6 Wood Discoloration

6.4 Protection 133
Fougerousse 1985). Discolorations result from oxidative reactions of accessory
compounds with atmospheric oxygen and phenol oxidases (e.g., Neger 1911;
Oldham and Wilcox 1981), from chemical reactions of wood contents with
metals [iron, zinc: e.g., Bauch (1984)], or from microorganisms, particularly
blue-stain fungi, and in some woods, like Ilomba, from “combined influences”
[bacterial pH-change and subsequent chemical reactions (Bauch 1986; see
Fig. 5.5, Table 6.1)]. The practical processing of wood preservation in the
tropics against discolorations and decay is summarized by Willeitner and
Liese (1992) (also Findlay 1985).
Comprehensive investigations on red streaks producing fungi, their reduction
of wood quality and on suitable storage are described by v. Pechmann
et al. (1967). Since fungal damage is usually only superficial in the first months,
deeper discolorations can be limited to a practically insignificant extent, if
the log does not remain in the forest in the warm season longer than some
months. The wet to moist condition of the wood should rapidly run through either
by suitable forest storage (no ground contact, ventilated, shady), or a high
moisture content should be maintained in the sapwood by an unhurt bark.
Attempts of a “biological wood protection” by antagonism are described in
Chap. 3.8.1.
To prevent enzyme-mediated, non-microbial sapwood discolorations such
as sticker stain in ash or grey stain in oak, logs were treated with fumigants to
kill living parenchyma cells (Amburgey et al. 1996; also Schmidt et al. 1997b;
cf. Chap. 8.1.2.2).
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