Modelling of soil characteristics as basis for projections of potential future forest ecosystem development under climate change and atmospheric nitrogen deposition

The EU Biodiversity Strategy to 2020 foresees that Member States assess conditions and potential developments of ecosystems under climate change and atmospheric nitrogen deposition. This combination of environmental impacts has never been modelled for the German territory before. Therefore, the aim of the presented dynamic modelling of soil parameters under the influence of changing atmospheric nitrogen deposition with simultaneous climate change at representative sites in Germany was to derive knowledge about the expected development of ecosystem conditions up to a possible change of the respective site-specific current ecosystem type. The dynamic modelling was performed with the Very Simple Dynamic soil model. The selection of 15 modelling sites regarded the availability of data from environmental monitoring programmes routinely operated by public institutions and the aptitude of data for parametrising the soil model. The most important input data are time series of nitrogen and acid deposition as well as time series of the relevant climatic-ecological parameters. The simulation period covered the years 1920–2070. There are no continuous linear correlations between the level of acidifying or eutrophying inputs and the course of soil parameter values. The step-like courses result from the resilience of the ecosystems within certain parameter ranges. Atmospheric nitrogen deposition has led to nitrogen saturation at 14 of 15 sites selected for modelling. Currently, no linear (negative) correlation between nitrogen deposition and carbon/nitrogen ratio could be established at these sites any more. An increase in the N-content in the soil was only slight, if at all. On the other hand, the nitrate concentration in the leachate increases in correlation to the N deposition. A clear (negative) correlation was found for the dependence of the C/N ratio on the temperature development in connection with climate change. The predicted air temperature rise until 2070 will also cause a decrease of the carbon content in the future, caused by the increasing activity of decomposing soil organisms. Thus, the drastic decrease of the C/N ratio at all of the study sites is due to the significant decrease in the C content. The validation shows that the dynamic modelling of abiotic site parameters has delivered plausible results at the investigated sites. The applicability of the results could be demonstrated. Thus, the evaluation of the time series of soil and climate parameters resulted in forest ecosystem types that are capable of self-regeneration in the future under the conditions of air pollutant inputs and climate change. The dynamic modelling of soil parameters under the influence of atmospheric nitrogen deposition and of climate change enables to transparently rank the potential development of ecosystem conditions up to a possible extinction of the current ecosystem type. Thus, the soil modelling approach presented contributes to the implementation of the European Biodiversity Strategy.