6 Wood Discoloration

3.3 Wood Moisture Content 65
of brown-rot decayed wood was more than that of undecayed samples at low
relative humidities, but at higher humidities (about 37%) the situation was
reversed. Absorptiveness also increased after pretreatment with blue-stain
fungi (Fjutowski 2005).
– moisture uptake, which can occur by five ways: rainfall, absorption from air,
capillary penetration of water into wood in ground contact or in buildings
by condensation on wood surfaces, water transport by the mycelium, and
water formation by fungal metabolism,
– loss of water: in wood with large pores by the force of gravity, furthermore
by evaporation as a function of temperature, humidity, and matrix potential
as well as by water transport via mycelium.
The cardinal points of the wood moisture content for some decay fungi are
shown in Table 3.6, whereby the data vary, however, depending on the fungal
isolate, the wood species, and the testing method. Laboratory findings and
practice observations may also yield different results (Ammer 1964; Savory
1964; Cockcroft 1981; Thörnqvist et al. 1987; Viitanen and Ritschkoff 1991a;
Huckfeldt et al. 2005).
Generally, it applies to wood fungi: The minimum for wood decay is near
the fiber saturation point of about 30% u, however, commonly slightly above
this range because only then there is free water in the lumen void space. Some
house-rot fungi, however, could colonize wood in laboratory culture, whose
moisture was significantly below fiber saturation (minimum 18% u) before
the mycelium contacts the woody substrate, because these fungi transported
water from a moisture source by means of mycelium. The minimum for decay
of pine wood samples by these house-rot fungi was between 22 and 37% u
(Huckfeldt and Schmidt 2005; cf. Table 8.7). The optimum differs depending
on the fungal species and affects the occurrence of different fungi in differently
moist biotopes: For example, the optimum is at 50–100% for tree-inhabiting
blue-stain fungi and below 50% for lumber blue-stain fungi (Bavendamm
Table 3.6. Cardinal points of wood moisture content (% u) for some wood-decay fungi
(literature data)
Minimum Optimum Maximum
Antrodia spp. 30 35–55 60–90
Coniophora puteana 26–30 30–70 60–80
Daedalea quercina 40
Gloeophyllum spp. 30 40–60 80–210
Heterobasidion annosum 45
Lentinus lepideus 35–60
Phlebiopsis gigantea 100–130
Serpula lacrymans 26 30–60 55–225
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