Tetsuto Sugai*, Kazuhito Kita***, Toshihiro Watanabe** and Takayoshi Koike*
* Silviculture and Forest Ecological Studies, Hokkaido University, Sapporo 060-8589, Japan
** Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
***Hokkaido Forestry Research Institute, Bibai 079-0198, Japan