Forest growth in relation to site conditions. Application of the model forgro 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 model that can be used to study effects of air pollution and soil acidification on forest growth for the Solling F1 site. Direct effects are quantified through stomatal uptake of air pollutants, and physiological effects of pollutant metabolites within the living tissue. Indirect effects are quantified through soil nutrient availability and conditions for root growth. Indirect effects determine the nutrient status of the trees, which in turn influences the susceptibility to direct effects of gaseous air pollutants. With the combined models, an analysis of combined effects of air pollution and soil acidification becomes feasible. Emphasis in the paper is on quantification of nutrient relations and growth, and the consequences of long-term changes in nutrient availability by soil acidification. In case of the Solling spruce site, the magnitude of the short-term, direct effects of air pollutants was found to be negligible, as was found elsewhere under comparable exposure conditions. Furthermore, it was investigated what effects of drastic changes in root characteristics were simulated. The model results indicate that the system is relatively insensitive to changes in rooting depth, but that uptake of nutrients strongly depends on soil moisture conditions.