Site index curves for young Populus tremula stands on Athos Peninsula (northern Greece)

Difference equations derived on the basis of the McDill-Amateis differential functions and from the integral form of the Bertalanffy, Richards, and Korf growth functions were used to model the dominant height growth of young European aspen (Populus tremula L.) stands on Athos Peninsula (northern Greece). Data from stem analysis were used for fitting. Both numerical and graphical analyses were used to compare alternative models. The cross-validation approach was used to analyze the predictive ability of the models. The algebraic difference form of the differential function proposed by McDill and Amateis resulted in the best compromise between biological and statistical aspects and produced the most adequate site index curves. Therefore, it is recommended for height growth prediction and site classification of European aspen stands on Athos Peninsula. This equation is base-age invariant, so any number of points (A1, H1) on a specific site curve can be used to make predictions for a given age A2 and the predicted height H2 will always be the same.