A combined model, with a matrix component to describe the trees whose diameters are below a threshold, and an individual-based component for the trees above the threshold, is proposed. The combined model is derived from a matrix model and simulates the dynamics of a tropical rainforest in French Guiana, with a management orientation. The methodology to build a combined model starting from a matrix model is specified. The crucial point lies in three continuity conditions at the transition diameter. To establish them, both the matrix and the individual-based components are reformulated into a continuous distribution-based model, which is analytically more tractable. The combined model provides a more detailed description of the tail of the diameter distribution, which can be useful for management purposes. It also permits the separation of the dynamics of small trees, which are numerous and for which matrix coefficients can be quite precisely assessed, from the dynamics of large trees.