In this paper, a model on intraspecific competition is presented. The model is based on the concepts of areas of influence and interference. The basic hypothesis assumes that the optimisation between space occupation (maximum) and competence (minimum) is a consequence of interactions among individuals. Individual size of trees (DBH, canopy diameter) as well as size and distance to the neighbours are taken into account as relevant parameters. The model has been applied to three forest stands (Pinus nigra, Pinus halepensis and Pseudotsuga menziesii) and the results obtained are compared with some simulated stands in order to examine the biological meaning of the stands structure. These simulated stands have been obtained modifying the position of trees but conserving the same density and DBHs distribution. In other simulators, individual trees positions remain unchanged but DBHs are permuted. Results showed that real stand present the optimum relationship between space occupation and competence.