Tree Species Stratification in Relation to Allometry and Demography in a Warm-Temperate Rain Forest

Abstract

1 We studied stratification of tree species by analysing the allometry and demography of 14 abundant species in a warm-temperate rain forest on Yakushima Island, southern Japan. 2 We regressed relationships between trunk diameter at breast height (d.b.h.) and top height of trees using an expanded allometry which incorporates an upper limit to height. As trees grew up towards the canopy, individuals with the same d.b.h. were taller if they came from species with larger maximum height. This appeared to reflect a trade-off between height growth and lateral growth of crowns. Two canopy dominants continued to gain in d.b.h. after they had reached the canopy, while their height remained almost constant. 3 We examined size-specific patterns of relative growth rate of d.b.h. from a decade of field censuses. By fitting a Gompertz-type growth curve to size-specific growth of individual trees, we derived a projected potential maximum size for each species. The projected maximum size (both d.b.h. and height) was similar to the observed value for most species. Three canopy species exhibited larger projected maximum d.b.h. than observed values; the difference seemed to be due to mortality during the long period that each of these species resides in the canopy. 4 Understorey species recruited equally well as larger-growing species amongst the 14 studied species, although their tree mass increments per unit time were smaller. This suggests that understorey species have more effective recruiting capacity relative to vegetative growth.