Wood-staining fungi

Wood staining fungi can cause bluish, brownish or other shades of discolouration, often limited to sapwood. As a rule, the fungi settle first in the rays. This is because they can’t actually degrade the substance of the wood and live on carbohydrates and fats which are stored in the sapwood rays. Although they don’t destroy the wood, permanent staining can greatly reduce its value.

What kind of staining occurs frequently?

Stains caused by sapstain fungi and mould are particularly common in coniferous timbers. The sapstain fungi can also grow into the wood so that the stain penetrates deeply. This makes it impossible to plane the stain away mechanically. Mould only discolours wood on the surface through its spores, but often leaves mould stains after their removal. Special anti-sapstain preservatives, that should be applied directly after the timber is cut, provide protection against wood-staining.

Is staining always caused by fungi?

Not all stains are caused by microorganisms. Dirt and dust particles on the wood’s surface can be mistaken for mould. Cut wood can react to iron particles, also resulting in stains. Such stains occur in wood types that contain tanning agents, like oak and sweet chestnut, but also Douglas fir, when they come into contact with iron or water with a high iron content during storage or processing. The phenolic content in the wood reacts with the iron ions and forms dark colourings.
Besides, wood can also suffer discolouration in the living tree, as is the case with red heartwood formation in beech trees.