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- Boden; Wald; Inventur; Probenahme; Karten; Konzentrationen; Vorräte; Kohlenstoff; Stickstoff; pH-Wert; Trockenrohdichte; Unsicherheiten; Harmonisierung; Repräsentativität (1)
- Soil; Forest; Monitoring; Inventory; Sampling; Mapping; Stocks; Concentrations; Carbon; Nitrogen; pH-Value; Bulk density; Uncertainties; Representativity; Harmonisation (1)
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The productivity of forest ecosystems depends on the supply of both nutrients and water by soils. Therefore, the knowledge of the chemical and physical soil properties is crucial for assessing the soil
condition as well as the quality of forest sites. For this purpose, data are available from two nationwide Forest Soil Inventories (NFSI) on more than 1,800 sample plots of an 8 x 8 km grid. The inventories were conducted between 1986 and 1994 (NFSI I) and 2006 and 2009 (NFSI II) in accordance with harmonized surveying techniques. The LUCAS Project aims at the development of a harmonized dataset on land cover
and land use within the European Union (EU). Approximately 265.000 georeferenced plots on a 2 x 2 km grid were available from the European Soil Data Centre (ESDAC). Soil samples were taken in 2009 and in 2015 at approximately 10 % of these plots at the same locations. Considering two almost parallel running soil inventories, questions have arisen to their potential links to one another. In this study, the LUCAS soil data from the 2015 inventory were compared with the corresponding NFSI II data and reviewed under the aspect of representativeness. In order to enable an area weighted estimation for Germany the plots of the LUCAS program were attributed to the same 16 soil parent material groups used in the German NFSI data
using geographical coordinates. All classes were tested for significant and systematic differences between the inventories. To quantify C stocks, it is important to compare the depth level 0-20 cm of the LUCAS program to Germanies NFSI sampling scheme, where data available for the organic layer and the mineral soil down to 90 cm. The comparison of various chemical soil parameters showed clear differences between the inventories. The pH(H2O) and the C/N ratio derived from LUCAS 2015 was lower while carbon (C) and nitrogen (N) concentrations were higher compared to the NFSI II. The C and N stocks deviate even more from the NFSI II due to uncertainties in the estimation of bulk densities derived from maps. By contrast
Germany’s NFSI, were volume-based sampling was obligatory for almost all plots. As a result, fine earth stock estimates from map derived bulk densities could result in highly uncertain and overestimated stocks change rates. Higher C and N concentrations of the LUCAS inventory could be attributed to an insufficient separation of the organic layer from the mineral soil because if the separation is not practiced carefully, residues of the organic layer can contaminate the mineral soil sample and cause significant higher concentrations. The soil sampling of the NFSI focused explicitly of the systematic separation of both compartments. The number of the sampled forest plots of LUCAS 2015 showed a lack of representativeness because in the northern and southern parts of Germany an insufficient number of plots were sampled. Nevertheless, the proportion of the forest area of the total LUCAS inventory is comparable with Germany’s Third National Forest Inventory. The selected LUCAS 2015 samples comprise 25 % of the NFSI II plots which results in an insufficient coverage of various soil groups. This means that soil properties remain unconsidered and that the area-weighted extrapolation could become more difficult. Chemical soil parameter within in individual substrate groups differed between the sampling grids due to the smaller sample of LUCAS 2015 compared to the NFSI II. Moreover, the reduction of sampling plots results in an increase of uncertainties. Thus, the detection of changes in soil conditions could be more difficult in respect to repeated sampling. Soil inventory data are of importance in greenhouse gas reporting because C stocks the organic layer and the mineral soil down to 90 cm must be reported. The analysis of the NFSI II revealed
that the organic layer comprises 16 % of the C stored in the entire soil profile. The organic layer was not sampled in the LUCAS inventory. Nevertheless, changes in C stored in the organic layer is vulnerable to impacts of climate and other environmental and anthropogenic variables but the effects cannot be considered with LUCAS 2015. Due to the LUCAS 2015 mineral soil sampling depth down to 20 cm only 42 % of the stored C was detected in the entire soil profile. Therefore, data based on LUCAS 2015 are insufficiently qualified for the greenhouse gas reporting due to the lack of a sampled organic layer and the limitation to the sampling depth of 20 cm. Compared to Germany’s NFSI, the results based on the LUCAS
inventory revealed a smaller representativity and were associated with larger uncertainties as well as discrepancies. Consequently, the union of both data sets will not result in additional synergies.