Studies on morphology and occupancy area of trees provide knowledge on features and functions of forest ecosystem, especially in terms of competition and growth of trees. The main purpose of this work was to develop models for shape and size relationships of Araucaria angustifolia in natural forest remains of species. Dendrometric and morphometric variables from 210 trees from three sites were used. Results showed that the species present different shape and size, vigor and productive capacity in evaluated sites. Fitted models indicated that there was transition in competition mode (symmetric or asymmetric) for resources, which is result of available growing space for trees. Relationship between shape and size is derived from slope of regression line and regarded as an indication of need for silvicultural interventions to reduce competition, which is a key information for obtaining better practices in forest management.