To What Extent Can Silviculture Enhance Sustainability of Forest Sites under the Immission Regime in Central Europe?

Stand structure and tree species composition influence not only the volume flux of soil water but also the concentration of dissolved minerals in the soil solution. We found much higher element fluxes under spruce than under beech stands. This is mainly caused by different activities of nitrate in the soil solution and by different deposition rates of nitrogen and acids from the atmosphere which were ±60% lower in beech stands than in spruce stands. In old spruce stands, the acid output with the seepage water was more or less equal to the input, whereas in beech stands most of the acid deposition was buffered. The nitrogen balance in beech stands was characterized by a net uptake of about 60% to 75% of the input. In spruce stands only 40% of the nitrogen input was incorporated. In a clear-cut, a high mobilization rate of nitrate was found in the first 5 years, resulting in nitrate concentrations above the threshold for drinking water quality. The cutting of even a single tree in a spruce stand caused heavy mineralization and nitrification for at least 2 years, which indicates that the system is near nitrogen saturation.