Abstract Key message This study provides new equations to estimate crown width and percent crown cover of cork oak ( Quercus suber L.), helping forest managers understand forest structure and making informed decisions on understory management and thinning operations. These equations can either be used as standalone solutions or help adapt existing tools, such as the Physiological Processes Predicting Growth (3PG) model, thereby supporting better decisions to protect Mediterranean woodlands facing environmental changes. Context Tree crown width and canopy cover are key variables that influence forest productivity, regeneration, and ecosystem functioning. In cork oak stands, low regeneration and sparse canopy cover are common challenges. There is no established consensus on the optimal stand density, and research on this topic remains limited. Aims This study aims to develop robust models to estimate tree crown width and canopy cover at the stand level, designed for both standalone application and integration with the outputs of the widely used 3PG model. In addition, the proposed models can be used to evaluate alternative methods for estimating light interception in the 3PG model. Methods The first step involved the development of a crown width model based on stand variables, computed with all trees in the stand, including trees with DBH < 7.5 cm, which is really important in young even-aged stands and in close-to-nature management. This model was then used to calculate missing crown widths, followed by the development of new models to estimate canopy cover based on stand variables and some biomass component(s). Several formulations of allometric and monomolecular functions were tested to produce alternatives both for general use as a decision-support tool and use within the 3PG model. Results The monomolecular function was preferred for its broad applicability across stand ages. Three final formulations, one using basal area and the other two using leaf biomass as the main predictor, showed strong predictive performance (EF pred. = 0.88, 0.91 and 0.91, respectively) and maintained biological relevance. The model based on leaf biomass and tree density enables canopy cover estimation independent of stand age and uses variables directly provided by the 3PG model. Conclusion Improved estimates of crown width and canopy cover allow for more accurate assessments of the relationship between the tree canopy and the understory vegetation, which enables the use of canopy cover as thinning criteria. Therefore, the equations developed in this study are valuable tools for supporting sustainable forest management. Furthermore, one of the canopy cover models was specifically designed for direct integration into the 3PG model, and the set of equations developed open new avenues to test alternative methods for estimating light interception within this framework.
Jorge et al. (Mon,) studied this question.