuitable for life conservation.
  • State of the tree’s health
    • The trees need to have a green, intact crown and must not show any great bark damage. Only stands and sites with low proportions of broken timber are suited for life conservation.
  • Forest protection situation
    • For successful life conservation, of spruce in particular, the present bark beetle population (i.e. the population which existed before the calamity) should be as small as possible.
  • Monitoring and documentation of beetle infestation on storm damaged sites
    • Checking storm damaged sites regularly for beetle infestation and documentation of the findings is fundamental for successful life conservation. Forest companies have to be able to recognise increasing risks in the forest protection situation at an early stage and react accordingly. Delegation of this task to a specialised forest guard at the district level is highly recommended and has proven to be very useful.

Life conservation or salvage logging?

Decision guidance
Fig. 2: Decision guide and flowchart for life conservation (Illustration:
Forest Research Institute Baden-Wuerttemberg, Department for Forest
Protection, modified).

Suitability of tree species

Individual tree species are suited for life conservation to varying degrees:

Tab. 1: Tree-suitability
Species/assortment Suitability Storage period no longer than Vegetative periods
Douglas fir Very good 12 (– 24) months 2
Oak Very good - Good 12 (– 24) months 2
Spruce/fir Good - Suitable 12 (-15) months (spruce: risk of blue staining) 1 vegetative period/2 winters
Pine Good - Suitable 12 months (risk of blue staining) 1
Beech Good - Suitable 6 (- 12) months 1
Mixed hardwood Suitable N/a. Risk of blue staining. -
Larch logs Unsuitable -   -

Experience so far

Eastern / Northeastern slope
Fig. 3: Although it is an eastern / north-eastern slope, there is a risk of drying-up.
  • The study mentioned below shows that life conservation on moist sites with good water supply produces better quality sawn timber than on dry sites. However, after "Lothar" there were occasional good experiences on drier sites.
  • Individual or scattered wind thrown trees on shady sites seem to be better suited for life conservation than entirely thrown stands, but this could not be proved unequivocally in the study mentioned below.
  • Experiences hitherto show that stands on northern and northeastern slopes are better suited for life conservation than southern, southwestern or western slopes and plains. More recent experiences indicate that spruce trees, which were thrown downwards on northern/eastern slopes, were at higher risk of insect infestation and loss of timber quality. The reason for this phenomenon seems to be drying out of the root plate, as the underside of the root plate is exposed to strong solar radiation.
  • Studies on life conservation after the storms “Vivian” and “Wiebke” in 1990 in Rheinland-Pfalz showed the suitability of different tree species (Eisenbarth, 1995 and Bücking, Eisenbarth and Jochum, 1997).
  • The results indicate that life conservation can be recommended for spruce and pine thrown during winter for up to one year after the storm event. According to the authors, preconditions are low proportion of broken trees, normal to low bark beetle population and preferably a low proportion of damaged bark (no extreme damage).
  • Life conserved trees from moist sites with a good water supply showed better sawn timber quality than trees from drier sites. The outcome of the study did not clarify to which extent individual or groups of thrown trees need to be processed prior to entirely thrown stands. In any case, salvage logging operations should be completed before swarming of forest insects in the second vegetative period after the storm.
  • The study also included tests on life conservation of Douglas fir, oak and beech. Due to differing basic conditions and a small sample size, the results for Douglas fir are not conclusive, but experiences are overall very positive. According to the study, even life storage durations of 5 years did not have any negative effects on the quality of Douglas fir roundwood and the sawn timber produced from these trees.
  • Life conservation can also be applied to preserve timber values of oak after calamities, as long as the duration does not exceed one year. Compared to piled storage, life conservation clearly showed better results.
  • Good suitability of beech trees for life conservation was found where the trees were thrown during winter storms and were kept no longer than the following vegetative period. Furthermore, the results showed that the loss of quality is higher on openings than under shelter, where losses were marginal during the first year.

Literature

  • Eisenbarth, E. (1995): Schnittholzeigenschaften bei Lebendlagerung von Rotbuche (Fagus sylvatica L.) aus Wintersturmwurf 1990 in Abhängigkeit von Lagerart und Lagerdauer. Mitteilungen aus der Forstlichen Versuchsanstalt Rheinland-Pfalz Nr. 33/95, 211 S.
    Mahler, G.; Schröter, H.; Seemann, D.; Wurster, M. und Textor, B. (2000): Lebendlagerung muss ein Teil der Strategie werden! AFZ - Der Wald 9/2000 S. 452-453.

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