Changes in the structure of a stand on a drained oligotrophic swamp for 50 years on West Dvina peatland-forest station in Tver oblast

West Dvina peatland-forest station of the Institute of Forestry Sciences of the Russian Academy of Sciences is located in the sub-taiga of European Russia. Scientific tasks related to the biogeocoenological study of the nature of swampy forests and swamps are solved at the station. In the period during 1972–1973, forest reclamation works were carried out here. Permanent sample plots were laid on the drained areas, including one in 1974 on a forested oligotrophic swamp. In 2023, the research was carried out again. The purpose of the study was to evaluate changes in the structure of a forest stand on a forested oligotrophic swamp over 50 years after drainage. The objects of the study were the forest inventory data for the tree layer on permanent sample plots in 1974 and 2023. Sample plots were laid in the middle of the space between the drainage channels and near them. The study uses generally recognized field and laboratory inventory methods. Regression equations were constructed to accurately calculate certain indicators. For statistical analysis of the similarity between the diameters on the sample plots that do not obey the normal distribution, the nonparametric Mann-Whitney U test, recommended in such cases, was used. The development dynamics of the stands on the sample plots was studied by comparing the inventory indicators for 1974 and 2023. Due to the lack of control for the drained object in 2023, in order to identify the degree of drainage efficiency, tree height was calculated based on an algebraic model of stand growth based on the Mitcherlich function. Comparing the inventory indicators and the intensity of drainage of Pinetum andromedo-eriophoroso-sphagnosum over 50 years, it can be noted that in the process of drainage there was a change in forest types to Pinetum ledoso-sphagnosum turfosum, located in the middle of the inter-channel space and undergoing extensive drainage, and to Pinetum ledoso-hylocomioso-sphagnosum turfosum, located near the channel and being subjected to normal drainage. The yield class has improved from Vb to Va. The inventory indicators characterising the productivity of the stand have changed significantly over 50 years, including the wood stock of the stand that has increased 3.5 and 4.9 times in drained pine forests. The compared stands belong to the age class V, however, older trees died out in the drained stands. Statistical analysis showed minor but significant differences in diameters between normally drained and extensively drained pine forests. The effect of drainage showed there is a significant difference in the average heights in the drained pine forests (more than 36%) compared to the model height of the undrained pine forests. For 50 years after the drainage of oligotrophic pine forests, a certain effect of their drainage can be observed. However, the overall impact of such drainage on forest management is low.