Deviances from expected Ellenberg indicator values for nitrogen are related to N throughfall deposition in forests

The indication of environmental changes and their impacts on various compartments of ecosystems are high on the political and scientific agenda. Spatially and temporally different inputs of eutrophying nitrogen compounds into European forest ecosystems and their effects are still of concern. Tending floristic changes and respective changes of nitrogen indicator values are one of the suspected effects. Those can, however, not easily be discovered within any cross-sectional short-term approach. Since continuous long-term observations with a sufficiently large sample on an adequate geographical scale are not available, the investigation of deviations from a rather balanced and scientifically settled relationship between the soil acidity status and N mineralization rate is used to indicate additional nitrogen supply from atmospheric inputs. The suspected deviances show a significant statistical relationship with total N throughfall deposition (to a lesser degree also with oxidised and reduced nitrogen compounds), measured at the same locations. This suggests a higher N availability at sites with greater N deposition rates, causing a disproportion between site-specific mineralization rates and the effective amount of plant available nitrogen. In spite of some minor methodological restrictions, the approach might be an appropriate means to localise and regionalise eutrophying effects from atmospheric deposition of nitrogen on larger scales.