Regeneration processes and ecophysiological properties of young growths in the floor of natural forests of deciduous tree species and hiba arborvitae

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Light compensation points of young growths of hiba arborvitae were in the range of 4 to 6 umol quanta m^<-2> s^<-1> : they do not have particularly lower compensation points but rather higher values compared with other woody species growing on the same forest floors. Between young growths of hiba arborvitae and mizunara oak there were no large differences in the light compensation point, except for the new leaf expansion season. However, light-saturated rates of net photosynthesis were obviously high in hiba arborvitae. Hiba arborvitae young growths, attaching evergreen leaves, performed active photosynthetic production in two seasons, before new foliage emergence and after foliage fall of the overstory deciduous trees, because of the significantly high solar radiant energy reaching under the forest canopy during the seasons. Seedlings of deciduous mizunara oak were heavily shaded throughout the growing season by foliage of the overstory trees, and it resulted in low daily surplus production. From the repeated census of the young growths it was apparently hard for mizunara oak to survive for more than three or five years after germination. In contrast the young growths of hiba arborvitae did not wither and die and their distribution density was rather increased by so called creeping branch propagation. Such growth and development of the hiba arborvitae young growth population would be provided by the resource availability peculiar to under the forest canopy dominated by deciduous trees.