Résumé
Phenotypic plasticity is defined as the plastic responses of plant phenotypes to the abiotic and biotic environment. Very little is known about the consequences of phenotypic plasticity for plant communities in general, and agroforestry systems in particular. We put in evidence key aspects of plasticity in some temperate agroforestry systems, including the dramatic distortion of the tree root system as influenced by crop competition or the asymmetric extension of the tree canopy in wide-spaced tree plantations. More subtle aspects of plasticity may also be operating such as the adaptation to shade of ecophysiological processes for crops. Models should incorporate plasticity mechanisms to account for the outcomes of agroforestry systems. However, most process-based models do not account explicitly for plasticity mechanisms. Crop models or tree-based models usually do not take into account such processes. We incorporated in the Hi-sAFe process-based model of agroforestry systems, plasticity formalisms for tree balance and growth, both above and below-ground. An opportunistic tree root growth was obtained with the use of a 3D voxel automata. Some aspects of canopy plasticity were poorly explained, such as the reduced east west canopy extension of north south aligned trees. A virtual experiment plan was then performed to explore the sensitivity of the system to the phenotypic plasticity of trees by comparing simulations including or excluding plasticity