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Responding to a discrepancy between dendro-reconstruction and climate model during large volcano eruptions, scientists have been debating a missing tree ring (MTR) hypothesis—trees missing an annual ring at a large scale due to extreme cooling. Although both parties claim victory, their arguments are shown to be compromised in our analysis. On the one hand, one party’s argument based on the rarity of missing rings in current data cannot serve as evidence against the MTR because data collection methods already assume the MTR to be impossible; on the other, the other party’s hypothesis testing cannot support the MTR because it merely shows that data in volcanic years are less certain, which is known. Lastly, our analysis highlights a current knowledge gap in tree growth in extreme conditions and thus we urge scientists to perform natural and interventional experiments to understand tree growth limitations. Filling this gap will enhance dendro-reconstructions. [ABSTRACT FROM AUTHOR]

The process-based xylem formation model is an important tool for understanding the radial growth process of trees and its influencing factors. While numerous xylogenesis models for conifers have been developed, there is a lack of models available for non-coniferous trees. In this study, we present a process-based model designed for xylem formation and ring growth in broad-leaved trees, which we call the Broad-leaved Tree-Ring (BTR) model. Climate factors, including daylength, air temperature, soil moisture and vapor pressure deficit, drive daily xylem cell production (fibers and vessels) and growth (enlargement, wall deposition). The model calculates the total cell area in the simulated zone to determine the annual ring width. The results demonstrate that the BTR model can basically simulate inter-annual variation in ring width and intra-annual changes in vessel and fiber cell formation in Fraxinus mandshurica (ring-porous) and Betula platyphylla (diffuse-porous). The BTR model is a potential tool for understanding how different trees form wood and how climate change influences this process., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Intra-annual variations of carbon stable isotope ratios (δ13C) in different tree compartments could represent valuable indicators of plant carbon source-sink dynamics, at weekly time scale. Despite this significance, the absence of a methodological framework for tracking δ13C values in tree rings persists due to the complexity of tree ring development. To fulfill this knowledge gap, we developed a method to monitor weekly variability of δ13C in the cambium-xylem continuum of black spruce species [Picea mariana (Mill.) BSP.] during the growing season. We collected and isolated the weekly incremental growth of the cambial region and the developing tree ring from five mature spruce trees over three consecutive growing seasons (2019-2021) in Simoncouche and two growing seasons (2020-2021) in Bernatchez, both located in the boreal forest of Quebec, Canada. Our method allowed for the creation of intra-annual δ13C series for both the growing cambium (δ13Ccam) and developing xylem cellulose (δ13Cxc) in these two sites. Strong positive correlations were observed between δ13Ccam and δ13Cxc series in almost all study years. These findings suggest that a constant supply of fresh assimilates to the cambium-xylem continuum may be the dominant process feeding secondary growth in the two study sites. On the other hand, rates of carbon isotopic fractionation appeared to be poorly affected by climate variability, at an inter- weekly time scale. Hence, increasing δ13Ccam and δ13Cxc trends highlighted here possibly indicate shifts in carbon allocation strategies, likely fostering frost resistance and reducing water uptake in the late growth season. Additionally, these trends may be related to the black spruce trees' responses to the seasonal decrease in photosynthetically active radiation. Our findings provide new insights into the seasonal carbon dynamics and growth constraints of black spruce in boreal forest ecosystems, offering a novel methodological approach for studying carbon allocation at fine temporal scales., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Independent identification of carbon emission peaks determined from fuel inventories is a challenging goal. Because of the complete depletion of radiocarbon ( 14 C) in fossil fuel sources, the measurement of atmospheric 14 CO 2 has proven to offer a means of achieving this goal. Here, we present a study identifying peak carbon emissions from two Chinese cities using urban tree-ring Δ 14 C time series during 2000-2019. After subtracting background atmospheric Δ 14 C from urban tree-ring Δ 14 C to isolate local Δ 14 C (Δ 14 C local ), we find a minimum in 2010 (-51.1 ± 4.5‰) in Beijing and in 2013 in Xi'an (-52.5 ± 0.5‰). These levels correspond to an urban carbon emission peak in 2010 and in 2013 in the two respective cities. The urban carbon emission peaks are further identified by the declines of the mean absolute interannual rate of decrease of tree-ring Δ 14 C during a period, with the respective values of 3.6 and 6.4 ‰/yr after and before a turning point in Beijing and 3.0 and 6.0 ‰/yr after and before a turning point in Xi'an. This study provides an observation method to identify carbon emission peaks in basin cities.

Tree-ring data are pivotal for decoding the age and growth patterns of trees, reflecting the impact of environmental factors over time. Addressing the significant shortcomings of traditional, labour-intensive and resource-demanding methods, we propose an innovative automated technique that utilizes panchromatic images and deep learning for measuring tree rings. The method utilizes convolutional neural networks to enhance image quality, precisely delineate tree rings through segmentation and perform ring counting and width calculation in the post-processing stage. We compiled an extensive data set from diverse sources, including Beijing Forestry University and the Summer Palace, to train our algorithm. The performance of our method was validated empirically, demonstrating its potential to transform tree-ring analysis and provide deeper insights into ecological and climatological research., (© 2024 John Wiley & Sons Ltd.)

Since the 1990s, global warming has substantially affected the dynamic responses of forest ecosystems to drought by altering tree growth and ecosystems carbon cycling. The Loess Plateau is a typical vegetation recovery region with an arid and semiarid climate. However, the responses of the vegetation in this region to drought have not been fully studied. We therefore aimed to characterize these responses in tree-ring samples, which were obtained by drilling tree cores with a growth cone, for establishing the tree-ring width chronologies. In addition, we investigated the main factors controlling the radial growth of Chinese pine (Pinus tabulaeformis) and its dynamic responses to drought in the Loess Plateau using correlation analysis. Our results show that radial growth in Chinese pine had a positive correlation with precipitation during the last growing season, pre-growing season, and entire current growing season. The correlation between the radial growth and temperature was inconsistent between different sampling sites and time periods. These suggest that precipitation was more likely to affect radial vegetation growth than temperature. Moreover, the drought indices calculated using data before the year 2000 more accurately reflected the vegetation drought situation in Loess Plateau than data from the last 20 years. The drier the place, the more accurately the drought indices represented the responses of vegetation to drought. However, these indices cannot satisfactorily capture the drought responses of vegetation in wet regions. Furthermore, the PDSI was more accurate than the SPEI at capturing the effects of drought on radial vegetation growth. Understanding the response mechanism of the radial growth of Chinese pine to drought can provide theoretical support for ecological protection, forest management, and ecological construction under climate change.

Tree-ring width (TRW), stable carbon isotope ratio (δ13C) and intrinsic water use efficiency (iWUE) data set chronologies were built for the period 1961–2000 for two oak species (pedunculate oak – Quercus robur L. and Turkey oak – Quercus cerris L.) in northwestern Serbia (Vojvodina province). We focused on the response of the two oak species to measured meteorological data (temperature, precipitation and cloud cover), drought events expressed by six meteorological drought indices, and river water level to better understand their drought tolerance and stress and to assess the reliability of the species response to climate and drought indices when using TRW or δ13C. Turkey oak exhibited better drought tolerance (and less drought stress) compared to pedunculate oak, as manifested, respectively, by less negative δ13C and lower iWUE values. Based on a generalised additive mixed model (GAMM) among the six drought indices studied, the standardised precipitation evapotranspiration index and the standardised precipitation index showed the best fit with both TRW and δ13C, while the Palmer drought severity index exerted a strong influence only on TRW. It was thus concluded that δ13C responds more strongly and rapidly to climate variations than TRW.

The tree-ring fire scar stands as a pivotal proxy for reconstructing historical wildfire occurrences, providing invaluable context for comprehending contemporary wildfire activities during the Anthropocene era. Precise identification of fire scars often necessitates sampling complete tree disks. Yet, stringent forest resource protection policies limit such collection in certain regions, thus curtailing the application of tree-ring-based fire reconstruction. While current methods based on tree-ring cores can ascertain the age range of fire events, pinpointing the exact year remains challenging. In this study, we propose a novel approach for detecting fire occurrence years by recognizing abrupt shifts in the tree-ring geometric center (TRGC). This method entails extracting a minimum of three tree-ring cores from the uninjured side of the tree and in proximity to the fire scar. We validated this method’s efficacy using samples from Transbaikal of Russia, in northeastern Asia, where fire years have already been documented. Our results show that this method accurately identified the fire year in nine fire scars with a 67 percent probability of exact agreement with the actual fire year. It is noteworthy that this method particularly excels in cases of trees with a single fire scar. We recommend employing the traditional method of collecting tree-ring cores near the fire scar to establish the age range of the fire scar. Subsequently, within this determined range, we suggest detecting the shifts in the TRGC to accurately pinpoint the exact year of the fire scar.

Evapotranspiration demand has increased rapidly as temperatures have risen, affecting forest productivity. Consequently, carbon (C) uptake by forests is being modified; therefore, a more refined knowledge of the relationships between C capture and hydroclimate variability is required, particularly in drought-prone regions. In this study, we analyzed the relationships between climate and C capture as stemwood through the dendroecological analyses of radial growth in 15 conifer species distributed along a broad bioclimatic gradient in Mexico. The C content was calculated using densitometry data; correlations and mixed models were then used to determine the influence of climatic variables (precipitation, mean maximum and minimum temperatures, SPEI drought index) on tree growth. Each species showed specific responses to the climate with Taxodium mucronatum being the most responsive species. Both precipitation and maximum temperature best explained changes in C capture, with minimum temperature and SPEI playing secondary roles. The winter before the growth period was the most important season for C capture, particularly through positive responses to wet-cool conditions. However, the climatic influences of the current fall and summer were also notable. Seasonal climatic influences have implications for C uptake and forest productivity in the face of the severe droughts that repeatedly affect the study region.

To understand the impact of climate change on the tree radial growth in Southeast China’s subtropical evergreen broadleaved forest, comparative research on the radial growth–climate associations of Schima superba was conducted. This dominant evergreen broadleaved tree species was examined at both its southern and northern distribution margins through dendroclimatology. The results showed that the radial growth of S. superba stands at a high elevation in the southern margin and stands in the northern margin were positively correlated with springtime temperatures, mostly in April (e.g., mean temperature: r = 0.630, p < 0.05) and May (e.g., maximum temperature: r = 0.335, p < 0.05), respectively. Meanwhile, the temperature in the late rainy season had a significant negative effect on the radial growth of S. superba stands in the southern margin, including high-elevation stands (e.g., the mean temperature in previous and current September: r = −0.437 and −0.383, p < 0.05) and low-elevation stands (e.g., the mean temperature in previous August and October: r = −0.577 and −0.348, p < 0.05). It was shown that temperature was the key climatic factor affecting the radial growth of S. superba, and the response of radial growth to temperature had obvious spatial differences. The findings indicate that the radial growth of S. superba stands in warm growth environments will be negatively impacted by future climate warming. On the contrary, the radial growth of S. superba stands growing in relatively cold growth environments may benefit from warmer spring. The results enhance the understanding of tree growth responses to climate change in the subtropical forests of China.

In order to explore the impact of climate change on the ecosystem at high altitudes, dendroclimatology was used to study the response of radial growth of Juniperus squamata Buch.-Ham. ex D.Don to the rapid warming in Nangqian County over the past 60 years, and a tree-ring width chronology for 115 years was established. (1) Meteorological data showed that the temperature in Nangqian County of the Tibetan Plateau has increased continuously during the past 60 years, and the minimum temperature has had the most significant change (0.63 °C/10a), especially between 2000–2019 (0.12 °C/a). Over the same time period precipitation has not changed significantly (0.94 mm/a, p > 0.10). The standard chronology was used to reconstruct the mean temperature series from July to September in Nangqian meteorological station during the past 115 years (1905–2019). The explained variance of the reconstructed equation was 42.8% (40.8%, after adjusting for degrees of freedom). The reconstructed temperature series can be roughly divided into two stages: from 1905 to 1999, the temperature fluctuated around the average value, 12.10 °C, and from 2000 to 2019, the temperature showed a significant upward trend. (2) The analysis of the climate-tree growth relationship indicated that the response of radial growth of Juniperus squamata to temperature was significantly stronger than the response to precipitation; especially in the last 20 years, when the radial growth of Juniperus squamata was positively correlated with temperature (p < 0.01). Compared to the maximum temperature and mean temperature, the correlation between radial growth of Juniperus squamata and minimum temperature was more significant. (3) Under the background of climate warming, the radial growth trend of Juniperus squamata in Nangqian county was consistent with temperature changes. Particularly in the past 20 years, the radial growth of Juniperus squamata showed a significantly increased trend and entered a rapid growth period.

To model the global distribution pattern of maximum tree age (age of the oldest tree at a given site), we included only living trees that were >= 100 years old in the ITRDB (most sites have trees exceeding 100 years old) (Liu et al., 2019a). Keywords: global distribution; large old trees; longevity; tallest trees; tree ring; anillo de árbol; árboles más altos; árboles viejos grandes; distribución mundial; longevidad; : ; ; ; ; EN global distribution large old trees longevity tallest trees tree ring anillo de árbol árboles más altos árboles viejos grandes distribución mundial longevidad : 1 10 10 08/01/22 20220801 NES 220801 INTRODUCTION Extremely old trees are natural features that have important roles, such as generating insights about historical climatic events (Di Filippo et al., 2012; Yang et al., 2014), maintaining biodiversity and ecosystem function (Lindenmayer & Laurance, 2017; Stephenson et al., 2014), and providing social and cultural benefits to people (Blicharska & Mikusi'nski, 2014). According to the ITRDB database, there were 197,855 cored old trees, 620 trees (0.31%) >=1000 years, 18 trees (0.009%) >=2000 years, and 1 tree >3000 years old. Therefore, unlike the frequently reported extremely old trees >=2000 years in many countries (e.g., Black et al., 2018; Liu et al., 2019a), we found that local estimates of tree ages for extremely old trees based on tree diameters or tree height are probably inaccurate. [Extracted from the article]

Key message: The growth of Shorea robusta is positively correlated with temperature, whereas the relation to moisture is weak. Tree-ring analyses provide a rich archive of information on environmental attributes affecting tree growth. Tree-ring studies conducted so far have mostly focused on temperate species, and research on tropical trees is limited. This study aims to develop a tree-ring chronology of Shorea robusta and understand the climatic sensitivity of its growth in the tropical region of Nepal. Tree-ring samples of S. robusta were analysed following the standard dendrochronological sample analysis procedure. A 134-year-long ring-width chronology of S. robusta was developed, extending from 1851 to 2018, which is the longest chronology reported for this species. The chronology statistics revealed its high dendroclimatic potential with moderate R-bar, high expressed population signal, and low autocorrelation. The mean annual radial growth was 2.87 mm per year, while the mean basal area increment (BAI) was 9.245 cm2 per year. The ring width, BAI chronology and size-based growth analysis revealed an increasing growth trend of the species, which is likely favoured by the ongoing climate change. The tree growth of the species was positively correlated to temperature throughout the year; however, the relation to moisture parameters was weak. The temperature sensitivity of the species is stable over time, though a slight temporal difference exists in the strength of association. [ABSTRACT FROM AUTHOR]

Drought is a major natural disaster that has long-lasting effects on economic and social activities in northern China and has regional distinctions in duration, severity, and spatial extent. In this study, tree-ring chronologies and historical archives in the Yellow River Basin and its surrounding areas are collected to investigate the extreme drought history and dynamic process of the two extreme drought events for the past ~ 200 years. Instead of reconstructing climate indicators, the tree index is directly employed here to partly overcome the high-frequency information loss during tree-ring-based reconstruction. The results show that identified drought history is improved significantly relative to the single indicator reconstruction, and drought events are highly consistent with historical recorded ones. Two prominent drought events in modern Chinese history are analyzed, namely the Ding-Wu Great Famine (1876–1879) and the extreme drought in northern China during the late-1920s. Unexpectedly, the most prestigious Ding-Wu Great Famine is lower than the extreme drought in the late-1920s in terms of drought duration, spatial extent, and intensity. Our research further reveals that the drought events recorded in the historical records could be very different from actual events due to the influence of political and other factors. The analysis of spatial dynamics indicates that the potential mechanisms of the two drought events are also different. This is confirmed by research based on reanalysis data that the Ding-Wu Great Famine was caused by a typical strong ENSO event, while the mechanism of the extreme drought in the late-1920s was more complicated. [ABSTRACT FROM AUTHOR]

Micro-drilling resistance method is a widely used tree ring micro-destructive detection technology. To solve the problem that the detection signal of the analog micro-drilling resistance method has excessive noise interference and cannot intuitively identify tree ring information, this research proposes a digital micro-drilling resistance method and provides a recommended hardware implementation. The digital micro-drilling resistance method adopts the photoelectric encoder instead of ADC as the signal sampling module. Through the theoretical analysis of the DC motor characteristic, the PWM closed-loop speed control, the detection principle of the digital method is given. Additionally, the experimental equipment that can complete the detection of the digital method and the analog method simultaneously is designed to carry out comparative experiments. The experimental results show that: (1) The detection results of the digital method have a better-quality signal which can intuitively identify the tree rings. (2) The average correlation coefficient reaches 0.9365 between the detection results of the digital method and the analog method. (3) The average Signal-to-Noise Ratio (SNR) of the digital method is 39.0145 dB, which is 19.2590 dB higher than that of the analog method. The average noise interference energy in the detection result of the digital method is only 1.27% of the analog method. In summary, hardware implementation of the digital micro-drilling resistance method can correctly reflect the tree ring information and significantly improve the signal quality of the micro-drilling resistance technology. This research is helping to improve the identification accuracy of micro-drilling resistance technology, and to develop the application of tree ring micro-destructive detection technology in the high-precision field. [ABSTRACT FROM AUTHOR]

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree‐ring fire scars provide valuable perspectives on fire regimes, including centuries‐long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree‐ring fire‐scar network (NAFSN), which contains 2562 sites, >37,000 fire‐scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000‐m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire‐scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under‐sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non‐Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually‐ to sub‐annually‐resolved tree‐ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America. [ABSTRACT FROM AUTHOR]

Atmospheric heavy metal deposition is widely occurring due to anthropogenic effects such as industrial activities and motor vehicles. As a result, it has increased significantly and reached a level that threatens human health and the environment. Among these deposition factors, it is of great importance to monitor the atmospheric concentrations of heavy metals that do not easily degrade in nature, tend to bioaccumulate, and can be toxic even at low concentration levels. Biomonitoring is one of the most impressive passive methods in determining the change of heavy metal concentrations in the atmosphere. This study investigates the effect of anthropogenic emission sources in urban areas using tree rings as a biomonitor. Cedrus atlantica was selected, because it is generally preferred in parks, roadside and landscape design. Samples were collected from parks near the road, densely populated, and close to the small-scale industry in Kastamonu, Türkiye. Atmospheric deposition of Lead (Pb) and Cadmium (Cd) in organs were analyzed based on years and directions. Their accumulation in the outer bark was determined to be quite high (Cd value is 2226.2 ppb and Pb value is 38201.1 ppb) compared to other organs. As a result, the traffic density and industrial emissions affect the Pb and Cd concentrations. This study will provide beneficial information for atmospheric heavy metal deposition in landscape plants. [ABSTRACT FROM AUTHOR]

Tree resistance to extreme droughts and post‐drought recovery are sensitive to the drought timing. However, how the bioclimatic sensitivity of tree growth may vary with the timing and order of extreme droughts and wetness is still poorly understood. Here, we quantified the bioclimatic sensitivity of tree growth in the period of 1951–2013 under different seasonal extreme drought/wetness regimes over the extra‐tropical Northern Hemisphere, using 1,032 tree ring chronologies from 121 gymnosperm and angiosperm species. We found a negative asymmetry in tree growth under regimes with seasonal extreme droughts. With extreme drought, tree growth in arid and temperate dry regions is more negatively impacted by pre‐growing‐season (PGS) extreme droughts. Clade‐wise, angiosperms are more sensitive to PGS water availability, and gymnosperms to legacy effects of the preceding tree growth conditions in temperate dry and humid regions. Our finding of divergent bioclimatic legacy effects underscores contrasting trends in forest responses to drought across different ecoregions and functional groups in a more extreme climate. Plain Language Summary: The occurrence patterns of seasonal extreme drought and wetness events are dramatically shifting with climate warming. However, how will different seasonal extreme climate regimes affect the bioclimatic sensitivity of tree growth remains poorly understood. In this study, we investigated the sensitivity of tree growth to different seasonal climate factors and preceding tree growth conditions during 1951–2013 under different seasonal extreme drought/wetness regimes, using 1,032 tree ring chronologies covering 121 gymnosperm and angiosperm species. We found the magnitude in tree growth reduction caused by seasonal extreme drought events is much larger than that in tree growth stimulation by seasonal extreme wetness events in arid and temperate regions. Tree growth in arid and temperate dry regions is more negatively impacted by extreme drought events in pre‐growing‐seasons (PGSs) than in growing‐seasons. We further found that angiosperms are more sensitive to PGS water availability, while gymnosperms are more sensitive to legacy effects of the preceding tree growth conditions in temperate dry and humid regions. These findings highlight divergent bioclimatic legacy effects on tree growth under different seasonal extreme climate regimes, and provide valuable insights into the future trajectories of forest growth across diverse ecoregions and functional groups in a more extreme climate. Key Points: Negative asymmetry in tree growth was observed under regimes with seasonal extreme droughtsTree growth in arid and temperate dry regions is more vulnerable to extreme droughts in pre‐growing‐seasons than in growing‐seasonsAngiosperms are more sensitive to pre‐growing‐season water availability, and gymnosperms to legacy effects of the preceding tree growth [ABSTRACT FROM AUTHOR]

The ongoing 22‐year drought in the Upper Colorado River Basin (UCRB) has been extremely severe, even in the context of the longest available tree‐ring reconstruction of annual flow at Lees Ferry, Arizona, dating back to 762 CE. While many southwestern drought assessments have been limited to the past 1,200 years, longer paleorecords of moisture variability do exist for the UCRB. Here, gridded drought‐atlas data in the UCRB domain along with naturalized streamflow data from the instrumental period (1906–2021) are used in a K‐nearest neighbor nonparametric algorithm to develop a streamflow reconstruction for the Lees Ferry gage starting in 1 CE. The reconstruction reveals a second‐century drought unmatched in severity by the current drought or by well‐documented medieval period droughts in the UCRB. Although data are sparse, analysis of individual long tree‐ring records and other paleoclimatic data also support the occurrence of an exceptional second‐century drought. Plain Language Summary: The Colorado River drought we currently are experiencing is severe in the context of the 116‐year gage record (1906–2021), but how severe is it in a long‐term context? Existing tree‐ring based reconstructions of Colorado River streamflow have suggested that the 22‐year period 2000–2021 could be the worst drought in the southwestern United States in 1,200 years. The purpose of this study is to extend the Colorado River reconstruction back 2,000 years and to evaluate the current drought in a long‐term context. We find that an even more extreme drought occurred and persisted over much of the second century. Data are sparse this far back in time, but evidence from both tree‐ring data and paleoclimate data from lakes, bogs, and caves supports the existence and severity of this drought in the context of the last two millennia. Additional work is needed to learn more about this drought and its causes, but we now know that drought more persistent than even the well‐documented medieval period droughts occurred in the past, expanding our understanding of the range of natural climate variability. Key Points: A new tree‐ring based ensemble streamflow reconstruction spanning the last two millennia was developed for the Colorado RiverThe new reconstruction reveals a second‐century drought unmatched in severity by any past droughts in the Upper Colorado River BasinThe ongoing 22‐year period of low Colorado River streamflow is a rare event, but is not the most severe drought in the past 2,000 years [ABSTRACT FROM AUTHOR]

In recent decades, the global climate has changed significantly. The climate in Northwest China became warm-wet, especially in the Tianshan Mountains. In order to explore the response of tree growth to recent climate change, the two dominant trees species, Picea schrenkiana Fisch. et Mey. and Larix sibirica Ledeb., were studied with the dendrochronological method in the western Tianshan Mountains (WT) and the eastern Tianshan Mountains (ET). Our results showed that: (1) The tree growth of four sample sites in the WT significantly increased in recent decades, while the trees in the three sample sites in the ET significantly decreased. (2) In the WT, except for the Manas site, the tree-ring chronologies of the other three sites were significantly positively correlated with the mean annual minimum temperature. Tree-ring chronologies in the WT, except for Bangfanggou site, were significantly positively correlated with annual precipitation. In the ET, only the tree chronology of L. sibirica in the Balikun site was significantly negatively correlated with the annual temperatures, including the mean minimum, mean and mean maximum temperature. (3) The proportion of trees with a significant upward growth trend at each site decreased from west to east, and the proportion of trees with a significant downward growth trend at each site increased from west to east along the whole Tianshan Mountains. (4) The correlation of tree-ring chronologies with the annual temperature and annual precipitation was not stable during the study period. Warm-humidification promoted the growth of trees in the WT but inhibited tree growth in the ET, which may be exacerbated drought stress in the ET where the increase in precipitation was not enough to offset the increased evapotranspiration potential caused by warming. [ABSTRACT FROM AUTHOR]

Mining activity is often responsible for the drainage of acid or metal-enriched waters to fluvial systems. The release of metals is especially disturbing due to the toxicity and persistence of these products and their accumulation in the biosphere. Hence, a systematic detection and delimitation of highly polluted floodplains and linkages between pollution and high-flow stages would likely assist the improvement of land management and ease the design of mitigation or rehabilitation measures. Here we test how trees growing in different geomorphic positions along a fluvial system uptake metal during floods and how these uptakes can be documented “a posteriori”. To this end, we apply dendrogeochemical analyses to twenty Pinus pinaster Ait. trees growing on the banks of Odiel River (south-western Spain) as well as to five reference trees growing outside the river channel. In the field, trees were sampled with a large-diameter (1 cm) increment borer. In the lab, tree-ring series were dendrochronologically cross dated and separated into 5-yr blocks, so that wood blocks contained the dates of major floods. Then, Inductively Coupled Plasma Mass Spectrometry (ICPM) was employed to evaluate toxic metal concentrations in trees. Results point to clear correlations between the accumulation of toxic metals and the geomorphic position of trees within the fluvial network. We show that morphological units along a river exert control on toxic metal concentrations in trees, with uptake being much higher in trees located on meander cut banks than in trees growing on point-bar structures. Besides, we detect chemical signatures in trees located farthest away from the main river channel after the largest floods, but not in the aftermath of smaller events. We conclude that tree position is the single-most important determinant for metallic pollution in an environment controlled by fluvial processes, but also find that more studies are still needed to determine linkages with individual floods and interactions of metal uptake in roots via the water table in the river corridor.

Cosmogenic nuclides such as 14C from tree rings and 10Be and 36Cl from ice cores are excellent proxies for the past extremely large solar energetic particle (SEP) events, which are dozens of times larger than the largest SEP event in the history of observation. So far, several rapid 14C increases have been discovered, which are considered to have originated from extreme SEP events (or set of successive SEP events) from verifications using multiple cosmogenic nuclide analyses in natural archives. Although these events are characterized by a rapid increase in cosmogenic nuclide concentrations, 14C data recorded worldwide do not always show similar variations, especially during the 993 CE event, where a rapid increase was recorded in either 992–993 CE or 993–994 CE in several records. We present new 14C data of the Japanese cedar sample for the 993 CE event. Although the latest data show no significant increase in 1 year, an overall increase pattern is consistent with the previously reported 14C data of the Japanese cedar, which supports that a significant 14C increase occurred from 993 to 994 CE in the Japanese sample. Given the dominant 14C production in high latitudes by SEPs, the difference in timing of increase may be a transport effect in the atmosphere. Moreover, the difference in the timing of the 14C increase can cause a 1-year age-determination error using the 993 CE radiocarbon spike. Compared with the 14C data between tree samples from high latitude and midlatitude, including Japan, high-latitude data can capture 14C changes originating from SEP events more quickly and clearly and may be more suitable for a SEP event exploration in the past.

Abstract Tree resistance to extreme droughts and post‐drought recovery are sensitive to the drought timing. However, how the bioclimatic sensitivity of tree growth may vary with the timing and order of extreme droughts and wetness is still poorly understood. Here, we quantified the bioclimatic sensitivity of tree growth in the period of 1951–2013 under different seasonal extreme drought/wetness regimes over the extra‐tropical Northern Hemisphere, using 1,032 tree ring chronologies from 121 gymnosperm and angiosperm species. We found a negative asymmetry in tree growth under regimes with seasonal extreme droughts. With extreme drought, tree growth in arid and temperate dry regions is more negatively impacted by pre‐growing‐season (PGS) extreme droughts. Clade‐wise, angiosperms are more sensitive to PGS water availability, and gymnosperms to legacy effects of the preceding tree growth conditions in temperate dry and humid regions. Our finding of divergent bioclimatic legacy effects underscores contrasting trends in forest responses to drought across different ecoregions and functional groups in a more extreme climate.

Trees may represent useful long-term monitors of historical trends of atmospheric pollution due to the trace elements stored along the tree rings caused by modifications in the environment during a tree’s life. Chestnut (Castanea sativa Mill.) tree trunk sections were used to document the yearly evolution of atmospheric Hg in the world-class mining district of Monte Amiata (MAMD; Central Italy) and were exploited until 1982. An additional source of Hg emissions in the area have been the active geothermal power plants. A marked decrease (from >200 µg/kg to

• Investigated climate, GPP and xylem biomass in boreal and temperate Canadian forests. • Found strong GPP-biomass growth link in both forest types. • Boreal: cold growing seasons led to GPP and biomass growth reduction. • Temperate: drought linked to GPP and biomass growth reduction. Understanding the complex relationships between climate, forest carbon (C) uptake and biomass growth has become a research priority, crucial for assessing the climate change impacts on forest C sequestration. Such associations are expected to vary across biomes, due to different climate constraints on tree physiology. However, our understanding of the seasonal dynamics of long-term C sequestration and how climate influences them in different forest biomes is still limited. We investigated a boreal Pinus banksiana forest (Old Jack Pine, OJP) and a temperate Pinus strobus plantation (Turkey Point, TP39) in Canada. We aimed to assess the link between C uptake and above-ground woody biomass growth, and the effects of climate inter-annual variability on them. We used daily records of climate and gross primary productivity (GPP, period 1999–2019 at OJP and 2003–2018 at TP39), and investigated xylem biomass proxies at cell (cell wall area) and tree-ring level (ring wall area) from 1970 to 2019 at OJP, and from 1970 to 2018 at TP39. In both forests, the direct link between C sink and C source was revealed by the common inter-annual variability of GPP and xylem biomass. GPP and xylem biomass were mostly influenced by spring and late summer temperature at OJP. However, at both sites, summer drought negatively influenced GPP, and biomass growth especially in recent decades. Analysis of dry and cold years evidenced short-term negative effects of low temperature on GPP and xylem biomass in OJP, and of drought in TP39. Long-term intra-annual analyses are crucial to assess the variable effects of climate on forest C cycle. Warm spring and autumn can benefit both GPP and biomass growth, but even in the boreal forest, summer drought has negative impacts. Increasing dry spells, especially in the temperate site, could reduce future forest capacity to uptake C and fix it in wood biomass. [ABSTRACT FROM AUTHOR]

Dendrochronology utilizes mean values of individual tree-ring indices to average out noise and strengthen common signals, typically associated with climate. Expressed Population Signal (EPS) is commonly used to assess the degree to which a chronology represents the common signal. However, there is a lack of studies on how EPS reflects low-frequency signals. In this study, we propose a frequency-dependent EPS (FEPS) approach to evaluating the low-frequency signal strength. Extensive tests were conducted using tree rings from Chinese Loess Plateau. We found that as timescales lengthen, EPS decreases due to declining inter-series correlations, thus demanding larger sample sizes. This finding remains robust across different detrending methods, filtering methods, filter orders, and treatments for end effects. Determining sample sizes by standard EPS (common use of EPS with unfiltered series) has a limited impact on multi-year frequencies, but considerably influences timescales exceeding a decade. Our study reveals a prevalent underestimation of sample size requirements for robust multi-year and interdecadal signals estimation, and the FEPS approach is expected to potentially enhance our understanding of long-term climate dynamics. [ABSTRACT FROM AUTHOR]

In the context of global warming, climate change in river headwater regions and its drivers have attracted increasing attention. In this study, tree-ring width (TRW) chronology was constructed using tree-ring samples of fir (Abies faxoniana) in Dadu River Basin in the central part of the western Sichuan Plateau, China. Correlation analysis with climatic factors implies that the radial growth of trees in the region is mainly limited by temperature and has the highest correlation with the mean minimum temperature in summer (June and July) (R = 0.602, p < 0.001). On this basis, the TRW chronology was adopted to reconstruct variations in the mean minimum temperatures in summer from 1733 to 2010 in the upper reaches of Dadu River. The reconstruction equation was stable and reliable and offered a variance explanation rate of 36.2% in the observed period (1962~2010). In the past 278 years, the region experienced nine warm periods and ten cold periods. The warmest and coldest years occurred in 2010 and 1798, respectively, with values of 13.6 °C and 11.0 °C. The reconstruction was highly spatiotemporally representative and verified by temperatures reconstructed using other tree-ring data in surrounding areas. A significant warming trend was found in the last few decades. Moreover, the multi-taper method (MTM) analysis indicated significant periodic changes in quasi-2-year and 21–35-year periods, for which the El Niño Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO) could be the key controlling factors.

We compared climate–growth relationships (1956–2013) of two natural pedunculate oak (Quercus robur L.) stands with different water-holding capacities growing at the species distribution limit of the Mediterranean Region in NW Iberia. For this, tree-ring chronologies of earlywood vessel size (separating the first row from the other vessels) and latewood width were obtained. Earlywood traits were coupled to conditions during dormancy, whereby an elevated winter temperature appears to induce a high consumption of carbohydrates, resulting in smaller vessels. This effect was reinforced by waterlogging at the wettest site, whose correlation to winter precipitation was strongly negative. Soil water regimes caused differences between vessel rows, since all earlywood vessels were controlled by winter conditions at the wettest site, but only the first row at the driest one; radial increment was related to water availability during the previous rather than the current season. This confirms our initial hypothesis that oak trees near their southern distribution boundary adopt a conservative strategy, prioritizing reserve storage under limiting conditions during the growing period. We believe that wood formation is highly dependent on the balance between the previous accumulation of carbohydrates and their consumption to maintain both respiration during dormancy and early spring growth.

Along with tree ring width, carbon isotopes are also good proxies for climate change. Water use efficiency (WUE) can be calculated more quickly and accurately based on carbon isotopes. In this study, according to the principle of dendroclimatology, the sequence of δ13C and WUE of tree rings of Picea meyeri are built. Pearson correlation analysis and multiple regression analysis are used to explore the response of carbon stable isotopes of Picea meyeri to climate change, which revealed the relationship between δ13C of Picea meyeri and climatic factors. Based on δ13C, we calculated the WUE of Picea meyeri and analyzed its response to climate change. The main conclusions are as follows: (1) The δ13C of Picea meyeri decreases year-by-year from 1957 to 2020, in the range from −23.89‰~−21.67‰, and the average value is −22.67‰. The water use efficiency of Picea meyeri increases in the range from 17.26~61.31, with an average of 39.45. (2) The δ13C of Picea meyeri is negatively correlated with temperature, which has the highest correlation with the temperature of the growing season (c5–c9), and its coefficient is higher than that of the mean temperature of each month. (3) There is a significant positive correlation between WUE sequence and temperature. Meanwhile, due to the effect of precipitation and temperature, the Picea meyeri is subject to drought stress to some extent. Above all, temperature is the main climatic factor affecting the δ13C and WUE of Picea meyeri on Luya mountain.

The Rhododendron spp. (R. yedoense and R. mucronulatum) at high elevations of Mt. Halla in Jeju Island are the dominant species in the shrubland. Despite the recent damage to their growth due to climate change and the spread of Sasa spp., these species have not yet been studied systematically in Korea. Therefore, the current study aimed to verify the effect of abiotic factors, e.g., temperature and precipitation, and the spread of Sasa spp. as a neighbor species on their growth based on ring-width measurement data. In addition, the death years were dated using the cross-dating method developed in dendrochronology by comparing the individual ring-width time series from dead Rhododendron spp. with the corresponding chronology established using living trees. For the study, disk samples were obtained from 11 and 10 living R. yedoense and R. mucronulatum, respectively, to establish tree-ring time series. To investigate the death years, six disk samples were also collected from each shrub species. The relatively high occurrence of missing or discontinuous rings is a characteristic of shrubs, which makes tree-ring analysis difficult. Through cross-dating, it was verified that the R. mucronulatum and R. yedoense have 4.3% and 5.3% missing and/or discontinuous rings (the total number of missing and/or discontinuous rings/the total number of tree rings), respectively. All dead shrubs were successfully dated based on synchronization of the individual time series with the corresponding chronologies established using the cross-dated time series; nine shrubs died in the 2010s and the other two shrubs in 1996 and 2001, respectively. Most deaths occurred when Sasa quelpaertensis dominantly occupied the study sites. From the analysis of the relationships between the residual chronologies and the bioclimate predictors (BioClim), only R. mucronulatum showed reliable correlations with the Bio5 (maximum temperature of the warmest month) as +0.28 (p < 0.05) and the Bio18 (precipitation of warmest quarter) as −0.33 (p < 0.05). This result means that summer temperature is a limiting factor for the growth of R. mucronulatum. Through this study, it was verified that Rhododendron spp. at high elevations in Korea can be used for research using tree rings.

Bosten Lake Basin not only is a major source of drinking water for the residents of the surrounding area, but also maintains the ecological balance of the region. However, with the influence of climate change and human activities, the water level of Bosten Lake fluctuates sharply and has a great impact on the surrounding ecological environment. Therefore, the study of its historical water flow changes as a reference has become a focus of research. In this study, the radial growth of Schrenk spruces (Picea schrenkiana Fisch. et Mey.) significantly correlated with the tributary streamflow coming from the mountainous region near Bosten Lake Basin. On the basis of this good coherence, the tree-ring chronologies were used to reconstruct the streamflow for Huangshuigou River from the previous August to the present July (r = 0.766, p < 0.0001, n = 50). The reconstructed streamflow series matched observations well, explaining 63.3% of the variation in the observed streamflow of 1956–2005. Then, the sum of the streamflow reconstruction of Huangshuigou River and another two tree-ring-based streamflow reconstructions (Kaidu River and Qingshui River) was used to represent the hydrological variation of the upper catchment of Bosten Lake Basin, and the reconstruction sequence was 306 years. The 10.7, 5.5, and 2.1 year cycles of the power spectrum and wavelet analysis revealed that the runoff series reconstructed from tree-ring hydrometeorology was related to solar activity. Some dry and wet years in the reconstructed streamflow series of the upper catchment of Bosten Lake Basin corresponded to the historical record. During the wet years, the Indian Ocean was probably the main source of precipitation.

During biological invasions, the initial arrival and establishment of invading populations often go unnoticed for many years yet information on early invasion dynamics is key to understanding and managing invasions. We used the presence of ring discoloration, “rotholz”, in tree cores to date historical Adelges piceae outbreaks and reconstruct its invasion history in 14 Abies balsamea subsp. phanerolepis stands in West Virginia. In 2018, we collected and cross-dated tree ring samples from 676 cores. We measured ring width increments and recorded the presence of rotholz in each annually dated ring. Rotholz was present in tree cores sampled from each of the 14 study sites, with the first rotholz occurrence in 1952 and widespread evidence of rotholz as early as the 1980s. Time series of rotholz frequencies indicate two synchronized waves of elevated rotholz frequencies that were observed at most sites from 1998 to 2003 and again from 2006 to 2013, coincident with observed outbreaks. Unlike patterns of growth suppression found among trees affected by defoliating insects, we observed a significant and positive relationship between rotholz frequency and standardized growth increment. This relationship is consistent with earlier observations of abnormal growth among trees infested by A. piceae. Our samples of rotholz frequencies suggests that rotholz may be a better indicator of past outbreaks of A. piceae than growth. The presence of A. piceae and its role in hastening decline of these rare relic tree populations would lend support to increased attention for the search for A. piceae biological control agents to limit damage by this insect. [ABSTRACT FROM AUTHOR]

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Robust ecological forecasting of tree growth under future climate conditions is critical to anticipate future forest carbon storage and flux. Here, we apply three ingredients of ecological forecasting that are key to improving forecast skill: data fusion, confronting model predictions with new data, and partitioning forecast uncertainty. Specifically, we present the first fusion of tree‐ring and forest inventory data within a Bayesian state‐space model at a multi‐site, regional scale, focusing on Pinus ponderosa var. brachyptera in the southwestern US. Leveraging the complementarity of these two data sources, we parsed the ecological complexity of tree growth into the effects of climate, tree size, stand density, site quality, and their interactions, and quantified uncertainties associated with these effects. New measurements of trees, an ongoing process in forest inventories, were used to confront forecasts of tree diameter with observations, and evaluate alternative tree growth models. We forecasted tree diameter and increment in response to an ensemble of climate change projections, and separated forecast uncertainty into four different causes: initial conditions, parameters, climate drivers, and process error. We found a strong negative effect of fall–spring maximum temperature, and a positive effect of water‐year precipitation on tree growth. Furthermore, tree vulnerability to climate stress increases with greater competition, with tree size, and at poor sites. Under future climate scenarios, we forecast increment declines of 22%–117%, while the combined effect of climate and size‐related trends results in a 56%–91% decline. Partitioning of forecast uncertainty showed that diameter forecast uncertainty is primarily caused by parameter and initial conditions uncertainty, but increment forecast uncertainty is mostly caused by process error and climate driver uncertainty. This fusion of tree‐ring and forest inventory data lays the foundation for robust ecological forecasting of aboveground biomass and carbon accounting at tree, plot, and regional scales, including iterative improvement of model skill. [ABSTRACT FROM AUTHOR]

A dendroecological study of the annual ring parameters of Scots pine (Pinus sylvestris L.) trees growing in the forest-steppe and steppe zones of Eastern Transbaikalia has been carried out. Using the methods of digital anatomy of annual rings, two (Nov and Tz) tree-ring chronologies based on four parameters (annual ring width, earlywood width, latewood width, and latewood optical density) have been constructed for the studied territory for the first time. A comparative analysis of the chronologies has made it possible to evaluate tree growth parameters under conditions of the forest-steppe (Nov) and steppe (Tz) zones and reveal the presence of reliable relations between them. The calculation of moving correlation coefficients reveals period*s when correlation coefficients fell below reliable values, indicating the impossibility of constructing a generalized regional chronology for the forest-steppe and steppe zones of Eastern Transbaikalia. A comparison of the chronologies with the weather parameters (ground air temperature and precipitations), as well as with the calculated drought and moisture indices (Selyaninov's hydrothermal coefficient, Ped's drought index, and Palmer drought severity index (PDSI)) reveal the most sensitive characteristics of annual rings in the studied area. In the forest-steppe zone, the highest correlation coefficients are obtained between the average annual precipitation and the annual ring width (r = 0.59) or the earlywood width (r = 0.59), as well as between the average air temperature for a hydrological year and the latewood width (r = 0.51). For the trees from the steppe zone, the most significant correlation is revealed between the annual precipitation and the annual ring width (r = 0.43) or earlywood width (r = 0.43), as well as between the PDSI for June–September and the earlywood width (r = 0.52). [ABSTRACT FROM AUTHOR]

A tree-ring width chronology was developed from the Chinese pine (Pinus tabuliformis) in northern North China. To acquire a long-term perspective on the history of droughts in this region, the Standardized Precipitation Evapotranspiration Index (SPEI) from August of the previous year to February of the current year was reconstructed for the period of 1903–2012 AD. The reconstruction explained 46.6% of the instrumental records over the calibration period of 1952–2012. Five dry periods (1916–1927, 1962–1973, 1978–1991, 1994–1999 and 2002–2005) and three wet periods (1908–1915, 1928–1961 and 1974–1977) were found in the reconstructed period, and most of the dry years (periods) in the reconstruction were supported by historical records. Comparisons between the reconstruction and other nearby dryness/wetness indices and precipitation reconstructions demonstrated a good repeatability and high reliability in our reconstruction. Spatial correlation implied that the reconstruction could represent regional hydroclimatic characteristics on a larger regional scale. Significant periodicities and correlations were observed between the reconstructed data and the quasi-biennial oscillation (QBO), El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), which suggested that the hydroclimatic variation in northern North China may be closely connected to remote oceans. The significant and high correlation between the reconstructed series and sea surface temperatures (SSTs) in the eastern equatorial and Southeast Pacific Ocean indicated that ENSO may be the main factor influencing the regional climate. [ABSTRACT FROM AUTHOR]

The green belt of Kyiv includes several rare forest biotopes ringing the city and experiencing numerous disturbances and stressors derived from both urbanization processes and climate changes. The arboreal species perform multiple ecological function and influence overall forested ecosystems vulnerability to natural or anthropogenic factors. We have developed the radial growth chronology of Tilia cordata, a common native species in Ukraine, to investigate its climate sensitivity in an urban forest in Kyiv. We assessed relationships between the radial growth of seven trees and hydrothermal variables derived from daily data sets aggregated in intervals from 14 to 180 days instead of the conventional monthly resolution. The studied trees demonstrated a weak intercorrelation, but high subsample signal strength allowed us to perform further analysis. The overall analyses spanned common for all studied trees chronologies period 1977–2015 shows that precipitation governed the growth of Tilia cordata in Kyiv's forest, and the influence was significant in the interval between December of the resting period and May in the growing season. Temperatures averaged for March–May of the prior growth period had a weaker but significant negative impact on Tilia cordata growth. The co-inertia analysis shows that despite low intercorrelation between trees chronologies, individual growth patterns highly correlated with growth-to-climate relationships patterns suggesting that precipitations synchronized trees growth even in various microsites conditions of the studied forest. The age of the oldest studied trees, which had a mean growth rate of 0.95 mm per year, reached 300 years.

Tree-ring stable oxygen isotope (δ18OTR) demonstrates the enormous potential for revealing hydrological climate changes and large-scale atmospheric circulations. Here, we established the 210-year δ18OTR chronology of Pinus tabulaeformis Carr. in Baotou, southwest Inner Mongolia, North China. The regional precipitation δ18O (δ18OP) and June-July-August relative humidity (RHJJA) were the two dominant environmental factors controlling the δ18OTR changes. Since the 1930s, the increasing δ18OTR values ​in the study region reflected the drying trend due to reducing precipitation and increasing temperature. The δ18OTR series in Baotou generally exhibited stronger correlations with three Indian summer monsoon (ISM) indexes than three East Asian summer monsoon (EASM) indexes during 1948–2009 AD. However, the δ18OTR record also significantly correlated with one EASM index. These results indicated that the Asian summer monsoon played an essential role in modifying the δ18OTR values, and the ISM possibly had more considerable influence compared with the EASM. We also found that the δ18OTR record had a higher correlation with the central-Pacific El Niño-Southern Oscillation (ENSO) than that with eastern-Pacific ENSO, probably because of the more substantial impact of the central-Pacific ENSO on the ISM.

Climate warming and subsequent drought are predicted to alter local forest production and carbon budgets, the sensitivity of which may be site- and species-specific. Although a warmer and drier climate often constrains tree growth, whether trees grown in cool, wet regions across the Siberian forest can in turn be promoted remains unknown. Here, we aimed to investigate the historical growth tendency of Siberian forests in the Sayan Mountain areas and to explore how climate interacts to regulate their growth. We used ring-width data from Siberian pine (Pinus sibirica Du Tour) sampled from three sites in this area to establish a regional chronology and calculate percentage growth change (%GC) over the past 250 years. Bootstrapped correlation analysis between the regional ring-width chronology and climatic factors indicates the mean air temperature, though not precipitation, is more often positively linked to the radial growth of Siberian pines. The %GC series shows that, from 1966 to 2006, the rising temperatures in May resulted in a significant increase in the radial-growth rate of Siberian pines (r = 0.47, p < 0.05). Our study suggests that the positive growth rate anomaly is more likely to occur as temperatures rise in Southern Siberia.

Estimating long-term trends and short-term amplitudes requires reliable temperature (Temp) observations in the pre-industrial period when few in situ observations existed in the Arctic. Tree-ring materials are most available and used to reconstruct past Arctic Temp variations. However, most previous studies incorporated materials that are insensitive to local Temp variabilities. The derived reconstruction qualities are low (indicated by low calibration R2), and the uncertainties inherent in the various detrending methodologies are unknown. To reconstruct Arctic (N60°–N90°) summer (June–August) Temp in 1850–1900 and variations over the past centuries, we screened 1116 tree-ring width and tree-ring density records and applied four detrending functions (sf-RCS, RCS, MOD, and spline). In total, 338–396 records show significant correlations (p < 0.05) with the Climate Research Unit (CRU) Temp of the corresponding grid point. These records were selected and combined into a proxy record. The achieved Arctic summer Temp reconstruction explained 45–57% of the instrumental summer Temp variance since 1950. The 2012–2021 summer Arctic warming amplitudes (1.42–1.74 °C) estimated by Temp anomaly datasets extending back to 1850 are within the range derived from our reconstructions, despite using various detrending methods. These findings could suggest the Berkeley and HadCRU5 datasets interpolating Temp from a few (6–73) meteorological stations could still represent the mean Arctic Temp variation in 1850–1900, and the updated reconstruction can be used as a reliable reference for 1550–2007 Arctic summer Temp history.

Cosmogenic nuclides – 14C from tree rings and 10Be and 36Cl from ice cores serve as an effective proxy for past extreme solar energetic particle (SEP) events. After identifying the first signature of an extreme SEP event in 774 CE, several candidates have been found in these proxy archives, such as 993 CE, 660 BCE, and 7176 BCE. Their magnitudes have been estimated to be tens of times larger than that of the largest SEP event ever observed since the 1950s. Although a detailed survey of such extreme SEP events is ongoing, the detection of intermediate-sized SEP events that bridge the gap between modern observations and extreme events detected in cosmogenic nuclides has not progressed sufficiently, primarily because of the uncertainties in cosmogenic nuclide data. In this study, we measured 14C concentrations in tree rings in the 19th century (1844–1876 CE) to search for any increases in 14C concentrations corresponding to intermediate-size extreme SEP events. We utilized Alaskan tree-ring samples cut into early and latewoods to suppress the potential seasonal variations in intra-annual 14C data. Notably, no significant 14C variations were observed between early and latewoods (0.0 ± 0.3‰), and the annual resolution 14C data series displayed an error of ~ 0.8‰. Over the entire study period, no significant increase in 14C concentrations characterized by other candidates of extreme SEP events such as the 774 CE event was detected in the annual 14C data. The present result imposes a constraint on the SEP fluence when the largest class of recorded solar storms occurred (especially those in 1859 CE and 1872 CE).

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Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)