Crown Architecture and Life-History Traits of 14 Tree Species in a Warm- Temperate Rain Forest: Significance of Spatial Heterogeneity

Abstract

1 We examined architectural and life-history traits of 14 abundant non-pioneer tree species at various size classes in a warm-temperate rain forest on Yakushima Island, southern Japan. The 14 species were categorized according to maximum attainable size (five canopy, seven subcanopy and two understorey species). 2 Within each maximum-size category, the relative frequency of trees of 2-8 cm d.b.h. (trunk diameter at breast height) in gaps compared with closed-canopy stands differed between species. In the closed-canopy stands, the positions of the crowns in the heterogeneous canopy differed between species within each of the canopy and subcanopy categories at 8-40 cm d.b.h. 3 We regressed the relationship between d.b.h. and crown architecture by a non-linear allometric equation for the 14 species. There was a continuum from wide-crown species to narrow-crown species within canopy and subcanopy categories at 2-16 cm d.b.h. The two understorey species were wide-crown species throughout their ontogeny. 4 Interspecific differences in both rate of increase of d.b.h. and mortality over 10 years (1983-93) were detected within the canopy and subcanopy categories. 5 Principal component analysis based on five architectural and life-history traits revealed species differentiation within the canopy and subcanopy categories, reflecting a trade-off between responsiveness to increasing light in narrow-crown species and shade tolerance in wide-crown species. Multiple regression analyses suggested that most of these traits could be predicted by the light environments experienced by species rather than by species' maximum sizes. We concluded that species differentiation in this community was primarily related to different regeneration behaviour in gaps by trees of 2-8 cm d.b.h., and to different space occupation in the heterogeneous canopy at 8-16 cm d.b.h.