ИСТИНА

Contemporary climate changes are several times more intense in the Arctic than the global average. That is reflected in the rapid change in natural conditions at high latitudes. Vegetation is both a sensitive indicator of changes in external impacts and a factor that determines the conditions of heat exchange between the atmosphere and underlying rocks. Ground covers are as powerful regulator of permafrost conditions as climate change. The observed climate warming leads to a noticeable restructuring of typical and mountain tundra landscapes which occupy vast areas of northeast Russia. The evolution of vegetation manifests on a scale of decades and can provoke both positive and negative feedbacks, which affects in its order the parameters of the seasonally thawed (active) layer of the soils and the state of permafrost. This study is an analysis of long-term trends in climate change compared with the dynamics of seasonal soil thawing depth and changes in vegetation composition within two key monitoring sites included in the Circumpolar Active Layer Monitoring program (CALM) – R27 Lavrentiya and R41 Lorino. The sites are located in the typical tundra landscapes of the coastal plains of the Chukotka Peninsula (Chukchi Autonomous Okrug, NE Russia). They are squares with an area of 1 hectare and a grid of nodes located every 10 meters (121 nodes in total). Monitoring of seasonal soil thawing was carried out with the method of mechanical soil probing at the peak of maximum development of the active layer (August-September) during 2000 to 2024 period. Vegetation cover was studied by field methods for the period from 2013 to 2024. The projective cover of vegetation was determined at each of the 121 grid points at the peak of the growing season (late July, early August) for the main species, including mosses and lichens (13 species in total). Climatic variations were determined for the period from 2000 to 2024 based on data from the nearest weather station in the community of Uelen. Regional climate changes were determined using NCEP/NCAR reanalysis data. Changes in background vegetation around the monitoring sites were determined within the key polygon (172 km2) with the NDVI index, which was calculated for each peak of the growing season from 2000 to 2024. The obtained results show that at the background of a rapid increase in air temperature (0.72°C/decade), the thickness of the active layer had been growing at a rate of 0.5-1.5 cm/year. Changes in permafrost-climatic conditions in the northeast of Russia led to changes in vegetation cover, which mainly affected species that are indicators of insufficient or excessive moisture.