Base-age invariant models for predicting individual tree accumulated annual resin yield using two tapping methods in maritime pine (Pinus pinaster Ait.) forests in north-western Spain

Abstract

In southern Europe, especially in Spain and Portugal, maritime pine resin is one of the main non-timber forest products. After suffering a crisis at the end of the 20th century, it is currently a growing sector. In Spain, depending on the area, the management of pine forests is one of the pillars of the national bioeconomy. In addition to timber production, these forests may be oriented towards resin production only, or resin production as a complementary activity to timber production. In both cases, as in any sector, it is essential to have tools to manage and anticipate production, especially in the new context of the bioeconomy. For this reason, the aim of this study is to develop a dynamic model to estimate the accumulated resin yield during the resin production season. For this study, 180 trees from three plots located in the northwest of the Iberian Peninsula were resin tapped using two extraction methods (non-mechanized and mechanized circular notching) and stimulant pastes. Four base models were used from which eight equations were derived using ADA and GADA techniques. The most efficient equations, both for modelling with the train data and for prediction with the test data, were those derived from the Bertalanffy-Richards model. The RRMSE was 23% for the non-mechanised method and 29% for the mechanised circular method. The results of this study make it possible to add the cumulative annual resin yield of maritime pine to the processes that the Bertalanffy-Richards equation is capable of modelling. Furthermore, the great versatility of these models will be of great use to the forest manager in optimising the annual harvesting season as well as for the scientific community.