Capsis is a multi-platform simulation framework, being used by an increasing number of french modellers to build forest dynamics models (see the presentation entitled "CAPSIS: Computer-Aided Projections of Strategies In Silviculture", same workshop). Formerly written in SmaiTalk, Selva, a model dedicated to the study and simulation of tropical rainforest dynamics on a spatialized per tree basis, has been ported on this new framework. This paper address the process initiated by this porting, which lead to a completely new approach. A wide spectrum of requests emerged from interactions with current and future users of the model. In order to satisfy most of them and provide as global solutions as possible, generic mechanisms were prioritized. Depending on their needs and available data, users can configure "à la carte" models to handle an ecological context and then focus their attention on the specific points they are interested in.