FOREST GROWTH IN RELATION TO SITE CONDITIONS APPLICATION OF THE MODELFORGRO TO THE SOLLING SPRUCE SITE

A dynamic simulation model of forest growth (FORGRO) is combined with a general model of soil acidification (NUCSAM) to give an integrated m odel that can be used to study effects of air pollution and soil acidi fication on forest growth for the Selling F1 site. Direct effects are quantified through stomatal uptake of air pollutants, and physiologica l effects of pollutant metabolites within the living tissue. Indirect effects are quantified through soil nutrient availability and conditio ns for root growth. Indirect effects determine the nutrient status of the trees, which in turn influences the susceptibility to direct effec ts of gaseous air pollutants. With the combined models, an analysis of combined effects of air pollution and soil acidification becomes feas ible. Emphasis in the paper is on quantification of nutrient relations and growth, and the consequences of long-term changes in nutrient ava ilability by soil acidification. In case of the Selling spruce site, t he magnitude of the short-term, direct effects of air pollutants was f ound to be negligible, as was found elsewhere under comparable exposur e conditions. Furthermore, it was investigated what effects of drastic changes in root characteristics were simulated. The model results ind icate that the system is relatively insensitive to changes in rooting depth, but that uptake of nutrients strongly depends on soil moisture conditions.