REVIEW OF 16 FOREST-SOIL-ATMOSPHERE MODELS

The principles and characteristics of sixteen forest-soil-atmosphere m odels, describing the flows of water, carbon and nutrients in a forest ecosystem were compared. This comparison addresses technical aspects of model implementation and system discretisation, as well as the natu re of the included processes. A large variety of integrated models exi sts, but only a few of them are 'well-balanced', describing all aspect s of the forest ecosystem with a comparable level of detail. As a resu lt, only a few models can be used to assess effects of air pollution a nd acid deposition on forest growth. There is considerable agreement w ith respect to the description of the water cycle and geochemical proc esses; differences result mainly from different levels of process aggr egation. There is no general agreement on the description of the nutri ent cycle. Models differ most with respect to nutrient uptake and nutr ient (re)allocation in the plant. It is impossible to develop simple l umped models for regional, policy-oriented applications, without a wel l-based strategy for simplification. Therefore, simple models should a lways be backed up by more detailed mechanistic models, which can be t ested against field observations. Only a few models are well-documente d and available to others. The lack of concise and adequate model docu mentation hampers model exchange and may lead to unnecessary developme nt of new models. Therefore, model documentation must be given high pr iority.