Foliage-canopy structure and height distribution of woody species in climax forests

The correlation between foliage-canopy structure and vertical woody species distribution was examined in seven climax forests ranging from alpine tree limit to tropical rain forest. Foliage density was measured by two-dimensional canopy tomography using photographs. Both foliage density and the vertical species density (the number of woody species having a maximum height within a vertical 1 m) were high in the upper canopy of warm-temperate and subtropical forests, but they were high at lower stratums in the tropical rain forest. Two variables correlated significantly despite the differences in foliage-canopy structures. In contrast to evergreen broad-leaved forests, a clear correlation could not be detected in northern cool-temperate and sub-alpine forests. A possible reason for species convergence in the foliage dense stratum is that species with maximum height in that stratum may be able to survive in the stratum due to symmetrical crown-to-crown interaction. If the maximum height of dwarf species is less than the foliage dense stratum, it may be difficult to survive in the community. The lack of correlation in northern forests may be due to poor canopy tree flora and a mixture of different life forms (non-sprouting trees and sprouting shrubs).