Within each species, the biomass is divided into live, standing dead and litter material, and further split into digestibility classes. If radiation data are not available, they can be computed from sunshine hours or from temperature and the coordinates of latitude and longitude. Some pastures consist of a number of populations of different species or cultivars. Phenology is modeled by following each species through a number of stages. After vernalization, the plant enters the vegetative stage.
Perennial grasses can exhibit a period of dormancy after reproduction finishes.
In annuals, a senescent phenostage follows reproduction until a germination event occurs and the developmental cycle restarts. Death rates of live biomass depend mainly on whether the end of the growing season has been reached. Standing dead biomass falls to the ground and becomes litter. The specific rate of fall of standing dead into the litter pool is modeled as a function of trampling and rainfall. Digestibility changes are governed by temperature and moisture and are modeled with separate equations for green, standing dead and litter.