Modélisation des relations entre la diversité et le fonctionnement de couverts prairiaux à flore complexe

Modelling the relationships between the diversity and the functioning of pasture swards with a complex floristic composition

Within the framework of the 'DISCOVER' project (ANR Bio-diversity), the relationships between the bio-diversity and the functioning of pasture swards with a complex floristic composition are being studied in long-duration experiments. The data supply parameters and the means of evaluation for setting-up a mechanical model (GEMINI) that simulates the dynamics of the plant species and its consequences on the production and the quality of the herbage, and also on the workings of the soil. For the plants competing among themselves within the sward, GEMINI calculates the interception of light and of nitrogen, as well as the morphology of the above-ground parts and of the roots. The first modelling studies had borne on the simplified case of sown grass-clover associations. The present ambition of DISCOVER is to apply the model to swards with a complex floristic make-up, constituted by voluntary species, generally less well known. The effects of the number and of the type of species on the productivity of the pastures have been simulated, taking into account their plasticity of form and of function. Three examples of results are given. They concern : the role of the plasticity of leaf features in the response of grasses to nitrogen; the role of etiolation in the response of a dicotyledon to shade; and the role of the number of species and of functional groups in the productivity of the pasture. The applications of the model concern the role of bio-diversity in the ecological benefits of pastures with a complex floristic composition, and the simulation of the impacts of the climatic change.