If the volumes of timber accumulated during big storm events can not, or shall not, be brought to market straight after processing, a suitable conservation method has to be applied. Conservation of the timber quality is the main objective. Experiences with handling storm damaged timber after "Vivian and Wiebke" in 1990 and "Lothar" in 1999 show that "Relief of the Timber Market" and “Maintenance of Timber Prices” are of course desirable additional aims, but can only be realised if the forest owners and forest companies show solidarity.
The conservation of timber includes all actions to conservetimber quality including protecting it from chemical, physical, and biological decomposition. Technically, there are a variety of conservation methods available. the main deciding factor is timber moisture: it has to be either brought up to over 120%, and be kept at this level, e.g. by wet storage, or dried rapidly to under ~30% moisture content (fibre saturation range), e.g. by storing under drying conditions.
Figure 1 shows the most commonly used conservation methods. Special methods, like covering timber piles with straw, soil or lime mixtures as well as underground storage in mines or tunnels, are not included in these leaflets. There is no operational experience with these methods, and so far they have only been applied in experimental or exceptional cases.
The first part of table 1 gives a quick overview of storage possibilities for tree species and assortment groups.
The second part shows suitability of conservation methods by type of tree damage (broken/thrown). These can be combined with the tree species in part one.
|Grading class||Wet storage||Storage under oxygen exclusion (limited capacity)||Dry storage of debarked logs||Life conservation|
|Spruce/fir logs||L 2a – L3a||**||*||0||0|
|L 3b – L6||**||*||0||0|
|Larch logs||(*) – 0||-||**||-|
|Douglas-fir logs||(*) – 0||-||*||**|
|Beech (high quality)||L 5 – L 6||*||**||-||0|
|Beech (medium quality)||L 4 – L 6||*||*||-||0|
|Oak (high quality)||(*) – 0||0||0||*|
|Oak (medium quality)||(*) – 0||0||*||*|
|Windthrown tree without sufficient contact between roots and soil||[* / 0]||-||* / 0||-|
|Windthrown tree with sufficient contact between roots and soil||* / 0||* / 0||* / 0||**|
|Broken tree||-||-||[* / 0]||-|
|Lifted, bent tree without sufficient contact between roots and soil||[* / 0]||[* / 0]||* / 0||-|
|Lifted, bent tree with sufficient contact between roots and soil||* / 0||* / 0||* / 0||**|
|Rating||Very Good||Good||Suitable||Unsuitable||in brackets [ ]|
|**||*||0||-||Suitability dependent on moisture content of timber at the time of storage|
|Tab. 1: Overview of storage methods.|
|The partly better rating in parentheses ( ) indicates that different forestry offices in Baden-Wuerttemberg implemented this storage method successfully after "Lothar". However, wider experience and further recommendations are lacking.|
The various possibilities for timber storage after calamities are described in individual leaflets. Besides detailed information on construction and operation, they explain advantages and disadvantages of the methods. Short-term storage alongside forest roads (applicable for "normal" timber loads) is also included, even though this method is unsuitable for longer storage terms, as the moisture content of the timber remains within the critical range >40% and <100%. The increased risk of wood degradation caused by fungi and insects makes quality conservation impossible. Softwood in particular can only be protected against infestation by wood-boring beetles by applying insecticides. Capacities for storage alongside forest roads are also limited and under certain circumstances might obstruct other salvage logging operations. Storage of timber in standing water bodies effectively prevents the logs drying out and infestation by insects, but it is prohibited in Baden-Wuerttemberg, under the administrative regulation on "Wet storage of roundwood" for the following reasons:
Suitable open water bodies are relatively rare. Water authorities usually do not grant permits, or only do so under strict conditions.
Increased insertion of matter into the water bodies reduces their ecological functions considerably. Other usages become impossible during the storage period.
Fallen bark accumulates on the bottom of the water body and decomposes only very slowly. This puts other usages at on-going risk.
Parts of the logs protruding above the water surface have to be protected against drying out and therefore must be additionally irrigated.
Losses result from timber sinking into the bottom of the water bodies.
Removing the soaked timber from storage is expensive.
The following points should be considered when choosing a method of conservation:
Choice of conservation method
- Type of storm damage (broken/thrown)
- Tree species and assortments and their suitability for storage
- Expected quantity of sales and sales markets
- Expected duration of storage
- Availability of suitable sites (in particular for wet storage)
- Matters of permits/regulations (in particular for wet storage)
- Availability of manpower and financial considerations (see below)
Map out a strategy outlining the storage of timber considering the volume of damaged timber, size of the area affected by the storm and absorptive capacity of the market.
Benefits of the storage have to be weighed up against potentially incurring costs.
Using storage methods with high investment costs and long storage duration in particular, incur high financial costs, which initially have to be paid for by the forest owner. The movement of timber prices after storm events is uncertain and prices may possibly be put under further pressure through subsequent events (such as bark beetle calamities). It is therefore not unlikely that the additional proceeds from the stored timber will only partly cover the expenses of cost intensive storage methods. Subsidies for the storage of storm-damaged timber might compensate for this.
Quality preservation and control
Improper storage has timber quality risks: Infestation with insects, decomposition through fungi, and development of stains and discolourations.
The time between salvage logging and storage has to be kept as short as possible. For quality preservation, during wet storage in particular, green timber should be put in storage right away (not later than two weeks after cutting), and irrigation started immediately. Salvage logging must be stopped if there is not enough capacity for transport or storage. Dried out or low-quality timber should not be put in storage.
Continuous monitoring of timber depots and the quality of stored timber must be carried out during the whole storage period. Irrigation systems at wet storage depots have to be checked daily. If timber is stored under oxygen exclusion, the composition of the inner atmosphere has to be checked.
Measuring the moisture of timber in life conservation intended for wet storage can help decide whether putting the timber into wet storage still makes sense, or if it needs to be brought to the market immediately.
- 2004 "Technical guide on harvesting and conservation of storm damaged forests", FAO, Sustainable Forest Management (SFM) Toolbox, Link
- Ittel-Reinlassöder, I.(1991): Überwachung der Wasserqualität an Nasslagerplätzen. AFZ 5/1991, S. 248-251.
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