The current state of forest stands has been assessed in the most polluted part of East Ural Radioactive Trace (EURT) formed as a result of the Kyshtym accident in 1957. The main radionuclide in this area is 90Sr, with soil contamination density varying from 70 to 67 450 kBq/m2. Birch grass forests dominate in this territory, and more than 85% of them are aged between 70 and 120 years. Pine forests are relatively rare, with tree age reaching 80–110 years in 58% of these stands. The average age of birch forests proved to decrease with an increase in the density of soil contamination with 90Sr, which was explained by the increasing proportion of young birch stands formed in the most contaminated areas 25–30 years after the accident. No significant dependence of relative forest density and timber stock on the level of soil contamination with 90Sr in different allotments was revealed. A comparison of timber stock recorded in 2003 and 2020 showed that this parameter was increasing more rapidly in the most contaminated plots due to active growth of young birch stands in these areas during the corresponding period. Assessing natural forest regeneration in the EURT area, it was found that tree regrowth is formed in most sites, which is potentially capable of ensuring further development of forest ecosystems. The emergence of pine regrowth was observed for the first time in plots closest to the epicenter of the accident, where all pine trees perished during the acute radiation period. These samples contained an increased proportion of plants with morphological abnormalities. No dependence of the rate of tree die-off on the soil contamination density with 90Sr was revealed. The assessment the loss of trees and natural regeneration of forests was difficult due to fires that occur regularly in the EURT area.

Общеизвестно, что каждое из трех последних десятилетий характеризовалось более высокой тем- пературой у поверхности Земли по сравнению с любым предыдущим десятилетием начиная с 1950 г. На фоне этих изменений в научной литературе в последнее время появляется все большее количество работ, свидетельствующих об экспансии древесных и кустарниковых видов в арктические и высокогор- ные экосистемы. В статье приведены результаты исследования формирования древостоев верхней гра- ницы леса и зарослей крупных кустарников в одном из малоизученных регионов центрального сектора Субарктики России – плато Путорана. Объектом исследования явились древостои лиственница Гмелина Larix gmelinii Rupr. и заросли ольхи кустарниковой Duschekia fruticosa (Rupr) Pouzar. Показано, что на фоне современных изменений климата в последнем столетии (особенно во второй половине) происхо- дило смещение верхней границы распространения древесной и кустарниковой растительности выше в горы. Доказательством данных процессов служит закономерное изменение морфометрических параметров и среднего возраста изучаемых видов по мере продвижения в гору в последнем столетии. It is well known that each of the last three decades has been characterized by a higher temperature at the Earth’s surface compared to any previous decade since 1950. Against the background of these changes, an increasing number of works have recently appeared in the scientifi c literature, indicating the expansion of tree and shrub species into Arctic and high-altitude ecosystems. The article presents the results of a study of the formation of stands of the upper border of the forest and thickets of large shrubs in one of the poorly studied regions of the central sector of the Subarctic of Russia – the Putorana plateau. The object of the study was stands of Gmelin larch (Larix gmelinii Rupr.) and thickets of shrub alder (Duschekia fruticosa (Rupr) Pouzar). It is shown that against the background of modern climate changes in the last century (especially in the second half), the upper limit of the distribution of woody and shrubby vegetation was shifted higher into the mountains. The proof of these processes is the regular change in morphometric parameters and the average age of the studied species as they move uphill in the last century.

Analysis of the age structure of Dahurian larch (Larix gmelinii Rupr.) forests in the western part of the Putorana Plateau (Sukhie Gory Range) and comparison of diachronous topographic maps and satellite images have revealed changes in the altitudinal position of the upper boundary of tree vegetation. The most significant changes occurred on south- and southwest-facing slopes. Correlations of trunk diameters with the phytomass of trees and its fractions have been found. The course of changes in the structure and phytomass of tree stands in the upper timberline over the past centuries has been reconstructed. Forest expansion has been facilitated by the general change in climate conditions (warming) in the study area.

Changes in the altitudinal position of the timberline in high mountain areas of the Nether-Polar Urals and basic factors that influence such changes have been revealed on the basis of comparison of the age structure of Siberian larch (Larix sibirica) and arctic birch (Betula tortuosa) tree stands and photographs made in different years. On the mountain slopes studied, an upward shift of the timberline took place in areas covered in winter with thick snow (in the late 18th century), with Siberian larch being the pioneer species. Larch began colonizing areas with a thin snow cover in the 20th century. Birch appeared later and has since strengthened its positions. The increase in winter temperatures and precipitation facilitated the expansion of the forest.