# The principle of NFI evaluation

Each sample plot (sample point) comprises a certain part of a total evaluated area, which is called a representative plot. Information gathered from individual sample points within an evaluated area is transferred into the NFI estimation by the weight (sampling weight), which corresponds to the size of the relevant representative plot. This consideration is essential to the NFI evaluation.

## Brief information about NFI evaluation procedures

A brief introduction to the NFI sample surveys can be found in the presentation entitled Methodological principles of the NFI (in Czech), held at the 80th anniversary of ÚHÚL‘s foundation. A more detailed lecture on the principles of mathematical and statistical evaluation of the NFI is available in the form of a presentation for students (in Czech) of the Faculty of Forestry and Wood Technology at the Mendel University in Brno.

Readers seriously interested in sample surveys can benefit from presentations on a local density function (in Czech) and one-phase estimation (for continuous populations; in Czech). Within the international project USEWOOD, a training on statistical methods in the NFI was organized, where a presentation on two-phase estimation was given. The above presentations served as material for broader lectures. This is why they contain a wider range of methods that do not usually correspond to the specific situation of the NFI2 evaluation.

## Evaluation methodology of the NFI second cycle (2011–2015)

The NFI2 statistic evaluation methodology is available online:

- one-phase estimation of a total and a ratio (in Czech)
- one-phase estimation of a difference of two ratios

There were written two expert opinions on the methodology:

- opinion by Dr Adrian Lanz (a Swiss NFI statistician, Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft / WSL)
- opinion by Prof. Jaromír Antoch, Dr Zdeněk Hlávka and Dr Zbyněk Pawlas (Charles University in Prague, Faculty of Mathematics and Physics, Department of Probability and Mathematical Statistics, in Czech)

Both the opinions confirmed that the methodology used was correct.

## Methodological development after the NFI second cycle

The NFI third cycle started in 2016 and because it is continuous, evaluations for shorter periods (e.g. a particular year) and/or for smaller areas are required. These requirements can only be met using auxiliary data sources, mostly obtained by remote sensing methods, as the size of the sample is reduced (number of sample plots assessed in a given period or area).

Therefore, a regression estimation methodology was developed, which was first used in the H2020 Diabolo project. Within the project, a prototype of an information system (nFIESTA – new Forest Inventory Estimation and Analysis) was designed, implemented and successfully tested by a case study (above-ground biomass estimates using the integrated database of the French, German, Swiss and Czech NFIs). A complete overview of the status and development of the nfiesta system and related methodology can be found in the relevant Diabolo project report.