Nitrogen input in the forest
Nitrogen inputs are a serious burden on forests. Excessive nitrogen inputs result in imbalanced nutrition, root growth disruptions and nutrient absorption in trees. As a consequence, trees become more susceptible to diseases and pests. In the soil, excessive inputs cause acidification and nutrient leaching in addition to nitrate. This changes the quality of the soil over the long term. Eutrophication in forests generally occurs when there is an increase in nitrogen-loving plants such as elderberries and blackberries.
Forests continue to have high levels of nitrogen inputs. Since 2000, a decrease has been recorded only for oxidised nitrogen compounds, while inputs of reduced nitrogen compounds (NH3 from agriculture) have hardly changed. This is a direct result of emissions developments. Average nitrogen inputs in forests, which are 20.4 kg of N/(ha per year, 2015), are in excess of the critical loads for nitrogen. The exceedance of the critical loads in more than 95% of forests in Switzerland poses the potential threat of eutrophication and acidification.
The method underlying the indicator is an international standard.
Swiss-wide calculation by Meteotest, method described in: Rihm, B. and B. Achermann, 2016. Critical Loads of Nitrogen and their Exceedances. Swiss contribution to the effects-oriented work under the Convention on Long-Range Transboundary Air Pollution (UNECE). Federal Office for the Environment, Bern. Environmental studies no. 1642: 78 p.