Comparative analysis of balsam fir wetwood, heartwood, and sapwood properties

Physical, anatomical, chemical, and microbiological properties of wetwood in heartwood were compared with those of sapwood and normal heartwood in balsam fir (Abies balsamea (L.) Mill.). Wetwood found only in heartwood of balsam fir had significantly higher moisture content (MC) than normal heartwood but not significantly higher MC than sapwood. No differences in relative density or shrinkage properties were found among tissue types. Wetwood tissue needed longer times to dry to an equilibrium MC of 15%, not only because of its high initial MC, but also because of its lower moisture permeability (diffusion coefficient) in this particular MC range (from initial MC to 15% equilibrium MC). However, there were no significant differences in drying rates for the different tissues when drying from 15% MC to 8% MC. Anatomically, wetwood is similar to normal heartwood, and it has no distinctive characteristics except a greater frequency of bacteria. Energy dispersive X-ray analysis showed that all of the tissues contained the same inorganic elements. Both high-performance liquid chromatography and ash analysis showed that wetwood is chemically closer to normal heartwood than to sapwood. Wetwood was significantly more acidic than either normal heartwood or sapwood. A large number of bacterial genera were found in all three tissues, but there were no consistent or significant differences in bacterial presence or activity among tissue types.