Characteristics of the Light Response in Seedlings and Saplings of Two Mid-Successional Species, Ash and Kalopanax, During the Early Stage of Regeneration in a Mature Forest

Abstract

Growth characteristics of ash (Fraxinus mandshuricavar. japonicd)and kalopanax (Kalopanax pictus), two mid-succcs-sional species, were monitored in relation to seasonal light in a deciduous broadleaf forest. During the growing, relative light intensity of the gap was 4 to 6 times higher than that under the closed canopy. Seedlings could be found on the mixed hardwood forest floor where relative light intensity was around greater than 7% of full sunlight. When saplings gap openings which had relative light intensities above 20%, they quickly developed lateral branches and increased their foliage volume. The light-photosynthesis curve of seedlings of both species showed a curve typical of the “shade leaf” type even though they grew under sunlight. In contrast, saplings of both species showed the “sun leaf” type of light-photosynthesis curve. This seedling to sapling shift from shade to sun adaptation was also found in other foliage characteristics. This study shows that species can efficiently adjust their leaf and branch characteristics to changing light environments from shade to openings in a forest.