Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE

This study was funded by the WSL-internal COSMIC project (5233.00148.001.01), the ETHZ (Laboratory of Ion Beam Physics), the Swiss National Science Foundation (SNF Grant 200021L_157187/1), and as the Czech Republic Grant Agency project no. 17-22102s.Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.Publisher PDFPeer reviewe

Arctic Greening Caused by Warming Contributes to Compositional Changes of Mycobiota at the Polar Urals

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

Climate change evidence in tree growth and stand productivity at the upper treeline ecotone in the Polar Ural Mountains

Abstract 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

Climate regimes override micro-site effects on the summer temperature signal of Scots pine at its northern distribution limits

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Types of Ecological Upper Tree Lines at Dalniy Taganai Mountain in the Southern Urals

На примере горы Дальний Таганай (хр. Таганай, Южный Урал) проведено выделение типов верхних границ леса на основе ведущего экологического фактора, влияющего на морфометрические характеристики ели сибирской (Picea obovata Ledeb.). Крутизна склонов и экспозиция оказывают влияние на распределение экологических факторов (солнечной радиации, осадков и ветра), что в свою очередь ведет к изменению условий произрастания и формированию разных экологических типов верхних границ леса. Следовательно, температура – основной, но не единственный фактор, влияющий на динамику верхней границы леса. Выделено четыре типа границ: термическая, курумная, ветровая и снеговая. На каждой границе дано детальное описание растительного покрова. Показаны различия между границами по геофизическим и топографическим характеристикам склонов, растительному покрову, морфометрическим характеристикам деревьев и их годичному приросту. Наиболее протяженной оказалась курумная граница, наименее протяженной – снеговаяTemperature is not the only driver of the upper tree line dynamics in mountain settings. In recent years, researchers have focused on the study of the spatiotemporal dynamics of forest stands under temperature-limiting conditions (at the thermal tree line). The preliminary results of differentiation of ecological types of the upper tree lines of the Siberian spruce (Picea obovata Ledeb.) at Dalniy Taganay Mountain in the Southern Urals are presented. Steepness of slopes and exposure influence the distribution of environmental factors (solar radiation, precipitation and wind) which change growth conditions and form different ecological types of the upper tree line. Four main ecological drivers were noted and four types of tree line were proposed: the thermal, wind, snow and edaphic tree lines. A detailed description of the vegetation cover was done. The revealed types of tree lines are distinguished distinctly based on geomorphologic and topographical features of every study site, the type of the vegetation cover, morphometric characteristics of trees and their annual growth. The edaphic tree line is the longest and the snow tree line is the shortest one. Further studies are needed to more precisely determine the tree line driver

Types of Ecological Upper Tree Lines at Dalniy Taganai Mountain in the Southern Urals

На примере горы Дальний Таганай (хр. Таганай, Южный Урал) проведено выделение типов верхних границ леса на основе ведущего экологического фактора, влияющего на морфометрические характеристики ели сибирской (Picea obovata Ledeb.). Крутизна склонов и экспозиция оказывают влияние на распределение экологических факторов (солнечной радиации, осадков и ветра), что в свою очередь ведет к изменению условий произрастания и формированию разных экологических типов верхних границ леса. Следовательно, температура – основной, но не единственный фактор, влияющий на динамику верхней границы леса. Выделено четыре типа границ: термическая, курумная, ветровая и снеговая. На каждой границе дано детальное описание растительного покрова. Показаны различия между границами по геофизическим и топографическим характеристикам склонов, растительному покрову, морфометрическим характеристикам деревьев и их годичному приросту. Наиболее протяженной оказалась курумная граница, наименее протяженной – снеговаяTemperature is not the only driver of the upper tree line dynamics in mountain settings. In recent years, researchers have focused on the study of the spatiotemporal dynamics of forest stands under temperature-limiting conditions (at the thermal tree line). The preliminary results of differentiation of ecological types of the upper tree lines of the Siberian spruce (Picea obovata Ledeb.) at Dalniy Taganay Mountain in the Southern Urals are presented. Steepness of slopes and exposure influence the distribution of environmental factors (solar radiation, precipitation and wind) which change growth conditions and form different ecological types of the upper tree line. Four main ecological drivers were noted and four types of tree line were proposed: the thermal, wind, snow and edaphic tree lines. A detailed description of the vegetation cover was done. The revealed types of tree lines are distinguished distinctly based on geomorphologic and topographical features of every study site, the type of the vegetation cover, morphometric characteristics of trees and their annual growth. The edaphic tree line is the longest and the snow tree line is the shortest one. Further studies are needed to more precisely determine the tree line driver

Excursions in the 14C record at AD 774-775 from tree rings from Russia and America

he calibration of radiocarbon dates by means of a master calibration curve has been invaluable to Earth, environmental and archeological sciences, but the fundamental reason for calibration is that atmospheric radiocarbon content varies because of changes in upper atmosphere production and global carbon cycling. Improved instrumentation has contributed to high-resolution (interannual) radiocarbon activity measurements, which have revealed sudden and anomalous activity shifts previously not observed at the common resolution of 5–10 years of most of the calibration scale. One such spike has been recently reported from tree rings from Japan and then again in Europe at A.D. 774–775, for which we report here our efforts to both replicate its existence and determine its spatial extent using tree rings from larch at high latitude (northern Siberia) and bristlecone pine from lower latitude (the White Mountains of California). Our results confirm an abrupt ~ 15‰ 14C activity increase from A.D. 774 to 776, the size and now the hemispheric extent of which suggest that an extraterrestrial influence on radiocarbon production is most likely responsible.6 month embargo; published online: 25 April 2014This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Modern Dynamics of High-Mountain Forests in the Northern Urals: Major Trends

На фоне наблюдаемого потепления климата во многих регионах отмечается смещение верхней и полярной границ распространения древесной растительности, изменение структуры и состава древостоев. Особый интерес вызывают регионы, растительность которых не испытывала масштабных антропогенных воздействий, что позволяет оценить естественную динамику древостоев. Данная работа посвящена изучению возрастной и морфологической структуры древесного яруса смешанных редколесий и лесов на восточном отроге хребта Молебный Камень (Северный Урал). В основу исследования положены методы пробных площадей и древесно-кольцевого анализа. В экотоне верхней границы древесной растительности отмечены существенные изменения состава, морфологической и возрастной структуры древостоев, произошедшие на фоне повышения летних температур и увеличения количества зимних осадков, наблюдаемых в данном районе со второй половины ХХ в. Анализ климатического отклика, содержащегося в четырех обобщенных древесно-кольцевых хронологиях, построенных по лиственнице сибирской, сосне сибирской, пихте сибирской и ели сибирской, показал, что на радиальный прирост изученных деревьев наибольшее влияние оказывают весенние и раннелетние условия произрастания. Полученные данные могут быть использованы при проведении лесохозяйственных и лесоустроительных работIn many regions climate warming has caused shifts of the upper and polar boundaries of woody vegetation and changes in the structure and composition of tree stands. Regions whose vegetation has not experienced large-scale anthropogenic impacts have attracted particular interest of researchers assessing the natural dynamics of stands. This work is devoted to the study of the age and morphological structure of the tree layer of mixed woodlands and forests on the Eastern spur of the Molebny Kamen’ ridge (Northern Urals). The study is based on the quadrat sampling method and tree-ring analysis. The tree-line ecotone shows significant changes in the composition and morphological and age structure of forest stands that have occurred in this region since the mid-twentieth century, with the rising summer temperatures and increasing winter precipitation. Climatic response analysis, contained in 4 generalized tree-ring chronologies constructed for the Siberian larch, Siberian pine, Siberian fir and Siberian spruce, suggests that radial growth of the trees is mostly influenced by spring and early summer growing conditions. The results of the study can be used in forestry and forest management activitie