Evaluating Forest Soil Health in Europe Using ICP Forests Data and the SHERPA Framework

Soil health degradation is a major threat to European forests, with consequences for biodiversity and climate stability. Although spatially distributed soil data are available, a clear and quantifiable framework for soil health monitoring, management, and policy support is still lacking. In this study, we applied the recently proposed SHERPA framework (Soil Health Evaluation, Rating Protocol, and Assessment) to ICP Forests Level I data. SHERPA was published as a framework for discussion and provides the first quantitative soil health assessment at the European scale (Alewell et al., 2025).Soil health scores were estimated by considering all major soil degradation processes, which were averaged to obtain Part 2 scores. This value was then subtracted from the intrinsic soil health score (Part 1), which is based on altitude, parent material, and humus horizon thickness (OL, OF, and OH), to calculate the final quantitative soil health score. Preliminary results indicate that soil health in forests across Europe is significantly reduced. This is mainly driven by nitrogen surplus, reflecting the widely documented forest decline caused by nutrient imbalances. Soil health is further affected by soil erosion and elevated concentrations of heavy metals, particularly nickel, which are predominantly observed in southern Europe. Overall, 45% of the samples show soil health scores below 1 on a scale from -8 to 10. These results are based on coarse-resolution spatial data due to the limited availability of measured soil data, especially of information on soil compaction and/or disturbance of a closed humus layer coverage of the soil. Therefore, the estimates can be further improved, but they already highlight major threats to forest soil health across Europe.