Plot design
The standard procedure for soil sampling involves satellite sampling centred on a soil profile. As a rule, this centre point is permanently marked with a magnetic marker.
The exact determination of the NFSI center point is linked to the survey procedure for selecting sample trees in the National Forest Condition Survey (WZE). Usually, the center point of the NFSI sampling point coincides with the center point of the WZE cross-cluster. The center point serves as the reference point for all sampling and analyses to be conducted. The NFSI reference circle has a radius of 30 m, within which all surveys are conducted (sampling of humus and mineral soil, needle and leaf sampling, assessment of crown condition, stand inventory, and ground vegetation).
Idealised layout of a NFSI site
The standard procedure for soil sampling at the NFSI sampling points is satellite sampling, with a soil profile taken at the NFSI centre point. If possible, the soil profile should be dug, so that its end wall is located at the NFSI center and the profile pit is at least 1 m deep. The length of the profile pit needs to be adjusted to the depth, and the width of the vertically cut end wall should be at least 0.8 m.
Four boreholes are drilled as standart to sample the organic topsoil and the mineral soil, each located in 10 m distance to the centre point in the four cardinal directions. The boreholdes have a depth of 90 cm. If necessary, four additional boreholes are drilled between the four cardinal directions to a minimum depth of 90 cm and up to 140 cm if possible, to obian suffiient sample material for chemical analysis. Sampling of the topsoil and mineralsoil up to 10 cm is always coducted at all eight staellite points.
Needle and leaf sampling is conducted across the entire sampling area. Ground vegetaion is surveyed according to European standards within a uniform area of 400 m2. In addition, four satellites, positioned in 25 m from the center of each sampling point record the crown condition, using a sample of six trees (see here). For the studying of forest nutrition, needles and leaves from three samplin trees of each major tree species are sampled.
The Harmonized Stand Survey (HBI) (Hilbrig et al., 2014) serves as the foundation for recording the tree stand in the NFSI work instructions. Trees with varying diameter at breast height are recorded within three sample circles. Additionally, data on tree regeneration and deadwood are collected.
Some specific considerations must be taken into account for each federal state.
More detailed information can be found here:
- NFSI II Documentation: Thünen Working Paper 97 (German language): National Soil Condition Survey in Forests – Documentation and Harmonization of Methods
- NFSI III Work Instructions (German language): Thünen Working Paper 195