Vertical distribution of trunk and crown volume in tropical trees

Tree volume equations including branches are scarce in forestry literature, especially in diverse tropical forests, where the variability in tree shapes hampers the development of overall volume descriptions. We present species-composite cumulative volume profile models that describe the volume contained up to a given height in the trunks and crowns of tropical trees. We use terrestrial laser scanning (TLS) and quantitative structure models to estimate the trunk and crown volume of 177 trees (49 species) in a lowland tropical forest in the Barro Colorado Island in Panamá. These models were fitted using multilevel mixed-effects models recognizing the diversity of architectures in tropical trees. We found that (1) the rate at which volume accumulated with height was much higher and variable in the whole tree (trunk + branches) than only in the trunk; (2) the variability in the rate of volume accumulation was three times higher in the trunk and nine times higher in the whole tree across individuals within species than between species; and (3) parameters describing the rate of volume accumulation significantly depended on the height of attachment of the lowest branch, but not on the tree size. The resulting equations can be used to estimate the proportion of volume contained up to any height in tropical trees.