Grassland productivity can be estimated using individual-centred models or via crop simulators parameterized to mimic average morphological and physiological features of the phytocoenosis as a whole. Although the latter is often considered an oversimplified solution, individual-centred models are characterized by a degree of complexity that often restricts their use to scientists specialized in pastures modelling or in crop-weed interaction. In this study, an intermediate solution is presented (CoSMo), based on two assumptions allowing the use of a single instance of a generic crop model to simulate phytocoenosis dynamics and productivity. The first is that community parameters can be derived at each time step from the relative presence of the different species and from parameter values determined for the species in monoculture. The second is that inter-specific competition and changes in species relative presence can be simulated as a function of species-specific responses to hierarchically arranged drivers (triggered and continuous) representing the suitability of the different species to the conditions explored at each time step. CoSMo was here analyzed by means of three simulation experiments, where changes in the relative presence of three species with different traits and the productivity of the community were simulated under current conditions and future climate projections. Results encourage further studies, given that the solution proposed is easy to implement and parameterize, and leaves users free to work with the generic crop simulator they are familiar with. These features make CoSMo suitable for being coupled – within integrated studies – to models developed for other domains by scientists not specialist in the ecophysiological aspects involved with inter-specific competition. However, this approach cannot be considered as an alternative to individual-centred models in case of in silico studies explicitly focusing on the relationships between inter-specific competition and species traits and phenotypic plasticity.