In 1993 the German Federal Environmental Agency initiated a project to evaluate the forest decline research of the period 19821992 in Germany. The project is interdisciplinary, including a plant physiologist, a soil scientist, a biologist, a geneticist, and a modeller. One aim is the evaluation of research results with methods of system analysis and the integration of quantitative and qualitative results in a simulation model. This procedure includes knowledge on interrelations and feedback processes of the manifold causes leading to forest decline.
The modelling of different and heterogeneous research results made it necessary to develop a model structure in which (i) single modules can be combined together, (ii) where different data sets can be easily included and (iii) different assumptions can be tested. Therefore the general requirements for the model are transparency and flexibility so that the combination of the different model levels should be comprehensible.
The soil compartment consists of several layers. All processes should be well-balanced, that means all processes are described in the same resolution. The technical application is easy to handle, and if required, the model is easily to extend. The user can chose between different assumptions not only for parameters but also for model structure. Within the model environment it is possible to test different assumptions quickly, which is of great advantage in testing different hypotheses related to the forest decline. The program language of the model is VisualBasicTM, it runs under Windows on PC´s.
Most of the hypotheses on the forest decline agree that tree nutrition is disturbed in some way. Therefore the GeneralSoilModule is closely related to the TreeNutritionModule and regards the special features of forest soils. All relevant processes are included as sub modules, like soil chemical equilibrium, cation exchange, weathering, sulfate adsorption, proton buffering etc.
Key words: forest decline, plant nutrition, system analysis.