Variation of natural durability of Japanese cedar (Cryptomeria japonica D. Don) (also known as Sugi) was investigated by accelerated tests for decay (Fomitopsis palustris (Berk. et Curt.) Murr.) and termite (Reticulitermes speratus Kolbe) attacks on 13 clones of Sugi trees from Kyushu-Okinawa Region (Fukuka, Ooita, Saga, Miyazaki, Kagoshima). For this purpose, 57 twenty-five years old Sugi trees of various land races were collected from a clonal trial in Kyushu, Ehime Prefecture, Japan. The deterioration by fungal decay and termite attack was determined as the percentage of mass loss of Sugi heartwood. It was mainly observed that the trial clones were individually stronger on fungal decay than termite attack, and the mass losses in either case appeared to vary between the clones. The ranges of mass loss values caused by termite attack were very close to each other within each clone with the lower standard deviation, whereas the actual values of mass loss after fungal decay created large range between each other in most of the clones with the higher standard deviation. Examination of the results reveals that the northern clones from Kyushu-Okinawa Region are more resistant.

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