Effect of tree, stand, and site variables on the allometry of Eucalyptus globulus tree biomass

The objective of this study was to develop a system of compatible equations to estimate eucalyptus ( Eucalyptus globulus Labill.) tree aboveground biomass and biomass of tree components for forest biomass prediction across regional boundaries. Data came from 441 trees sampled on several sites (99 and 14 plots in planted and coppice regenerated stands, respectively) representative of the eucalyptus expansion area in Portugal. The system of equations, simultaneously fitted using seemingly unrelated regression, was based on the allometric model for the biomass of stem wood, stem bark, leaves, and branches. Total aboveground biomass was expressed as the sum of the biomass of the respective tree components. The study allowed the following conclusions: (i) there is a significant increase in the predictive ability of the models that include height (stem components) or crown length (crown components) as an additional predictor to diameter at 1.30 m; (ii) there is a clear effect of the stage of development of the stand on tree allometry, with a decreasing pattern of the allometric constants; (iii) no effect of stand density, site index or climate on tree allometry was found; and (iv) for practical purposes, the same system of equations can be used for planted and coppice regenerated stands.