ALWAYS: a plot-based silvopastoral system model

Accounting for interactions is an important feature in ecological modelling when dealing with complex systems. ALWAYS is an object-oriented model which describes the biophysical functioning of a silvopastoral system at a plot and daily scale. The main processes linking the five components of the system (climate, tree, sward, soil and animal) are described. The interactions processes between the different components of the system are taken into account and resources sharing is modelled. The main biophysical equations are developed (tree and sward growth, water cycle, transmitted PAR). ALWAYS offers three ways of running it: (i) interactively by running the simulation year by year and checking results at the end of each year using graphs and output files; (ii) automatically by describing the management over the full tree rotation and (iii) in a sensitivity analysis mode to test parameters from the yearly or rotation outputs. Examples of output files, written in an ASCII format, are provided. Such a model is the first step towards a more effective decision support tool.