Seasonal courses of leaf CO 2 gas exchange in a growing season were examined in saplings of Thujopsis dolabrata'var, hondai and Quercus mongolica var. grosseserrata in a cool temperate deciduous forest. Between the two tree species there were no large differences in the light compensation point of leaf photosynthesis, except for the season of new leaf expansion. However, light-saturated rates of net photosynthesis were obviously high in T. dolabrata var. hondai. Evergreen T. dolabrata var. hondai saplings had large photosynthetic production in two seasons, before the emergence of new foliage and after foliage fall of the overstory deciduous trees, because of the significantly high solar radiant energy penetrating under the forest canopy during the seasons. Saplings of deciduous (2. mongolica var. grosseserrata were heavily shaded throughout the growing season by foliage of the overstory trees, which resulted in a low daily surplus production. The annual surplus production of leaves in the growing season was estimated to be 2300 mmol CO 2 m -2 in T. dolabrata var. hondai and -100 mmol CO 2 m -2, slightly negative, in Q. mongolica var. grosseserrata. These results supported the high survivability of T. dolabrata var. hondai saplings and the high mortality of Q. mongolica var. grosseserrata in the deciduous forest.

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237 We investigated the mean crown lengths of Japanese cedar trees in overcrowded mature plantations. In pooling the data for unthinned young and overcrowded mature plantations, the mean crown length of Japanese cedar trees in each plantation was positively correlated with mean upper tree height in each plantation. However, the average mean crown length of trees in overcrowded mature plantations was m, which was only slightly greater than that of trees in unthinned young plantations m . Thus, if intensive thinning is not conducted, the crown lengths of mature trees will not steadily increase.

greater the DBH, the more vigorous the growth of the trees with a crown length of over 4.0 m.

Seedlings of the three coniferous species including Thujopsis dolabrata var. hondai Makino were raised under weak shade in a nursery in order to examine the photochemical and nonphotochemical dissipations of excited energy at PSII. The dry matter growth 20 weeks after germination was smallest in T. dolabrata var. hondai. This was due to the low photosynthetic capacity in addition to the small leaf weight ratio of the seedlings and the large leaf specific weight. The specific ranking of rETRmax (the maximum relative electron transport rate) was different from that of NPQmax (the maximum of non-photochemical quenching); T. dolabrata var. hondai was characterized by the high NPQmax relative to the low rETRmax. A slight depression in FJF, (light stress parameter) was recognized only for Cryptomeria japonica in the cotyledon period. A large depression in Fv/Fm was observed for C. japonica and T. dolabrata var. hondai in the postcotyledon period. These depressions in Fv/Fm seemed to be closely associated with the low levels of rETRmax but may have also been related to the effects of NPQmax and foliage morphology and architecture. The light responsibility of T. dolabrata var. hondai seedlings differed greatly from that of Pinus densif lora Sieb. et Zucc. and differed significantly from that of C. japonica.

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