The log yard: what storage does to wood

Logs rarely go straight to the saw. In the yard they wait, and waiting changes them. The articles' storage guidance comes mainly from Bavaria and Switzerland (Europe) and is mostly about spruce, pine and beech.

The biology in one rule

Wood-damaging organisms need oxygen and water. Bavarian guidance (LWF leaflet, 2025) puts the zone of danger at moisture contents from about 20-30% up to about 120%. Above roughly 120% there is too little oxygen; below 30% there is no free water. The strategy follows directly: keep the wood wet, or dry it quickly below 30%, ideally below 20%.

Dry storage

• In-bark dry storage works only for a few weeks, and for winter-felled wood.
• Spruce must leave the yard before the bark beetle flight (March or April, depending on weather), or be stored at least 500 m from conifer forest.
• Piles should be on shaded, wind-sheltered sites, on supports, secured against rolling, at most 4 m high.
• Debarked logs can be dry-stored longer (1 to 3 years for debarked spruce according to the leaflet) but need a ventilated, dry, warm, unshaded site. Debarking cost about 8.50 euro per solid cubic metre for long wood in Bavaria in 2025.
• Logs debarked before storage are not attacked by bark beetles, horntails or longhorn beetles.

Wet storage and sprinkling

Sprinkling keeps logs wet. Figures from the Bavarian sources (Europe):

• water demand about 0.7 litres per second per 1,000 solid cubic metres in interval operation (2025 leaflet)
• minimum economic size about 1 ha per 15,000 m³
• storage times of 3 to 6 years for spruce, at least 2 for pine, and only months for beech
• total cost 18-20 euro per solid cubic metre per year (2025)
• a water-law permit is required

Sprinkling start and stop temperatures and pile height are not given in the articles; take them from the local permit.

Worked example. A sprinkling site holds 15,000 m³. Water demand is 0.7 l/s x 15 = 10.5 l/s while running. Yearly cost at 18-20 euro per m³ is 15,000 x 18 = 270,000 up to 15,000 x 20 = 300,000 euro.

Wet storage has a use-by date

After storm Lothar (1999), the only fungus able to attack properly sprinkled wood was honey fungus (Hallimasch). Observations after earlier storms showed first decay sporadically after the third year in Germany and after about 3 years in Switzerland; a 25,000 m³ spruce pile in Vaud was dissolved just under 3 years after the storm; the worst case began after 2 years. The fungus attacks almost only sapwood, so small logs lose most value. Record the sprinkling start date and plan outflow inside the window.

Hidden changes inside the wood

• Several months of storage can damage pit membranes and greatly raise liquid uptake, which shows up later at coating as dark spots (Holzforschung Austria, 2021).
• Blue stain does not reduce strength but rules out visual-grade use. Early brown or white rot does reduce strength.
• Technical drying kills insects when the core stays above 55 degrees Celsius for several hours.

The bark beetle crisis 2018-2024 (Europe)

Germany's damaged timber harvest (federal statistics, Thünen Working Paper 244) was 31.9, 46.2, 60.1, 50.5 and 44.7 million solid cubic metres for 2018 to 2022, totalling about 233 million. In the Czech Republic trade press reported damaged wood at 30.9 million m³ in 2019 (99% of harvest). Prices for spruce sawlogs first fell under oversupply, then rose as quality fell and fresh logs became scarce (a commercial blog; indicative only). Practical lessons for the mill: sort salvage logs by age and condition on arrival, separate fresh attack from old galleries, debark early, and write explicit blue stain, rot and gallery limits for salvage lots.

Checklist: yard rules for a buyer

• Ask for felling dates; plan summer-felled spruce in weeks unless it is sprinkled or debarked.
• Record sprinkling start dates and plan outflow within about 2-3 years where honey fungus was seen.
• Keep salvage lots separate in receiving and in the contract.
• Test permeability of long-stored wood before coating.
• Keep lot numbers so that felling date and storage start travel with the wood.

Key points

• Damage needs oxygen and water: keep logs wet (above about 120%) or dry them below 30%.
• In-bark dry storage lasts weeks, and spruce must be gone before the beetle flight.
• Sprinkling is costly (18-20 euro per m³ per year in Bavaria, 2025) and has a limited useful life because of honey fungus.
• Blue stain affects appearance grade, not strength; rot does affect strength.
• Salvage lots need their own receiving rules and contract limits.