Tropical tree height and crown allometries for the Barro Colorado Nature Monument, Panama: a comparison of alternative hierarchical models incorporating interspecific variation in relation to life history traits

Abstract

Abstract. Tree allometric relationships are widely employed for estimating forest biomass\nand production and are basic building blocks of dynamic vegetation models.\nIn tropical forests, allometric relationships are often modeled by fitting\nscale-invariant power functions to pooled data from multiple species, an\napproach that fails to capture changes in scaling during ontogeny and\nphysical limits to maximum tree size and that ignores interspecific\ndifferences in allometry. Here, we analyzed allometric relationships of tree\nheight\xa0(9884 individuals) and crown area\xa0(2425) with trunk diameter for 162\nspecies from the Barro Colorado Nature Monument, Panama. We fit\nnonlinear, hierarchical models informed by species traits –\nwood density, mean sapling growth, or sapling mortality – and assessed the\nperformance of three alternative functional forms: the scale-invariant power\nfunction and the saturating Weibull and generalized Michaelis–Menten (gMM)\nfunctions. The relationship of tree height with trunk diameter was best fit\nby a saturating gMM model in which variation in allometric parameters was\nrelated to interspecific differences in sapling growth rates, a measure of\nregeneration light demand. Light-demanding species attained taller heights at\ncomparatively smaller diameters as juveniles and had shorter asymptotic\nheights at larger diameters as adults. The relationship of crown area with\ntrunk diameter was best fit by a power function model incorporating a weak\npositive relationship between crown area and species-specific wood density.\nThe use of saturating functional forms and the incorporation of functional\ntraits in tree allometric models is a promising approach for improving estimates\nof forest biomass and productivity. Our results provide an improved basis for\nparameterizing tropical plant functional types in vegetation models.