Structure of the sample plots
|1||Circular area for the survey of woody plants with dbh ≥ 12 cm (200 m²)|
|2||Circular area for the survey of woody plants with dbh ≥ 36 cm (500 m²)|
|3||Circular areas for the regeneration survey
Height class 10–39 cm: 2.5 m²
Height class 40–129 cm: 7.1 m²
dbh class 0.1–3.9 cm: 19.6 m²
dbh class 4.0–11.9 cm: 50.3 m²
|4, 5, 6||Transects for the survey of lying deadwood and soil damage|
|7||Interpretation area for stand and site attributes (50 m × 50 m)|
|8||Forest boundary line (FBL)|
|Aerial photo raster points|
|Raster point outside FBL|
|Raster point on stocking element|
|Raster point on other land cover|
Each NFI sample plot consists of several subplots on which different attributes are surveyed:
Terrestrial survey (on accessible forest sample plots):
- All trees and shrubs with a diameter at breast height (dbh, 1.3 m height) ≥ 12 cm are recorded within a 200 m² circle around the sample-plot centre, and all those with dbh ≥ 36 cm are recorded within a 500 m² circle. The radii of the circles are 7.98 m and 12.62 m on level terrain.
- In concentric circles with areas of 2.5 to 50.3 m² located at a distance of 10 m from the sample-plot centre, trees and shrubs with dbh < 12 cm but plant height ≥ 10 cm are recorded (‘regeneration survey’).
- Along three 10 m transects, deadwood lying on the ground (≥ 7 cm diameter) and soil damage are recorded.
- Within a 50 m × 50 m square area (interpretation area), stand attributes (e.g. development stage or degree of mixture) and site attributes (e.g. traces of natural hazards) are considered.
Aerial photo interpretation (all sample plots):
- At 25 raster points within the interpretation area, land cover type and surface elevation are determined on the aerial photo. In addition, the forest boundary line (FBL) is determined for sample plots near the edge of the forest.