Workshop on Comparison of Forest-Soil-Atmosphere Models: Preface

Between 10 and 14 May 1993, a workshop was organized in Leusden, the Netherlands, in which the concepts and performance of 18 models were discussed. These models were generally aimed at the analysis of effects of acid atmospheric deposition on forest and forest soils. Model concepts were analysed by means of a questionnaire. Model performance was analysed by application of the models to a common dataset for the F1 Norway spruce site, at Solling, for the period 1970-1990. The nature of the participating models varied widely, but all models were process-oriented 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. Differences between models were attributable more to different parameterizations than to differences of model concepts. Short-term temporal dynamics of soil solution chemistry were not reproduced very well, particularly for nitrate. Models also gave different predictions of the response of the Norway spruce to maintained or reduced fluxes of atmospheric deposition, however, confirming a key role for Mg and N. Complex models did not give better results than more simple models. Integrated models were also judged unbalanced, with respect to description of the hydrologic, soil chemical and forest subsystems. Therefore, it was recommended to improve this balance and to work towards less complex models for prediction of the long-term behaviour of forest stands. Our knowledge about nutrient uptake by forests in nutrient-limited acidified soil systems, and also about the interaction of various forest stresses is still inadequate. Future research should therefore emphasize a better integration of model development and experimental research, e.g., as presently is the case for experimental field manipulations.