The variations of the modulus of toughness and wind resistance of seedling- and vegetatively-propagated Japanese cedar (Cryptomeria japonica D. Don) grown in central Taiwan and receiving various intensities of thinnings were investigated. A typhoon in 1986 caused serious damage to trees in Taiwan and surveys indicated that vegetatively-propagated Japanese cedar trees received twice as much wind damage as those of seedling-origin. At the base of a tree investigated, the modulus of toughness decreased markedly outward from the pith, but at other higher locations, such a tendency was uncertain. Moreover, the magnitude of the modulus of toughness at the base was much larger than that obtained from other heights. The values of toughness were significantly greater for seed-originated trees than those of vegetatively propagated trees. Significant effects of thinning intensities on the toughness of Japanese cedar were not observed.
