WORKSHOP ON COMPARISON OF FOREST-SOIL-ATMOSPHERE MODELS - PREFACE

Between 10 and 14 May 1993, a workshop was organized in Leusden, the N etherlands, in which the concepts and performance of 18 models were di scussed. These models were generally aimed at the analysis of effects of acid atmospheric deposition on forest and forest soils. Model conce pts were analysed by means of a questionnaire. Model performance was a nalysed by application of the models to a common dataset for the F1 No rway spruce site, at Selling, for the period 1970-1990. The nature of the participating models varied widely, but all models were process-or iented and dynamic. Included were hydrological models, soil chemistry models as well as integrated models for calculation of forest growth. Overall, average annual hydrology, soil solution chemistry and forest growth of the spruce site between 1970-1990 could be reproduced. Diffe rences between models were attributable more to different parameteriza tions than to differences of model concepts. Short-term temporal dynam ics of soil solution chemistry were not reproduced very well, particul arly for nitrate. Models also gave different predictions of the respon se of the Norway spruce to maintained or reduced fluxes of atmospheric deposition, however, confirming a key role for Mg and N. Complex mode ls did not give better results than more simple models. Integrated mod els were also judged unbalanced, with respect to description of the hy drologic, soil chemical and forest subsystems. Therefore, it was recom mended to improve this balance and to work towards less complex models for prediction of the long-term behaviour of forest stands. Our knowl edge about nutrient uptake by forests in nutrient-limited acidified so il systems, and also about the interaction of various forest stresses is still inadequate. Future research should therefore emphasize a bett er integration of model development and experimental research, e.g., a s presently is the case for experimental field manipulations.