Background and History
Forest soils form the basis for healthy and resilient forests.
They supply water and nutrients for forest growth, buffer pollution and acid deposition, and compensate for water shortages during dry periods. Forest soils thus play a crucial role in climate protection and also make an important contribution to biodiversity (Wellbrock et al. 2016).
The current condition of forest soils is the result of long-term natural developments as well as anthropogenic influences (Blume et al. 2010). As a result of centuries of human use, forests have been subjected to significant nutrient loss, e.g. through slash-and-burn, forest grazing, clear-cutting and the associated soil erosion.
Today’s forests are largely the result of silvicultural decisions, with stand structure and the choice and mix of tree species playing a particularly significant role. Above all, these factors influence the quantity and distribution of organic matter in the soil, material cycles, deposition processes and the acid-base balance, as well as the forest climate and water balance (Wellbrock et al. 2016).
Following the debate on forest damage, the National Forest Soil Inventory (BZE) has been an integral part of forest environmental monitoring since the late 1980s.
Development of the BZE
In the context of the debate on forest damage, the nationwide soil condition survey was established in the late 1980s and early 1990s, alongside crown condition monitoring.
Following the Chernobyl nuclear disaster, the field surveys for BZE I took place between 1989 and 1992. The results were published in 1996: The findings of the BZE I survey revealed ‘widespread, largely substrate-independent acidification and depletion of bases in the topsoil, as well as a tendency for the chemical condition of the topsoil to stabilise at a low level’ (Wolff & Riek 1996). View the results of the BZE I here.
Since the 1990s, sulphur deposition from fly ash has declined as a result of cross-border air pollution control measures (UNECE 1979), although nitrogen deposition has remained constant. Lead was banned from petrol. The results of BZE II reflected the changed environmental conditions. Soil conditions had recovered slightly. The pH value rose slightly and the nutrient status had improved. Heavy metal concentrations in the soil, particularly lead, had also decreased. However, the water balance of the forests revealed an increase in the number of dry years between 1990 and 2006. Carbon storage is within the range of the above-ground biomass.
The BZE II survey was conducted between 2006 and 2008, providing for the first time a spatially representative overview of changes in forest soil condition over a period of approximately 15 years. The scope of the study was significantly expanded, and a set of guidelines was agreed upon in advance between the federal government and the states. The BZE II report was published in 2016. View the results of the BZE II here.
The BZE III survey was carried out between 2022 and 2024: around 50,000 samples were taken at approximately 2,000 sampling sites, which are now being analysed. The federal report is due to be published at the end of 2028.
Division of responsibilities
Forest environmental monitoring, and thus also the NFSI, is carried out jointly by the federal and state governments in Germany.
The data is collected by the federal states. The evaluation of BZE II was carried out in cooperation between the Thünen-Institute, which compiles the data for nationwide analysis, representatives of the state forestry research institutes, environmental authorities and external experts. Specialised analyses of heavy metals and organic pollutants are carried out by the Federal Institute for Geosciences and Natural Resources and the Umweltbundesamt (Wellbrock et al.).
The federal states’ forestry research institutions install the monitoring network, carry out data collection and compile state-level datasets, as well as analyses and reports. The collection and state-level analyses are generally funded by the federal states. At federal level, the forestry research department of the BMLEH (until 2008 the Federal Research Centre for Forestry and Forest Products (BFH), since then the Thünen-Institute) is responsible for coordinating the inventories, processing, analysis and reporting of a comprehensive dataset.
Reporting obligations to the UNECE or the EU are fulfilled by both the federal states and the federal government.