Site index model for Pinus sylvestris in north-east Spain

The McDill–Amateis difference model and difference forms of the Chapman–Richards, Hossfeld, Lundqvist–Korf and Schumacher growth models were derived to model the dominant height growth of Scots pine (Pinus sylvestris L.) in north-east Spain. Data from permanent sample plots and stem analysis were combined and used for modelling. Both qualitative and quantitative criteria were used to compare alternative models. The PRESS (prediction sum of squares) statistic was used to analyse the predictive ability of the models. The polymorphic difference equation derived from the Hossfeld function resulted in the best compromise between biological and statistical aspects, producing the most adequate site index curves. This dynamic equation can compute predictions directly from any age-dominant height pair without compromising consistency of the predictions. The predictions of dynamic equations are unaffected by arbitrary changes in base-age. The presented Hossfeld equation is recommended for site classification and dominant height prediction in Scots pine stands in north-east Spain.