Area calculation
Visiting sampling points
Sampling plots
The area associated with a sampling point is called the sampling plot, which is bordered by the circumference of the sampling circle. As the radius of a sampling circle is 12,616 m, the area of a sampling plot is 500 m2.
A sampling plot is divided into three concentric circles known as segments. The first segment is a circle with 3 m radius and an area of 28.274 m2. The first segment is a circle with 7 m radius and an area of 153,938 m2. The third segment is the full sampling plot itself (circle with a radius of 12.616, 500 m2 area).
Total forest land area
As only a fraction of the whole territory of the country is sampled directly and the data collected this way are extrapolated to country level, one should know the size of the area a sampling point represents. The smaller this area is, the more reliable the sampling and the more resources performing the job will require. Using the sampling grid and the tracts, it is easy to calculate that a sampling point comes to represent a total of 400 hectares by the end of the five year assessment cycle.
It follows from the above that total forest land area is proportionate to the number of sampling points located on forest land areas (number of sampling points × 400 ha).
Please, note that the area identified this way also includes plots classified as forest land areas that have not been assessed due to an obstacle. Such obstacles may include, for instance, floods, enclosed military area, etc.
The survey process
Area calculations are in each case based on sampling plots (500 m2). Data concerning territorial units of smaller size (segments) are extrapolated for the whole sampling plot. As regards the first and second segment, extrapolation is performed proportionately on the basis of segment size, while the data of the third segment refer to the sampling plot as a whole without extrapolation. Similarly, the General parameters, Dead wood volume and Stump data also pertain to the whole sampling plot, and need no extrapolation.
The data, which refer to a common territorial unit on the basis of the above (multiplied by 20) are used as inputs in other calculations. Calculations basically involve simple aggregation or reference to a territorial unit. An example of the former is the aggregation in hectares of the total area occupied by the tree species Quercus petraea (tree species area), whilst the country-wide territorial ratio of the same species an example of the latter and is calculated by projecting (%) the tree species area over the whole forest land area (ha).
Please note that tree species areas are derived from the summation of the areas occupied by sample trees of the same species. Sample tree area is expressed as a proportion of the sum of the disk area of sample trees to the total area associated with the sampling point. That is to say sampling points without sample trees are treated as "unstocked" areas, i.e. areas without forest cover.
The data of small trees form a special case, as small tree parameters are extrapolated to the whole sampling plot from data recorded in a circle with a radius of 3 m, nevertheless analytical statistics only summarise sampling points with at least 1 small tree. Such analytical statistics show, for instance, the per hectare number of small trees.