During tree growth, mechanical stresses accumulate in the stem because of the increasing tree weight and wood maturation. These "growth stresses" fulfil essential biomechanical functions: they allow the control of the tree orientation and improve its resistance against bending loads. But they generate technological problems during tree transformation, causing heart checks after cross-cutting, checks and deformations of boards after sawing, etc... Research in this area aims at understanding how these stresses appear during growth, in order to find solutions to reduce them. Radial profiles of growth stress were studied by measuring the longitudinal strains due to the release of growth stress at different radial positions on diametrical boards. A biomechanical model based on the beam theory adapted to growing structures is presented. It allows calculating growth stress accumulation in a cross-section of any shape, with any distribution of material properties. Experimental profiles were compared to those simulated by the model assuming particular growth scenarios. They were consistent with the predictions of biomechanical models, showing a maximal tension at the periphery of the tree, and an increasing compression towards the tree centre. Asymmetric profiles were sometimes observed, and were consistent with simulations obtained when eccentric diameter growth and asymmetric maturation strains were taken into account. The correspondence between experimental results and simulations provides a first validation of the biomechanical model of growth stress accumulation in stems.