Age-related equations for above- and below-ground biomass of a Eucalyptus hybrid in Congo

A complete set of equations for below- and above-ground biomass of a natural Eucalyptus hybrid in Congo was constructed. Heteroscedasticity of data was taken into account by fitting weighted non-linear regressions using maximum likelihood estimates. Stand age was introduced as a complementary variable in the equations for a majority of above-ground compartments and led to improved estimates of biomass. Because of the limited number of sampled trees for below-ground parts, it was not possible to develop the same kind of equations. Simple allometric relationships were then fitted for these components (stumps, large, medium, and fine roots). Additivity was verified and showed no significant deviation except for the youngest stand, where the sum of below- and above-ground biomass equations was preferable to the sum of component equations or to the total biomass equation. This set of equations will now be used to evaluate both the mean and the interval of confidence of biomass content and partitioning within the stands.