The IAP has been monitoring forest health since 1984 on behalf of cantonal forest and environmental offices and in collaboration with the Federal Office for the Environment. In the Intercantonal Forest Observation Program (WDB) project, the health, growth and nutrient supply of beech, spruce and oak in managed forest ecosystems are studied on about 190 forest plots. The plots cover the most important gradients of Swiss forests, such as different climatic conditions in precipitation, temperature, as well as differences in soil and in the input of air pollutants such as nitrogen and ozone. Currently (date 2020) 94 plots with 6268 beech trees, 75 plots with 4547 spruce trees, and 50 plots with 1858 oak trees are surveyed in the Intercantonal WDB. Annual investigations include crown condition and tree loss by mortality, uprooting and stem breakage. Every 4 year stem increment is measured on all 12’673 trees and 8 branches are harvested by helicopter very 4 years and subsequently examined for the following parameters:
- Nutrient analysis in foliage (N, P, K, Ca, Mg, Mn)
- Leaf area and weight
- Shoot growth (retrospective for Norway spruce, beech and oak)
- Discoloration and parasite infestation
- Fructification of beech (retrospectively)
In addition, soil samples for analysing the chemistry of the solid phase are taken every 12 years. Also changes in the ground vegetation is assessed every 12 years. On a subset of the plots soil solution is sampled monthly (Soil solution monitoring of the Intercantonal Forest Observation Program). In addition, soil water potential and soil moisture are measured in a subset of sites of the Intercantonal Forest Observation Program (Soil moisture and soil water potential measurements of the Intercantonal Forest Observation Program).
These data allow to gain a unique understanding of the main factors influencing the forest and the most important changes, which are very valuable especially in the context of climate change. The insights are of great importance for cantonal and regional forest planning as well as for national and international determinations of critical loads and limits (e.g. CLempN, UNECE CLRTAP).
