## 2 Materials and Methods
### Data Sources
The old military topographical maps are probably the data source that provides the most information about the objects of the area that existed before. The creation of military topographic maps began in the territory of Lithuania in the 19 th century after the installation of triangulation networks [56]. Later, the territory was mapped out several more times, including during the 1 st and 2 nd halves of the 20 th century. The outlines of the depicted forest areas are generalized due to map generalization and area mapping methods, but the generalization process does not lead to significant losses of the mapped-out forest areas. Therefore, it can be stated that micro-changes in the outlines of forest areas do not significantly affect the results of the study, and the main processes of forest changes are sufficiently accurate and informative. Different data sources with different accuracy of data collection were used, but the results of the study will not be affected by a small difference in the accuracy of the data, since large areas of forests are studied. Description of data sources used:  
1. Old maps:  
(a) Topographic maps of the European part of the Empire of the 2 nd half of the 19 th century created by the Military Topography Department, edition of 1860-1915. Scale--3 miles are equal to 1 English inch, which corresponds to a scale of 1:126,000. The map page is rectangular, 58 \(\times\) 42 cm; it corresponds to an area of 73 \(\times\) 53 km at the location. During the maps' creation, the works in the military topographic photo were completed around 1845, the area was reconnoitred, and the data were updated in 1865 (mainly names of villages and settlements). (b) Maps of the Lithuanian Military Topography Department of the 1 st half of the 20 th century, 1933-1940 edition, scale 1:100,000. The maps map out the territory of the country of that time; the map sheet size is 47 \(\times\) 45 cm. They were created using available material (aerial photographs, other maps), without fieldwork. (c) Topographic maps of the 2 nd half of the 20 th century, scale 1:50,000, 1988 edition. Maps with a 1:50,000 scale were made after the updating of mapping data in 1956-1957. Aerial photos and area survey data were used for the update. 2. CORINE Land Cover database of 2018 (CHA18_LT) ([[https://www.geoportal.lt/geoportal/duomenu-paieska#queryText=corine](https://www.geoportal.lt/geoportal/duomenu-paieska#queryText=corine)]([https://www.geoportal.lt/geoportal/duomenu-paieska#queryText=corine](https://www.geoportal.lt/geoportal/duomenu-paieska#queryText=corine))). It was created by automatically merging databases CLC12_LT and CHA18_LT and interpreting the IRS satellite imagery of 2012-2013 and Sentinel-2 satellite imagery of 2017. The smallest mapped area object is 25 ha; the smallest mapped area object in the database of changes CHA18_LT is 5 ha (https://www. geoportal.lt/geoportal/duomenu-paieska#queryText=corine). This is a vector land cover dataset divided into 44 classes. There are 30 classes according to the type of land cover and purpose of use in the territory of Lithuania. The following covers (marked with codes) were used for the study: deciduous forests (311), coniferous forests (312), and mixed forests (313). During the study, these covers were treated as forest cover. 3. State forest cadastral data. The forest cadaster of the Republic of Lithuania collects data on all Lithuanian forests regardless of their ownership form and protection regime. The cadastral object is a forest land valuation plot. The vector dataset was downloaded from ([[https://www.geoportal.lt/geoportal/](https://www.geoportal.lt/geoportal/)]([https://www.geoportal.lt/geoportal/](https://www.geoportal.lt/geoportal/))); data on tree species, age, and land plot areas were used in the research. 4. Orthoph