Sampling design

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

The BZE III is conducted on the nominal 8 x 8 km sampling grid, with at least the BZE 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 BZE sample in Germany is approximately 1,859 survey points (BZE II: 1,859 points).

Nevertheless, in the run-up to the BZE II, it was examined whether the sample size – and thus the workload – could be reduced through pre-stratification. 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 BZE was generally incorporated as a sub-sample into the grid of the Forest Condition Survey. Consequently, the sampling points of the BZE are generally identical to those of the Forest Condition Survey (WZE) and the Immission-Ecological Forest Condition Survey (Immissionsökologische Waldzustandserfassung - IWE).