1. 樹木の凍裂発生機構の研究(平成5年度第39回凍結及び乾燥研究会研究報告)

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This study was carried outto investigate the mechanism of frost crack formation in living trees of Abies sachalinensis. 1) Changes in width of the frost crack during freezing and thawing were measured using a small log (15cm in diameter and 50cm in length) of A. sachalinensis including a frost crack, which has been naturally produced. The frost crack was closed in the thawed state at room temperature of 20℃. In the freezing process, the frost crack began to re-open upon onset of freezing within the inner part of the log being at about -1℃, followed by marked increase of the width of the opening during the freezing period. Further cooling down of the log from -1℃ to -20℃, however, brought about little increase in the width of the crack. Inversely, in the thawing process the frost crack closed during the thawing in the inner part of the log at about -1℃. 2) Wood specimens including pith were taken from the inner parts of tree trunks of A. sachalinensis and Fraxinus mandshurica var. japonica, and dimensional changes in radius of the specimens during freezing and thawing were measured. The specimens collected from areas in which frost cracks had formed, swelled radially during freezing at about -1℃ and recovered to the initial dimensions during the following thawing. On the other hand, the specimens collected from areas far from frost cracks did not increase in radial dimension during the freezing at about -1℃ even in such cases where the specimens contained the same level of moisture as those of areas including frost cracks. 3) A tree trunk of A. sachalinensis including a frost crack was dissected and observed at freezing state by soft X-ray photography and cryo-scanning electron microscopy. Wetwood was observed in the inner part of the tree trunk. In the wetwood region, many internal cracks such as ring and radial-shakes, in which ice crystals segregated, had formed. In particular, it was noted that some of the ring shakes containing ice crystals developed extensively in the outer layer of the wetwood, and that the inner end of the frost cracks did not reach inwardly beyond the ring shakes. These results show that the opening of the frost crack is closely related to the internal swelling during the freezing at about -1℃, and that the swelling is related to the local ice segregation at the intercellular spaces such as ring and radial- shakes. It was suggested that tangential tension strains were induced in the peripheral parts of the tree trunk by the ice segregation occurring in the inner parts of the trunks, and thereby a radial-longitudinal splitting of frost crack was produced.
低温生物工学会の論文
1993-10-20

1. 樹木の凍裂発生機構の研究(平成5年度第39回凍結及び乾燥研究会研究報告)

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