Timber Storage – Log conservation under Oxygen Exclusion
The logs are packed in air-tight,
usually silage film material. The still living wood cells use up the oxygen
inside the packing. Thus, an atmosphere poor in oxygen is created, in which
neither wood destroying fungi nor insects can survive. To secure a successful
conservation, the oxygen content within the packed stack has to be controlled
regularly. After use, the silage film can be recycled or burned.
Experiences so far
Conserving the quality of valuable
assortments by wrapping them in foil was already attempted after “Wiebke” and
“Vivian” in 1991. Encouraged by these good experiences, more than 40,000 cubic
metres of spruce, fir, Douglas fir, pine, and beech wood was put into storage
after “Lothar” in 2000. Some packages were rejected by the manufacturers due to
reduced quality (increased crack formation in beech, wood discolouration,
blueness and red stripes and sporadic brown stains and in spruce and fir
respectively). Nevertheless, all so conserved timber could be used as was
intended at the time of rolling in. As these phenomena were not known from previous
studies, it is assumed that the deterioration of quality can be put down to the
fact that the timber originated from salvage logging and the (in part) extended
time span between cutting and rolling in.
- Well protected against insect and fungus infestation;
- Longer storage duration possible, independent of weather, climate, and
availability of water;
- Especially applicable
if wet storage is not possible.
- Complex method, high monitoring
- Damages to the foil caused by
mice, vandalism, and wind may involve expensive repairs;
- Due to the high investment cost,
the conservation method is more suitable for valuable logs than as a widely
used standard procedure;
sites are not suited for foil conservation. Best results are achieved on flat,
windless locations with firm ground conditions.
- Green, sound soft- and hardwood logs (long and short) can be considered
for conservation in silage film, mainly high quality assortments. To reduce
packing costs, homogenous lengths are necessary, and packing the logs compactly
- Standard silage film
- Trained staff
- Drivable depot sites of sufficient size
- Suitable machinery to move the logs
- Two welding devices for sealing the airproof silage film cover
- A measuring device for controlling the conservation success
- The method can be applied on sites with firm ground and good transport
connections and if possible, in areas which are not highly frequented for
recreational use. Especially suitable are paved, concreted or stone paved
timber depots of wood processing industries.
- Exposure to wind may lead to
wind-induced damage to the foil (breaks and rips).
- Grasslands are usually not suitable, as lorries can’t drive on them
after rainfall. Also, the stacks might sink, with their underlying foil, into
the wet ground, making it impossible to heat-seal the underlying foil to the
cover. Once the stacks are sealed, the sinking movement can lead to cracks in
- Mice are common in grasslands and can cause a lot of damage.
Synthetic grids can help here.
- Vandalism has occurred repeatedly in the past.
- The timber has to be protected from air influx from all sides. First, a
double layer of silage film is laid out. To avoid damage, the ground has to be
cleared of stones and branches.
- A base layer of cross logs is then placed with utmost care onto the
foil. Crane handling should only be done by experienced staff.
- After stacking the timber, the edges of the logs on the top layer have
to be chamfered and branches cut off neatly to avoid damage to the covering
foil, which can then be drawn over the stack.
- The base and cover foil have to be clean and dry when heat-sealing them
- Finally, small bands of silage film can be wrapped around the base of
the stack for additional protection.
- Stacks should be controlled daily. Damage should be repaired
immediately. Even small variations in the gas concentrations in the inner
atmosphere can affect or prevent success.
€ 7.50 to 12.50 per cubic metre
roundwood, depending on stack size and design and practice of staff. This
includes material and personnel costs. Additional costs for transport and
possible leasing costs for storage sites are not included. Costs arising during
the storage period for repairing damage (through wind, vandalism, mice,…) are
incalculable. They can considerably increase total costs.
Silage film is available in various
sizes from cooperative agricultural suppliers. 16 m wide film costs approx. €
3.30 per running metre (exclusive of VAT).
Storing timber under oxygen exclusion
can preserve timber quality. However, the method is not applicable for
conserving large amounts of timber due to the requirements and restrictions
described above. It should therefore be limited to short-term conservation of
high quality (hardwood) assortments on sealed surface sites.
The Department for Forest Use of the
Forest Research Institute holds more information and advice on this storage
method. Preparatory training has to be provided for the concerned staff.
safety: When storing green (still damp) timber under oxygen exclusion in foil,
temperatures within the stack rise. Ideal living conditions for mould are the
result. A breathing mask should therefore be worn when opening the stack to
prevent allergic reactions when inhaling the fungus spores.
- Bort, U.; Hörger, R. (1991):
Konservierung von Holz in kontrollierter Atmosphäre. Versuchsbereichte der FVA
Baden-Württemberg, Abt. AWF, Freiburg, S. 1-13
Brammer, T. (2001):
Qualitätsuntersuchungen bei folienkonservierten Furnierbuchen. Versuchsberichte
der FVA Baden-Württemberg, Abt WN, Freiburg, S. 1-25
Gross, M; Mahler, G; Metzler, B.
(1992): Ergebnisse der
Holzlagerung unter Schutzgas. Versuchsberichte der FVA Baden-Württemberg, Abt.
AWF, Freiburg, S. 1-35
Maier, T. (1995):
Alternative Holzkonservierung durch Sauerstoffentzug – Methodik und erste Ergebnisse.
Versuchsberichte der FVA Baden-Württemberg, Abt. AWF, Freiburg, S. 1-28
Maier, T. (1997):
Alternative Holzkonservierung durch Sauerstoffentzug – Lagerungsverlauf und
Holzqualität bei der Auslagerung. Versuchsberichte der FVA Baden-Württemberg,
Abt AWF, Freiburg, S. 1-55
Maier, T.; Schüler, G.; Mahler, G. (1999): Ganzjährig
frisches Rundholz aus dem Lager. In Holz-Zentralblatt Nr. 73 vom 18. Juni 1999.
Seite 1092 bis 1094.
Maier, T.; Schüler, G. (2000):
Abschlußbericht zum Forschungsprojekt "Rundholzkonservierung durch
Schutzgas" Teilprojekt 2. Forstliche Versuchs- und Forschungsanstalt
Baden-Württemberg, 139 Seiten, unveröffentlicht
Schleier, D.; Püschel, A. (2002):
Kann die Folienkonservierung zur biochemischen Borkenkäferbekämpfung eingesetzt
werden? Versuchsberichte der FVA Baden-Württemberg, Abt WN, Freiburg, S. 1-27
Schüler, G. (1998): Alternative Holzkonservierung durch Sauerstoffentzug – Umsetzung in die Praxis.
Versuchsberichte der FVA Baden-Württemberg, Abt. AWF, Freiburg. 1-28
Schüler, G.; Schleier, D.;
Mahler, G.; Maier, T. (2001): Rundholzkonservierung in Folie nach "Lothar".
Holz-Zentralblatt Nr. 21, 127. Jahrgang, Seite 295