Assessment of natural forest regeneration after fire using data obtained with UAV

Analysis of the success of reforestation after a fire is the most important task of forestry. For these purposes, in the summer of 2021, aerial photography was carried out from a Phantom 4 pro UAV (Unmanned Aerial Vehicle) of a 15-year-old burnt-out (2006) along the north-western border of the Botanical Garden of Petrozavodsk State University (Republic of Karelia). In addition to this, a full-scale survey was carried out at the registration sites. Before the forest fire, rocky Scots pine (Pinus sylvestris L.) trees grew. The work was carried out in order to assess the state of natural renewal after a fire along rocky outcrops by combining the processing of aerial photography data with field surveys. As a result of photogrammetric processing, an orthophotomap with a spatial resolution of 4.6 cm/pix, a height map and three-dimensional point clouds were reconstructed. To analyze the quantitative distribution of the territory according to the species composition, the trees were pinned on the orthophotomap according to the registration areas of field surveys, as a result of which the quantitative distribution of tree species was determined in the ratio of 64 % Scots pine and 23 % of drooping birch (Betula pendula Roth) (other species were not identified). Field surveys showed that after the fire, a viable young stand of mixed composition with a predominance of Scots pine (71% of the total number of tree species) was formed. In addition to Scots pine, drooping birch (22 %), aspen (Populus tremula L.) and gray alder (Alnus incana (L.) Moench) (3.5 % each) participate in the formation of young stands on this burned-out area. These indicators are consistent with the analysis of the orthomosaic of the area (the error is less than 10 %). When comparing the height of plants on three-dimensional clouds of points with field measurements, it was possible to reliably determine only the height of plants for a large generally accepted category (> 1.5 m). The maximum height of Scots pine trees in the study area is 6 m, and the average values varied from 3.5 to 4.5 m, which indicates the success of reforestation after burning on rocky outcrops.