The main wood degradation patterns at advanced stages of
decay can be identified macroscopically and microscopically,
as described above. General changes in the chemical composition
of wood can be also observed after fungal-induced decay
(Table 1). However, a precise analysis of the degradation type
requires chemical analysis of cellulose and lignin contents and
of the modifications in the decayed wood. Lignin in wood is
traditionally estimated by the Klason method, which is based
on total acid hydrolysis of polysaccharides and gravimetric
estimation of the lignin content (after deducing ashes and
protein). This method, however, is time-consuming, and
requires a considerable sample volume. In addition, its application
to samples containing modified lignin (as in rotted
wood samples) is problematic because it has been developed
for lignin in sound (undecayed) wood. Estimation of Klason
lignin is often combined with analysis of wood polysaccharide
composition by gas chromatography (GC) of the monosaccharides
present in the acid hydrolysate.