Forest inventory
Forest inventories are systematic data collections of a certain area of forests. Data can be collected using the sampling method (on permanent sample plots) or plot-wise (stand descriptions). Forest inventories are an integral part of forest planning; based on the analysis of the obtained data, with which we determine the state of the forests and their changes over time, as well as the influencing factors, we decide on future measures in the forests.
We roughly distinguish between 1) the collection of data on forests for the preparation of forest management plans and 2) the national forest inventory, which is primarily intended for forest policy and international reporting.
Forest inventories for the preparation of forest management plans
The collection of data on forests for the purpose of elaborating forest management plans is carried out during regular revisions of the forest management plans of forest management units (FMP FMU), which are prepared for a period of 10 years.
Measurement on permanent sample plots
During the regular revisions of the FMP FMU, data on forests is collected on a systematic network of permanent sample plots and in the process of descriptions of stands. The data collected on almost 100,000 permanent sample plots (PSP) allow a detailed insight into the state, development dynamics and biodiversity of forests. They are intended for the calculation of key stand parameters, such as growing stock, ingrowth and cut, tree species composition, deadwood and others. The most frequently used sample grids in Slovenia are 250 m × 500 m, 200 m × 500 m and 250 m × 250 m.
Each plot is measured once every ten years, namely when the FMP FMU is renewed. The centre of the plot is marked with a geodetic stake or an iron stick 30 cm long (in the ground). The plot consists of two concentric circles. In the inner circle (200 m2), all trees are measured, and in the outer circle (500 m2) only trees with a breast diameter (1.3 m above the ground) of 30 cm and more. Measured trees are marked with a short horizontal notch in the bark. The main measurement parameters are: tree species, old and new diameter, social status of trees, quality and damage, hight of the dominant trees etc.
Information on measurements on permanent sampling plots are available here (in Slovene): https://www.youtube.com/watch?v=uswkaxRjHmU
Stand descriptions and stand map
The description of stands is the process by which stands are delineated on the basis of stand characteristics, their condition is described, and at the stand level we also preliminarily plan measures for the next decade. Main parameters that are defined during the stand descriptions: forest stand structure / developmental phase, quality of stand potential, cohort opening, state of regeneration, stand tending state, tree species composition, growing stock, allowable cut, forest silviculture and protection works, other measures.
There are more than 320,000 delineated forest stands with associated data on the state of forest stands, directions and planned measures at the stand level. They are shown on the stand map, which is accessible with other important data layers on forests, including forest management and hunting management plans, on the Slovenia Forest Service viewer. Forest stand map is prepared for all forests in Slovenia regardless of their ownership.
Information on stand descriptions is available here (in Slovene): https://www.youtube.com/watch?v=GsB-RK7rwHI
National forest inventory
At the national level, the main source of data on forests is usually the National Forest Inventory (NFI), which is carried out independently of measurements for the needs of forest management planning.
About NFI
The NFI is an integral part of the national forest monitoring system and is a technical data collection process that provides unbiased estimates of selected variables on forest characteristics (e.g. basic such as number of trees, diameter structure, tree heights, species composition, and indirect such as growing stock, increment, etc.). To these basic parameters, a number of other parameters describing the forest (tree quality, tree age, dead biomass, carbon stock, regeneration, etc.) are added within the framework of NFI. The basic purpose of the NFI is to provide a statistically correct assessment of the state and changes of selected forest parameters for the needs of forest policy and international reporting.
NFI in Slovenia
The NFI system in Slovenia, as abroad, represents large-scale monitoring of forests, which means that it is used to obtain temporally and spatially defined data on the condition of forests at the national level with known statistical reliability. The NFI was established in Slovenia in 2020 on an irregular systematic sampling grid with a density of 2 km x 2 km. Methodologically, it represents the upgrade of the Monitoring of Forests and Forest Ecosystems (MGGE) system, within the framework of which plots were measured on a 4 km x 4 km systematic sample network in the years 2000, 2007, 2012 and 2018.
Measurements at NFI in Slovenia are carried out by the Slovenian Forestry Institute in cooperation with the Slovenia Forest Service and the Ministry of Agriculture, Forestry and Food.
Data
All detailed information about this inventory and NFI results can be found on the website of the Slovenian Forestry Institute: link.
Each year, based on NFI data, a report on monitoring the state of forests is prepared, which is available at https://www.gozdis.si/publikacije.
A publication on changes in forests between 2000 and 2018 was also prepared: DiRROS - State and changes of Slovenian forests between 2000 and 2018: results of large-scale monitoring of forests and forest ecosystems (openscience.si).
