Biomass functions applicable to oak trees grown in Central-European forestry

This study describes the parameterization of biomass functions applicable to oak (Quercus robur, Quercus petraea) trees grown in the conditions of Central-European forestry. It is based on destructive measurements of 51 grown trees sampled from 6 sites in different regions of the Czech Republic important for oak forest management. The samples covered trees of breast height diameter (D) ranging from 6 to 59 cm, tree height (H) from 6 to 32 m and age between 12 and 152 years. The parameterization was performed for total aboveground biomass and its individual components. The two basic levels of biomass functions utilized D either as a single independent variable or in combination with H. The functions of the third level represented the best function for each biomass component with the optimal combination of available independent variables, which included D, H, crown length (CL), crown width (CW), crown ratio (CR = CL/H), tree age and site altitude. D was found to be a particularly strong predictor for total tree aboveground biomass. H was found to always improve the fit, particularly for the individual components of aboveground biomass. The contribution of CW was minor, but significant for all biomass components, whereas CL and CR were found useful for the components of stem and living branches, respectively. Finally, the remaining variables tree age and altitude were each justified only for one component function, namely living branch biomass and stem bark, respectively. The study also compares the fitted functions with other available references applicable to oak trees.