Shrubs are expanding rapidly in response to climate warming, yet their dendroclimatic responses remain poorly characterised in the Russian Arctic compared to other circumpolar regions. We analysed the radial growth responses of green alder (Alnus alnobetula subsp. fruticosa Raus) to climate variables across two adjacent Arctic regions: the southern Yamal Peninsula and Polar Urals. Tree-ring width chronologies were developed from 68 individual shrubs sampled between 1997 and 2024, yielding the longest continuous global alder chronology (154 years, 1869–2023). Correlation analysis revealed that June-July temperatures were the primary driver of radial growth across all sites (p < 0.01), consistent with temperature-limited growth in high-latitude ecosystems. However, climate-growth relationships exhibited significant temporal and spatial heterogeneity. Precipitation signals were spatially heterogeneous, with April snowpack and July moisture limiting growth at specific sites. Daily response analysis revealed a critical 11–19-day advancement in peak growth correlation in the modern period (1974–2023) compared to earlier intervals, providing robust dendrochronological evidence of recent phenological shifts. These phenological shifts have significant implications for the trophic mismatch between vegetation productivity and reindeer calving timing, potentially threatening food security for indigenous herding communities. Our findings underscore the necessity of integrating shrub dendrochronology into Arctic climate reconstructions and highlight the complex nature of climate-vegetation relationships under rapid warming.

Current climate models project an increased frequency and intensity of droughts in the Eurasian forest-steppe. Although forests in this area are at risk from increasing aridization, our understanding of the forest vegetation response to increasing drought stress remains limited. Here, we examined a network of 12 new tree-ring width (TRW) chronologies of Scots pine (Pinus sylvestris L.) in the forest-steppe zone of Western Siberia to determine the effects of climate variability on tree radial growth. The data were generalized using principal component analysis (PCA) into three regional chronologies characterized by a diverse climatic signal. While the northern sites demonstrated a weak growth–climate response, TRW at the southern sites strongly correlated with the six-month standardized precipitation evapotranspiration index (SPEI6) in February–July (r = 0.65, p < 0.001). Based on this relationship, we defined the years with the extremely low summer SPEI6 (July) in the southern forest-steppe of Western Siberia for the period from 1850 to 2020. Our reconstruction identified the most severe droughts during the last two centuries in 1851, 1890, 1904, 1911, 1931, 1952, 1975–1977, 1989, 2004, 2010, and 2012. These results indicate the increasing effect of drought stress on Scots pine populations along the aridity gradient in the forest-steppe ecotone, emphasizing the potential vulnerability of trees under changing climate.

Dendrochronological methods have confidently entered the practice of history and archeology. Dendroarcheological studies on the European territory of Russia and in Siberia have led to results that were previously unavailable or did not provide high accuracy in determining the dates of the appearance of historical and archaeological objects. Collaboration between archaeologists and dendrochronologists sometimes gives unique research results. At present, the region of the Southern Urals and the Trans-Urals remains "in the shadow" of such studies. This publication evaluates the possibilities of using the historical and archaeological timber of the Southern Urals and the Trans-Urals to build longterm tree-ring chronologies, which will become a tool for interdisciplinary studies. Such chronologies will make it possible to accurately date wood artifacts as well as to carry out regional reconstructions of weather and climate conditions. Currently, our collection of historical timber consists of more than 350 cross-sections and several dozen cores of Scots pine and Siberian larch. The dating of historical timber is based on the longest (up to 250 years) chronologies of living pine and larch trees. The duration of the chronology is 478 years. Dates of construction of some historical buildings have been obtained. The oldest is the house in the village Krestovka, Dalmatovsky district, Kurgan region. It was built in 1816 and remained residential until the 1980s. All chronologies are well dated and contain a strong and time-stable climate signal. This means that chronologies can be used to develop reconstructions of weather-climate conditions-air temperature, precipitation, and the Palmer Drought Severity Index (scPDSI). An analysis of the collected historical timber from the Southern Urals and the Trans-Urals regions showed that there is a prospect of building chronologies span 700 years and the use of timber from archaeological excavations will help extend them up to 1000 years. Also, archaeological wood should be used to build "floating" chronologies", which will allow to prolong the extension of absolute continuous chronologies.

The spatial and temporal dynamics of forest-tundra communities was studied on the Yamal Peninsula within the northern treeline ecotone. The paper presents the results of surveying 12 sample plots and more than 1000 trees of Siberian larch and Siberian spruce. Based on cross-dated tree-ring chronologies, the age structure and dynamics of stands for the last 150 years were obtained. Dynamic processes in stands of the northern treeline ecotone are most pronounced in the sparse forests, where there has been a sharp increase in stand density since the middle of the 20th century. Correlation analysis of tree establishment time with instrumental observations of climatic variables showed that the establishment of new larch and spruce individuals in different stand types is significantly influenced by the amount of precipitation in June-August.

On 12 sample plots established in the ecotone of the northern forest boundary in the Khadyta-Yakha River valley on the Yamal Peninsula, time of emergence and death, as well as productivity of about 1000 Siberian larch (Larix sibirica Ledeb.) and Siberian spruce (Picea obovata Ledeb.) trees were analyzed. Over the last 140 years, there has been a sharp increase in the stocks and annual growth of stem phytomass of woody plants within the studied ecotone. Since the 1970s, the average annual growth of phytomass has been increased by 1.2–39 times, which was facilitated by a 0.9°C increase in average June–July air temperature. However, this effect is insignificant in areas of mixed open forests subjected to periodic logging.

A climatic signal associated with the tree-ring width and the optical density of the wood (Blue Intensity) has been evaluated in two related pine species, European black pine ( Pinus nigra Arnold) and Turkish pine ( Pinus brutia Ten), growing on the southern coast of the Crimean Peninsula. The influence of the cumulative effect of moisture deficiency on the radial growth and lignification processes in the latewood of the studied species has been shown. The specific reaction of P. nigra growing in mountain areas to a long-term drought has been revealed. The prospect for use of the Blue Intensity index for dendroclimatic studies on the territory of the Crimean Peninsula has been demonstrated.

Climate change is most evident on the periphery of species distribution ranges. Using four tree-ring chronologies, we identified the most important climatic factors influencing the radial growth of black pine growing along an altitudinal gradient on the eastern slope of Mount Ai-Petri (Crimean Peninsula), at the northernmost part of its range. The relationship between tree-ring widths and climate was determined using response function analysis. Results from transects moving up the slope demonstrated an increase in the correlation between radial growth and the hydrothermal coefficient: from an almost complete absence of any correlation at the lowest elevation to 0.6 at the top. Furthermore, this variation in response was not only caused by differences in climatic variables, but also changed with topography, soil, and bedrock features. The ongoing climate aridization, now typically observed in the region, may lead to a decrease in the stability and persistence of black pine stands, especially in the upper part of the slope.

Climate change is most evident on the periphery of species distribution ranges. Using four tree-ring chronologies, we identified the most important climatic factors influencing the radial growth of black pine growing along an elevational transect on the eastern slope of Mount Ai-Petri (Crimean Peninsula), at the northernmost part of its range. The relationship between tree-ring width and climate was determined using response function analysis. Results indicate an increase in correlation between radial growth and hydrothermal data along the transect: from a near absence of any correlation at the lowest elevation to r = 0.6 at the top. This change in response was not only caused by differences in climatic variables, but also related to topography, soil, and bedrock features. The currently ongoing aridization may lead to a decrease in the stability and persistence of black pine stands only in the upper parts of Mount Ai-Petri.

Eleven stands of Scots pine (Pinus sylvestris L.) from the city of Ekaterinburg and its surroundings were sampled and analyzed using dendrochronological methods to detect the effects of climate, biotic and anthropogenic factors on the annual growth of trees. Tree-ring chronologies were developed for six sites within the city and for five control sites. All chronologies were highly and positively correlated before the 1940s. However, after this period, there was a significant decrease in the correlation among chronologies from urban and rural sites. Divergence lasted about 20 years. This firstly has an anthropogenic cause, mainly due to the evacuation in 1941 of more than 60 industrial factories to Sverdlovsk (now Ekaterinburg), which generated a significant increase in air pollution. Environmental pollution seems to negatively affect tree growth. In the early 1950s, trees in the region also suffered from severe droughts. The results of climate and historical data analysis suggest that the trees on urban sites were weakened by both climate and air pollution factors, which led to a massive nun moth (Lymantria monacha L.) infestation of trees. Defoliation led to a drastic reduction in tree-ring width and, in some cases, to the complete loss of annual rings. The recovery period lasted 10–15 years on average. Rural populations were much less affected by the insect outbreak. After urban populations of pine recovered in the 1960s, radial growth of urban and rural populations became synchronized again.

The study presents results of the influence of recreational impact on the radial growth of Scots pine (Pinus sylvestris L.) in old-growth stands at the sites with the V stage of recreational degradation on the territory of organized and unorganized recreation and undisturbed areas. Over the 100 years, no negative recreation-driven changes in the radial growth were found. There is a significant increase in the tree-ring width and the number of absent rings in the chronologies from active recreation sites. A linear relationship was found between the number of absent rings and Palmer's drought severity index. Under summer drought conditions, lake proximity may mitigate the negative effects of recreation on stands even at sites with V stage of recreational degradation.

Climate change effects are strongest in forest ecosystems at the limit of their distributions. Despite the evidence that treelines have shifted upwards by hundreds of meters, knowledge of the associated changes in the stand biomass is limited. In this study, stand biomass and changes to it during the last centuries were estimated along 20 altitudinal transects reaching from the historical (located in the 1950s–1960s) closed forest line up to the current treelines on mountain slopes of three subarctic regions of Russia (Kola Peninsula, Polar Urals, and Putorana Plateau) along a 2200 km long longitudinal gradient. The estimates were based on allometric measurements of 139 trees of five species (Betula pubescens Ehrh. ssp. tortuosa, Pinus sylvestris L., Picea abies Ledeb. ssp. obovata, Larix sibirica Ledeb., and Larix gmelinii Rupr.), stand structure assessments, and the demographic patterns of 9300 trees. During the 20th century, the growth and establishment of trees at the forest–mountain tundra transition (340–500 m width) increased exponentially. Since 1910 forest expansion and densification led to an accumulation of 621–748 tons of aboveground stand biomass per km of treeline length. The accumulation was two times higher below than above the contemporary closed forest line. Data analysis of weather stations showed that the 20th century’s climate had changed in a similar manner in the three study regions, namely vegetation periods became longer (8–10 days) and warmer (0.6–0.9 °C) and more snow fell in the cold period (+10–30%). Our results indicate that regional patterns in stand biomass at the treeline ecotone are primarily related to tree species composition as determined by macroclimatic conditions (e.g., continentality, sunshine hours), snowpack depth, and growing season duration. However, the stand biomass accumulation was driven by increases of early summer temperatures and early winter precipitation during the last century.

It has recently become a matter of discussion whether it is correct to use regional tree-ring chronologies in spatiotemporal climate reconstructions, since natural and climatic conditions in the regions may be heterogeneous, varying on different scales (from micro to global). We have studied the response of tree-ring width to climate in Scots pine (Pinus sylvestris L.) growing in the steppe zone, in insular pine forest of the Southern Urals and ribbon pine forests of Altai. Regional features and differences between the corresponding tree-ring chronologies obtained in the season of tree-ring formation (May–July) and spatiotemporal asynchrony in the long-term dynamics of tree-ring width in the study regions have been revealed.

Anna A. Oleshkevich, Specific features of change in enzymate activity in

The East Ural Radioactive Trace (EURT) resulted from the explosion at the Mayak Production Association in September 1957 (the Kyshtym accident). The majority of the Scots pine stands near the epicenter of the accident died in 1958–1959. Currently, we have found several small pine-birch stands with pine trees that are over 70 years old. Cores (96 samples) were analyzed employing dendrochronological methods to detect the effects of climate and ionizing radiation on the annual growth of trees. Tree-ring chronologies were developed for two control and three impact sites with different levels of radioactive contamination. In the first years after the accident, acute radiation exposure significantly reduced radial growth in trees in two contaminated sites, where initial contamination levels of 90Sr measured 3.7–26.6 MBq m−2; synchrony of the chronologies from the contaminated and control sites were disturbed. In the subsequent period, all chronologies have been highly synchronous. The Scots pine has revealed decreasing radial growth due to limitations in the amount of available moisture. The results suggest that both climate and ionizing radiation have limited the radial growth of pine trees. The effect of acute radiation contamination on the radial growth of trees was comparable to the effect of droughts – the main extreme climatic event in this region.

Aim To quantify tree biomass and stand productivity of treeline ecotones and identify driving factors. Location treeline ecotones of seven regions from the South to Polar Urals, spanning a latitudinal gradient of 1,500 km. Taxa Picea obovata, Betula pubescens, Larix sibirica. Methods Stand biomass and productivity were estimated across 18 elevational transects from the tree species line to the closed forest line based on allometric measurements of 326 trees (including roots for 53 trees), stand structure assessments and demographic patterns of 20,600 trees. Stand growth data were linked to (a) temperatures monitored in situ for five years in the South and Polar Urals, (b) climate variables extrapolated from nearby climate stations and (c) measures of nutrient availability in soils and tree foliage. Results treeline position along the latitudinal gradient occurred at a similar mean growing season temperature. Despite the common cold limitation of tree distribution along the Ural mountain range, stand biomass and productivity within the treeline ecotone decreased by a factor of three and five from the South to the Polar Urals, mainly due to a declining stand density. Among climatic variables, growing season length decreased by 20% and winter temperatures declined by 4 degrees C towards the Polar Urals, whereas growing degree days > 5 degrees C remained similar, averaging 554 +/- 9 degrees C. Soil development was poorer in the Polar than in the South Urals, and plant-available N and P in the soil were 20 and 30 times lower, respectively, probably due to lower winter temperatures. Main conclusions Our results suggest that once the thermal limitation for tree growth is relieved, soil fertility-restricted by permafrost and low soil temperatures during winter-plays a key and yet underexplored role for stand productivity in treeline ecotones. The observed latitudinal decline in stand productivity is important for above- and belowground diversity and functioning.

Background:Recent warming is affecting species composition and species areal distribution of many regions.However, although most treeline studies have estimated the rates of forest expansion into tundra, still little is known about the long-term dynamic of stand productivity at the forest-tundra intersection. Here, we make use of tree-ring data from 350 larch (Larix sibirica Ledeb.) and spruce (Picea obovata Ledeb.) sampled along the singular altitudinal treeline ecotone at the Polar Urals to assess the dynamic of stand establishment and productivity, and link the results with meteorological observations to identify the main environmental drivers. Results:The analysis of stand instalment indicated that more than 90％of the living trees appeared after 1900. During this period, the stand became denser and moved 50 m upward, while in recent decades the trees of both species grew faster. The maximum afforestation occurred in the last decades of the twentieth century, and the large number of encountered saplings indicates that the forest is still expanding. The upward shift coincided with a slight increase of May–August and nearly doubling of September–April precipitation while the increase in growth matched with an early growth season warming (June+0.27 °C per decade since 1901). This increase in radial growth combined with the stand densification led to a 6–90 times increase of biomass since 1950. Conclusion:Tree-ring based twentieth century reconstruction at the treeline ecotone shows an ongoing forest densification and expansion accompanied by an increased growth. These changes are driven by climate change mechanism, whereby the leading factors are the significant increase in May–June temperatures and precipitation during the dormant period. Exploring of phytomass accumulation mechanisms within treeline ecotone is valuable for improving our understanding of carbon dynamics and the overall climate balance in current treeline ecosystems and for predicting how these will be altered by global change.

Pinus brutia var. pityusa (Steven) Silba (Calabrian pine) is considered a vulnerable species because of reductions in its population sizes linked to habitat decline in recent decades. Global warming alongside the collateral modification of precipitation regimes may markedly affect the distribution ranges of this species. In this dendroecological study, we identified the most influential climatic factors affecting the radial growth of P. brutia on the norther n and easter n coasts of the Black Sea among the norther n refugia of this species. Chronologies from five sites located on the Crimea Peninsula and the Caucasian coast and exposed to varying climatic conditions were used in this analysis. The study of environmental factors controlling the growth ofP. brutia trees in the coastal populations of Crimea and the Caucasus revealed that within the longitudinal transect, which encompasses a specific range of climatic conditions, correlations between climate and the growth of P. brutia under analogous orographic conditions are similar. Aridisation of the dry Crimean climate in 1981-2012 led to an increase in the tree growth response. In the same period, populations ofP. brutia trees growing in the subtropical climate of the Black Sea coast exhibited a weakened growth response to the point of disappearance. The norther n populations of P. brutia, which are at the climatic limit of the species' distribution, are exposed to a high risk of increasing climate aridisation. Ou r findings could provide use f u l information for further research on the effects of climate change on Black Sea coastal forest ecosystems.

Aboveground species richness patterns of vascular plants, aphyllophoroid macrofungi, bryophytes and lichens were compared along an altitudinal gradient (80–310 m a.s.l.) on the Slantsevaya mountain at the eastern macroslope of the Polar Urals (Russia). Five altitudinal levels were included in the study: (1) Northern boreal forest with larch-spruce in the Sob’ river valley habitats; (2–3) two levels of closed, northern boreal, larch-dominated forests on the slopes; (4) crook-stemmed forest; (5) tundra habitats above the timberline. Vascular plant or bryophyte species richness was not affected by altitudinal levels, but lichen species richness significantly increased from the river valley to the tundra. For aphyllophoroid macrofungi, species richness was highest at intermediate and low altitudes, and poorest in the tundra. These results indicate a positive ecotone effect on aphyllophoroid fungal species richness. The species richness of aphyllophoroid fungi as a whole was neither correlated to mortmass stocks, nor to species richness of vascular plants, but individual ecological or morphological groups depended on these parameters. Poroid fungal species richness was positively correlated to tree age, wood biomass and crown density, and therefore peaked in the middle of the slope and at the foot of the mountain. In contrast, clavarioid fungal species richness was negatively related to woody bio- and mortmass, and therefore peaked in the tundra. This altitudinal level was characterized by high biomass proportions of lichens and mosses, and by high litter mortmass. The proportion of corticoid fungi increased with altitude, reaching its maximum at the timberline. Results from the different methods used in this work were concordant, and showed significant patterns. Tundra communities differ significantly from the forest communities, as is also confirmed by nonmetric multidimensional scaling (NMDS) analyses based on the spectrum of morphological and ecological groups of aphyllophoroid fungi.

The long-term influence of climate change on spatio-temporal dynamics of the Polar mycobiota was analyzed on the eastern macro slope of the Polar Urals (Sob River valley and Mountain Slantsevaya) over a period of 60 years. The anthropogenic impact is minimal in the study area. Effects of environmental warming were addressed as changes in treeline and forest communities (greening of the vegetation). With warming, permafrost is beginning to thaw, and as it thaws, it decomposes. Therefore, we also included depth of soil thawing and litter decomposition in our study. Particular attention was paid to the reaction of aphyllophoroid fungal communities concerning these factors. Our results provide evidence for drastic changes in the mycobiota due to global warming. Fungal community composition followed changes of the vegetation, which was transforming from forest-tundra to northern boreal type forests during the last 60 years. Key fungal groups of the ongoing borealization and important indicator species are discussed. Increased economic activity in the area may lead to deforestation, destruction of swamps, and meadows. However, this special environment provides important services such as carbon sequestration, soil formation, protecting against flood risks, and filtering of air. In this regard, we propose to include the studied territory in the Polarnouralsky Natural Park.