Developing a dynamic growth model for maritime pine in Asturias (NW Spain): comparison with nearby regions

Abstract

∙Key message: A dynamic growth model was developed for maritime pine in Asturias. During the evaluation process, a stand volume ratio function proved the best of two alternative methods for estimating merchantable volume. Comparison of the developed model with existing models for nearby regions showed that a single model may suffice for the whole of the NW Iberian Peninsula. ∙Context: Maritime pine is one of the most important tree species in NW Spain. There was no existing dynamic growth model for this species in Asturias. ∙Aims: To develop a dynamic growth model for maritime pine in Asturias, by evaluating two different methods of estimating volume (a disaggregation system and a stand volume ratio function), and to compare the developed model with existing models for Galicia and northern Portugal are the goals of this study. ∙Methods: The dynamic model is based on the state-space approach, in which three state variables characterize the stand at any point in time: dominant height, number of stems per hectare and stand basal area. The transition function for the first variable was developed on the basis of stem analysis data in a previous study, while the corresponding functions for the last two variables were simultaneously fitted with data obtained from successive measurements of permanent plots. An appendix outlining the implementation of a stand growth simulator in the R environment is included to facilitate model use and evaluation. ∙Results: When the whole model was used to project the stand conditions, the stand volume ratio function performed best, yielding a root mean square error of 22.4 m3 ha−1 and a critical error of 18.4 %. Comparison with models developed for other regions revealed both similarities and differences, some of which may be attributed to an unequal distribution of the available data in age and site quality classes. ∙Conclusion: The proposed dynamic growth model provided accurate results, and comparison with other region-specific models showed that a single dynamic model may suffice for the whole of the NW Iberian Peninsula.