Models of 3D crown structure for Scots pine (Pinus sylvestris) and silver birch (Betula pendula) grown in mixed forest

The interplay between plant structure and functioning determines vital plant characteristics, such as the efficiency of light capture by the foliage, and thus continuous efforts have attempted to include plant architecture in plant growth models. We constructed two crown structure models enabling the generation of 3D trees using simple tree measurements as input for Scots pine ( Pinus sylvestris L.) and silver birch ( Betula pendula Roth.), boreal species growing in mixed stands. The data for the models were obtained from sample-based digitizing of 3D crown architecture accompanied by characterizations of stem, branch, and foliage volumes and biomass. A set of equations was used to predict local crown characteristics on the basis of local predictors and tree-level input variables such as tree height, crown height, diameter at breast height, and the degree of competition. The 3D tree model was realized within the LIGNUM tree modelling framework. Comparison with data showed that the model adequately predicts the distribution of biomass into different crown components as well as the distribution of foliage within the tree crowns. The applicability of the simulations is at its best when examining Scots pine and silver birch trees growing on medium fertile mixed stands in Finland.