Abstract: The effect of three different treatments on wood permeability and its mechanism were studied in the paper by air drying and ethanol exchange drying for green wood and by soaking in water then followed by ethanol exchange drying for air dried wood of yezo spruce (Picea jezoensis Var.komarovii) and fir (Abies nephrolep). The results showed that the specimen of green yezo spruce sapwood, heartwood and fir heartwood after air drying had a low permeability of 0.114, 0.045 and 0.111 darcy, respectively. The permeability of green yezo spruce sapwood, heartwood and fir heartwood after ethanol exchange drying was approximately 11.713, 0.074 and 0.144 darcy, respectively. Compared with the permeability of air dried specimen group, the average permeability was increased about 101.5 times, 62% and 30%, respectively. The t test showed that the difference for yezo spruce green sapwood was very significant while for yezo spruce and fir green heartwood it was not significant. The average permeability of yezo spruce sapwood and heartwood and fir heartwood samples which have been air dried for 18 months after the treatment of soaking in water for 2 weeks followed by ethanol exchange drying was increased approximately by 85%, 49%, 65.5% over their controls before the treatment, respectively. The permeability difference of soaking treatment samples versus their controls was significant at the 5% level by t test of paired comparative test. For yezo spruce green sapwood the significant increase of permeability after ethanol exchange drying compared with air drying was mainly due to the lower fraction of pit aspiration, and then the extraction of a small part of extractives from specimens were also probably responsible. For yezo spruce and fir green heartwood the increase of permeability after ethanol exchange drying compared with air drying was not significant because the ethanol exchange drying failed to prevent or decrease pits aspiration in yezo spruce and fir heartwood. For yezo spruce and fir air dried wood the increase of permeability as a result of soaking treatment was probably due to two aspects, that is, the deaspiration of some aspirated pits and the decrease of extractives in the specimen. However, for yezo spruce sapwood the former was probably the primary factor, whereas for yezo spruce and fir heartwood the latter was probably the major reason.

Key words: Wood permeability, Bordered pit, Pit aspiration, Pit deaspiration, Air drying, Solvent-exchange drying, Soaking treatment