and ABE, Kazutoki: Effects of thinning in Cryptomeria japonica D. Don stand on its root growth and function of preventing shallow landslide Abstract: Root distribution was investigated targeting eleven Cryptomeria japonica D. Don in thinning stands and non-thinning stands. Whole root systems of the each investigated trees were dug up carefully in the field. And root diameter and length of all roots at every 10 cm interval to depth direction and at 50 cm interval to radius direction. As a result, the whole root volume of the one tree has a good correlation with its trunk volume index and tree number density, respectively. And the amount of roots growing in the sliding surface of the landslide bottom and sides were not increased with increasing stand age. This means that the leading idea so far that the forest function of preventing shallow seated landslide is caused by roots growing on the sliding surfaces might not be correct. We assumed that the forest function of preventing landslide could be generate by suppressing deformation and cracks of the surface soil layer by the large amount of roots growing in it. The root volume in surface soil layer was calculated by the data of Cryptomeria japonica D. Don root distribution. We found that the root volume of surface soil layer in a thinning stands was much more than non-thinning stands from 10 to 30 year old. It is consistent with the relationship between number of the shallow landslides that occurred in younger forests and the stand age.

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