The RReShar model (Regeneration and Resource Sharing), implemented within the CAPSIS simulation platform (http://www.inra.fr/capsis/), is a functional structural model. Stand structure is described including all the strata of the forest ecosystem, i.e. adult trees, suppressed trees, saplings and seedlings growing in the understorey (regeneration) and herbaceous/shrubby vegetation. Growth processes of all those components are based on the interactions for light and water. The simulated scene is a 1 ha plot divided in square cells of chosen size (of a few meters). Adult trees are explicitly spatialised on the plot, whereas understorey vegetation and regeneration are considered as a multi-species layer which characteristics vary at the cell level. Vegetation is described by its height, cover and porosity. Tree regeneration, i.e. seedlings and saplings, are initialised as cohorts characterized by a diameter and height distribution. Overstorey and understorey growth time step is annual, whereas within this annual loop, the light interception and water cycle (interception and evapotranspiration) processes are respectively monthly and daily simulated. Currently, RReShar is calibrated with data coming from uneven-aged mixed Quercus petraea Pinus sylvestris stands with an understorey colonised by Calluna vulgaris, Pteridium aquilinum and Molinia caerulea in temperate conditions.