Variation in allometry and tree architecture among Symplocos species in a Japanese warm-temperate forest.

We compared tree architecture and allometry among five Symplocos species (Symplocos myrtacea, Symplocos lancifolia, Symplocos lucida, Symplocos glauca, and Symplocos theophrastiifolia) in a Japanese warm-temperate forest to understand the causes of interspecific variations in these characteristics. S. lancifolia, S. glauca, and S. theophrastiifolia grew at elevations below 500 m, whereas S. lucida grew on ridges irrespective of elevations, and S. myrtacea grew at elevations above 590 m. The species that shared a habitat exhibited trade-offs between height growth and crown area extension that might reflect differentiation in their regeneration niches. S. lancifolia showed the lowest height growth and widest crown extension, whereas S. theophrastiifolia showed the greatest height growth and lowest crown extension. S. glauca was intermediate between these species. S. lucida grows on ridges characterized by strong winds and the absence of other Symplocos species; it had the thickest stem and second-narrowest crown of the five species, possibly due to mechanical stability constraints. S. myrtacea was smallest at the onset of reproduction, and its fruits developed under closed canopies. Its architecture and allometry may increase seed production. Variation in tree architecture and allometry among the five species appear to be related to differentiation among regeneration niches, mechanical stability, and reproduction constraints.