Introduction

The primary aim of the inventorying process in the National Forest Inventory (NFI, abbreviated to WISL in Polish) is to assess the condition of Poland's forests under all forms of ownership and the trends in any large-scale changes that may be occuring in them. More specifically, the inventorying is to supply reliable information on forests, in particular regarding to the species and age structure, health status, and presence of damage. Furthermore, results of the NFI are an important source of knowledge on the site type structure, condition of young-generation specimens, current volume increments in stands and main-use fellings.

The work is carried out in line with the "Instructions for the National Forest Inventory" ("Instrukcja wykonywania wielkoobszarowej inwentaryzacji stanu lasu") approved by the Minister of the Environment of the Republic of Poland on 10 June 2010. These "Instructions" indicate that the requirement to engage in the work in question arose in particular out of a provision laid down in Art. 13a of Poland's Forests Act of September 28th 1991 (consolidated text in the Official Journal of Laws of 2014, item 1153, 2015 r. item. 349, 671, 1322).

Implementation of the NFI into the Polish forestry started in 2005. The NFI's first cycle covered the 2005–2009 period and was followed by the second cycle (years 2010-2014). Inventorying in the context of Poland's National Forest Inventory is done by the country's Bureau for Forest Management and Geodesy (Biuro Urządzania Lasu i Geodezji Leśnej), by virtue of a contract with the Directorate-General of the State Forests.

Results of the calculations are presented for forests categorized in regard to their form of ownership as:

1) under State Forests management,

2) under National Park management,

3) in the Treasury Agricultural Property Resource (managed via the Agricultural Property Agency),

4) other Treasury-owned,

5) local authority-owned,

6) private.

The total area of forest was determined using areal data relating to the different forms of ownership from the Central Statistical Office (Główny Urząd Statystyczny).

Methodology

The length of a full cycle of the NFI inventorying is 5 years. Measurements and observations are done each year on almost 20% of the sample plot clusters laid out across the whole country. The sample plot grid was based on the ICP Forest 16 × 16-km grid used for monitoring damage in forests. For the purposes of the National Forest Inventory, the grid density was increased to 4 × 4 km (Fig. 1).

 

Fig. 1. The overall configuration of sample plot grid

 

The different sample plots are laid out schematically, in a configuration of clusters distributed within the 4 × 4 km grid, in such a manner that each of the L-shaped clusters (in which both arms of the L are of equal length) comprises 5 sample plots located at a 200 m  distance from its closest neighbor. (Fig. 2). In Cycles I and II of the NFI a sample plot is deemed eligible for consideration if its center is located on land designated "forest" in the land register.

Fig. 2. The layout of a cluster as set against an exemplary division of an area

Measurements and observations are performed in two types of circular, concentric sample areas ("A" and "B" areas) whose size depends on the features being inventoried (Fig. 3). On the "A" areas, standing trees and shrubs are inventoried, be they alive or dead, providing that a 70 mm threshold in breast-height diameter has been reached. Lying dead trees are also inventoried, provided their thicker ends are of at least 100 mm in diameter, as well as stumps whose diameters without bark are equal to or greater than 100 mm. The "B" areas are used to measure and observe trees and shrubs with diameters under 70 mm. The radius of a sample plot depends on the stand age and structure.

Fig.3. Sizes of sample plots

Type A                                                                       Type B

r1 – radius   7.98 m, area 2 a                                     r4 – radius 0.56 m

r2 – radius 11.28 m, area 4 a                                     r5 – radius 2.59 m

r3 – radius 12.62 m, area 5 a

 

Results

The results of the National Forest Inventory presented here have been elaborated on the basis of data collected from sample plots in the years 2010–2014.  In the case of data concerning such features as volume increment or main use (felling) results have been elaborated by comparing data from Cycle I (2005–2009) to data from Cycle II (2010-2014). Comparison of the results between Cycles I and II of the NFI makes possible an assessment of the condition of Poland's forest and the trends for any large-scale changes that may be occurring in them.

 

units

NFI CYCLE I (2005-2009)

NFI CYCLE II (2010-2014)

overall

under State Forests management

private forests

overall

under State Forests management

private forests

Area of forests

ha

9 066 362

7 064 445

1 635 274

9 177 193

7 085 422

1 737 454

Forest cover

%

29.0

-

-

29.4

-

-

Growing stock

bln m3

2.304

1.849

0.342

2.469

1.95

0.403

Mean volume

m3/ha

254

262

209

269

275

232

Mean age

years

55

57

44

56

58

47

Volume of  dead trees

m3/ha

5.7

5.2

4.2

5.9

5.5

4.3

 

Data from the NFI measurements are a source of information that could be used in research on productivity, forest management, ecology, phytopathology, silviculture and forest protection.

Cycle III of the NFI

In Cycle III of the NFI which began in 2015, several changes to the "Instructions" have been made. Measurements in Cycle III are additionally taken also on the plots whose center is not located on land designated "forest" in land registers if they are located within an area covered by forest vegetation (forest area of at least 0.1 ha with a crown cover over 10%). These areas were not included to measurements in Cycles I and II of the NFI. Another change to the NFI "Instructions" is that all sample plots have the same area of 400 m2 and their dimensions are not dependent any more on the stand age and structure. Comparing the results of NFI between all the cycles is possible thanks to the fact that the basic assumptions of methodology have not been changed.