Abstract
In this study, the effects upon medium and small-sized tree individuals after the dieback of red pine were investigated in Saijo Basin, Hiroshima, in terms of forest structure, tree-ring chronologies, energy balance, vessel parameters of stem cross sections, and the biomass of dead pines. It was found from forest structure that the canopy layer has been greatly reduced due to the withering of red pines, and the highest class has shifted down to medium-sized trees such as Cryptomeria japonica, Quercus serrata, Acanthopanax sciadophylloides, and Ilex rotunda. Also, it was found from tree-ring chronologies that such medium-sized individuals were increasing their thickening growth. This coincides with the fact that downward short-wave radiation can now reach the middle layers so that they are guaranteed the radiation necessary for phtosynthesis, and the percentage of vessel area has risen to support the increasing growth. Such changes began in the second half of the 1970s. However, understory individuals such as Eurya japonica, Lyonia ovalifolia, and Ilex crenata have been left lightly stressed. Also, the dead biomass of red pines was estimated to be 2,204 to 10,870 t/km2. The dieback accelerated the growth of medium-sized trees but it did not encourage the growth of small-sized trees near the forest floor. Consequently, the two layers, which had remained together in the forest before the dieback, have increased the distances between them.
