Application of pnet-cn/chess to a spruce stand in Solling, Germany

The forest-soil-water model pnet-cn/chess was applied to an intensive data base available for a spruce stand at Solling, Germany. Model results of hydrology, forest growth (net primary production of foliage, wood and fine roots) and element cycling, as well as soil and drainage water chemistry generally showed good agreement with measured values. pnet-cn/chess was able to predict average concentrations and the increases of NO^-₃ in Solling drainage waters over the 20-year study period (1970-1990), but was not able to simulate some of the dynamics in the overall record. A minor discrepancy between measured and predicted concentrations of SO^2-₄ seems to be attributed to a missing source of S in the ecosystem S budget. Model calculations were not able to predict a large decline in pools of exchangeable basic cations observed at the site. Hypothetical simulations of the impact of atmospheric deposition on drainage water chemistry suggest that the Norway spruce (Picea abies) site at Solling is experiencing conditions of N saturation. Future decreases in S and N loading will likely result in marked declines in leaching losses of SO^2-₄ and NO^-₃, causing an increase in pH.