Sampling design

The National Forest Soil Condition Inventory (NFSI, German: BZE) is a systematic sampling survey. The NFSI sampling grid covers the entire forested area of Germany. In principle, only sample units (NFSI points) within the forested area are sampled.

The NFSI III is conducted on the nominal 8 x 8 km sampling grid, with at least the NFSI II points being processed. Studies have shown that this minimum density is necessary to enable spatially differentiated and area-representative conclusions at the national level. State-specific issues often even require regional and thematic densification of the base grid. The total size of the NFSI sample in Germany is approximately 1,900 survey points (NFSI II: 1,859 points).

Nevertheless, in the run-up to the NFSI II, it was examined whether the sample size – and thus the workload – could be reduced through pre-stratification. The term pre-stratification refers to the preliminary division of a study area into homogeneous sub-areas prior to the actual data collection. Ultimately, pre-stratification (e.g. based on field soil characteristics) was not adopted, as it cannot be assumed without reservation that field soil units correlate with soil chemical properties. This assessment remains unchanged. To enable an integrated analysis of soil data, needle/leaf analyses, forest floor vegetation and crown condition assessments, the NFSI was generally incorporated as a sub-sample into the grid of the Forest Condition Survey. Consequently, the sampling points of the NFSI are generally identical to those of the Forest Condition Survey (WZE) and the Immission-Ecological Forest Condition Survey (Immissionsökologische Waldzustandserfassung - IWE).