BELOWGROUND AND ABOVEGROUND ALLOMETRIES OF SHADE-TOLERANT SEEDLINGS IN A JAPANESE WARM TEMPERATE RAIN-FOREST

1. A comparative study has been made of the allometric relationships among below-ground and above-ground dimensions of seedlings (6.5-27 cm tall) of 14 abundant shade-tolerant species taken from the forest floor in a warm-temperate rain forest on Yakushima Island, southern Japan. 2. The allometric lines between below-ground dimensions are significantly different between species, which reflects the differentiation between the species developing tap-roots and those developing horizontal fine roots in the same forest. The difference correlates with a difference in seed size, but not with height at maturity or habitat (ridge vs slope or gully). It is hypothesized that the differences in root architecture are related to 'choices' in microsite for establishment, the large-seeded tap-rooted species being better suited to soft soil and deep litter, and the small-seeded lateral rooters to rocky soil and a lack of litter. 3. The allometric relationship relating below- and above-ground dry mass is not sufficient to characterize a species' architecture; a species may have a large ratio of root mass to shoot mass but a low ratio of fine-root length to leaf area. 4. Interspecific differentiation in below-ground allometries at the seedling stage is not correlated with that in above-ground allometries at the seedling stage or with that in above-ground allometries at the sapling stage with developed branching architecture. Allometric 'design' in architecture at the sapling stage (related to earlier or later canopy-gap formation) is variously combined with that at the seedling stage (related to the microsite of establishment).