Distance independent tree diameter growth model for cork oak stands

A diameter increment model for cork oak was developed based on measurements taken twice at 72 permanent plots in cork oak forest in southern Spain. Empirical and semi-empirical models were compared. In the empirical model diameter increment was expressed as a function of tree and stand characteristics such as diameter, density and site index. In the semi-empirical model, the diameter increment was expressed as a function of the potential diameter growth multiplied by a modifier, applying a correction factor to the potential growth to take into account the variability associated with different climatic conditions in the years when the plots were measured. The first step was to select the best model for each one of these methods, considering both statistical properties and predictive ability. The two chosen models were then compared through the characterisation of the model error. Both models behaved similarly explained about the same amount of variation in diameter increment and provided realistic diameter increment predictions.