Branch growth and allocation patterns of saplings of two Abies species under different canopy conditions in a subalpine old-growth forest in central Japan

Abstract

Branch growth and biomass allocation of saplings of two Abies species under three different canopy conditions (evergreen coniferous Abies canopy, deciduous broad-leaved Betula canopy, and canopy gaps) were examined in a subalpine old-growth forest in the northern Yatsugatake Mountains, central Japan. Both A. mariesii and A. veitchii saplings showed similar morphological plasticity: saplings growing in gaps had conical crowns, whereas those under evergreen and deciduous canopies had umbrella-shaped crowns. Both Abies species grew more in stem diameter than in stem height under evergreen and deciduous canopies. Under evergreen and deciduous canopies, A. veitchii saplings invested more biomass in stems and less in leaves and branches than did A. mariesii. The mean longevity of leaves and branches of A. veitchii saplings was shorter than that of A. mariesii saplings under evergreen and deciduous canopies. These results suggest that A. veitchii saplings have an efficient umbrella-shaped crown for light interception and invest relatively little biomass in leaves and branches compared with A. mariesii saplings in shaded conditions. However, branch mortality of A. veitchii saplings may be higher, because the species’ high leaf area ratio and specific leaf area may increase its susceptibility to herbivory and disease and also because the slender branches of A. veitchii saplings would be more likely to break under the weight of snow. The growth strategy of A. mariesii in shade is considered persistent, while that of A. veitchii saplings emphasizes height growth.