The vertical foliage distributions of six understory tree species in a Chamaecyparis obtusa Endl. forest

Summary The relationships between the amounts of foliage and heights of trees were studied for the dominant understory tree species, including three evergreen and three deciduous species, in a secondary forest of Chamaecyparis obtusa Endl. The relationships showed two phases: leaf increasing and stationary phases. In the leaf-increasing phase, the height growth allowed these species to expand the canopy by increasing the number of leaves. In the stationary phase, the number of leaves was relatively constant number irrespective of tree height from 160 to 400 cm. The number of leaves in the stationary phase represents the maximum number of leaves that can be supported by trees under shady conditions. From the analyses of vertical distributions of leaves in six species, mono- and multi-layer foliage distributions were detected. Two evergreen species, Eurya japonica and Cleyera japonica, showed multi-layer foliage distributions, whereas three deciduous species, Lyonia ovalifolia, Rhododendron reticulatum and Vaccinium hirtum, and one evergreen species, Pieris japonica, showed mono-layer foliage distributions. The relationships between the weights of non-photosynthetic and photosynthetic organs of the six species were examined. The proportion of non-photosynthetic organs increased with tree height. The understory species attained the stationary phase and were maintained by minimizing their investment in non-photosynthetic organs, i.e. their height growth was arrested by the shady conditions under the crown trees.