To metabolize wood, decay fungi require a high MC, usually above the fiber saturation point
, but they also generate a significant amount of water as a result of the wood degradation process by this known reaction:
Wood can store water in its pore structure beyond the fiber saturation point
but it does not get any bigger.
When the moisture content of the tracheids drops below the fiber saturation point
(FSP), that is when lumina contain no "free" water but cell walls are fully saturated with liquid, further dehydration leads to cell wall shrinkage processes.
More precisely, wood only changes dimension between an absolutely dry state (completely free of moisture) and its fiber saturation point
(the point at which the cell walls of the wood fibers are completely saturated with moisture).
Fiber saturation point
, tangential shrinkage, cell structure, and a host of other technical terms have meaning and purpose in the ensuing process for each individual species.
The finding of diffusion occurring at 18 to 20 percent moisture content conflicts with the assumption that diffusion will cease at moisture contents below the fiber saturation point
Drying checks develop because the fiber saturation point
is reached far earlier in the shell than in the core of a specimen and because wood is an anisotropic material concerning shrinkage (radial = in direction of the annual rings: tangential = 1 : 1.
In both cases, however, the materials were at or above the approximate fiber saturation point
2001) suppose that in radiata pine (Pinus radiata) sapwood within-ring internal checking is caused by water tension and not by differential shrinkage, because checking occurred before the fiber saturation point
Because of the limitations of the resistance-type moisture meter, only MC values below the fiber saturation point
can be obtained accurately.
In general, wood dried to below the fiber saturation point
tends to shrink as the water bound to the cellulose microfibrils is removed (Panshin and de Zeeuw 1970).
The influence of moisture content up to 23 percent, which is below the typical fiber saturation point
of wood, on the transverse thermal conductivity is presented as well.