T he value influences germination of spores, mycelial growth, enzyme ac-tivity (wood degradation), and fruit body formation. The optimum for wood fungi is often in slightly acid environment of pH 5-6 and for wood bacteria at pH 7. Basidiomycetes have an optimum range of pH 4-6 and a total span of about 2.5-9 (Thornqvist et al. 1987). Ascomycetes, particularly soft-rot fungi, may tolerate more alkaline substrates to about pH 11. Thus, the pH values from 3.3 -6.4 in the wood capillary water of living trees and in aqueous extracts of wood and bark samples from trees of the temperate zones and from trading timbers (Sandermann and Rothkamm 1959; Rayner and Boddy 1988; Fengel and Wegener 1989; Landi and Staccioli 1992; Roffael et al. 1992a, 1992b) cor-respond with the pH demands of wood fungi. Over the tree cross section, pH differences can occur, that is for example the heartwood of oaks and Douglas fir is more acid than the sapwood. Furthermore, an initial pH va
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