Search

The Himalayas experienced long-term climate changes and recent extreme weather events that affected plant growth and the physiology of tree species at high-elevation sites. This study presents the first statistically robust δ18OTR chronologies for two native pine species, Pinus roxburghii, and Pinus wallichiana, in the lower Nepalese Himalaya. The isotope chronologies exhibited 0.88‰ differences in overall mean isotope values attributed to varying elevations (460–2000 m asl). Comparative analysis of climate response using data sets from different sources and resolutions revealed the superiority of the APHRODITE (Asian Precipitation – Highly-Resolved Observational Data Integration Towards Evaluation) data set calibrated for the South Asian Summer Monsoon (SASM)-dominated region. Both species exhibited negative correlations with monsoon precipitation and positive correlations with temperature. However, during the peak monsoon season (July-August), daily resolved climate data disentangled statistically insignificant relationships, and revealed that δ18OTR is influenced by atmospheric moisture. Both congeneric species showed a decoupling between the chronologies after 1995. However, no significant change in air moisture origin and monsoon regime between the study sites was observed, indicating a consistent dominant moisture source during different monsoon seasons. Besides, we also observed the decreased inter-series correlation of both δ18OTR chronologies after 1995, with P. wallichiana experiencing a steeper decrease than P. roxburghii. The weakening correlations between and within the chronologies coincided with a regional drought during 1993–1995 in both sites, highlighting the strong regulation of local climate on the impact of regional extreme climate events. Our findings emphasise the importance of employing climate data with optimal spatial and temporal resolution for improved δ18OTR-climate relationships at the intra-annual scale while considering the influence of site-specific local environmental conditions. Assessing climate data sets with station data is vital for accurately interpreting climate change's impact on forest response and long-term climate reconstructions. [ABSTRACT FROM AUTHOR]

We present a new teak (Tectona grandis L.f.) tree-ring stable oxygen isotope (δ18OTR) chronology from Mae Tuen (MT) site, Tak province, northwestern Thailand at inter-annual (167-year, A.D.1850–2016) and intra-annual (A.D.2006–2016) timescales. The inter-annual δ18OTR chronology showed a significant negative correlation (r = −0.678, p < 0.01) with the May–October amount of regional rainfall obtained from CRU TS4.03. We established a linear regression model that explained 46.0% of the actual rainfall variance and reconstructed monsoon season rainfall back to A.D.1850. The seasonal variations in moisture conditions were reflected in inter-annual δ18OTR variability. The rainfall amount and δ18O in precipitation (δ18Op) mainly controlled intra-annual variations in teak δ18OTR. These results show that the variation in Thai teak δ18OTR is dominated by rainfall, highlighting the strength of δ18OTR as a monsoon rainfall proxy. [ABSTRACT FROM AUTHOR]

Abrupt changes in temperature have especially strong impacts on fragile ecosystems located in semi-arid regions. In this study, we analyzed tree-ring widths (TRW) of Mediterranean cypress (Cupressus sempervirens var. horizontalis) in the Zagros Mountains, Iran. Furthermore, we separately measured earlywood width (EWW) and latewood width (LWW) of Persian oak (Quercus brantii Lindl.) to examine if intra-annual resolution of tree-ring parameters of Q. brantii tree rings can be used as high-resolution paleoclimate proxies. Climate-growth relationships revealed that mean monthly maximum temperatures (Tmax) are a dominant factor determining radial tree growth and negatively affect both oak and cypress in the Zagros Mountains. Accordingly, we reconstructed two different seasonal windows of past Tmax variability, namely, January–March and June–August over the periods 1860–2015 and 1560–2015, respectively. Regime shift detection identified twelve warm and nine cold significant regime shifts in our summer Tmax reconstructions. The longest hot summer period occurred in the twentieth century, and two warm regime shifts occurred in 1999 and 2008. The highest values of the warm summer regime shift index occurred in 2008, which coincided with fungal pathogen attacks and insect outbreak of the oak leaf roller moth (Tortrix viridana L.) in the Zagros oak woodlands. Interestingly, we found common warm and cold periods in historic climate variability between the summer and winter Tmax reconstructions. Warm and cold regime shifts occurred simultaneously from 1955 to 2015, and significant regional warm summer and winter regime shifts have occurred between 2008 and 2015. The winter and summer Tmax reconstructions show high spatial correlations with large areas in West Asia, North Africa, and the eastern Mediterranean region. Our results strengthen initial studies on past climate variability in Iran and contribute to an enhanced understanding of past temperature variability in West Asia. [ABSTRACT FROM AUTHOR]

Palaeoclimatic evidence is necessary to place the current warming and drying trends of the Mediterranean region in a long‐term perspective of pre‐industrial variability. Annually resolved and absolutely dated climate proxies that extend back into medieval times are, however, limited to a few sites only. Here we present a network of long ring width chronologies from Pinus nigra tree‐line sites in northern Corsica (France) that cohere exceptionally well over centuries and support the development of a single high‐elevation pine chronology extending back to 974 CE. We apply various detrending methods to these data to retain high‐to‐low frequency ring width variability and scale the resulting chronologies against instrumental precipitation and drought observations to produce hydroclimate reconstructions for the last millennium. Proxy calibration and transfer are challenged by a lack of high‐elevation meteorological data, however, limiting our understanding of precipitation changes in sub‐alpine tree‐line environments. Our new reconstructions extend beyond existing records and provide evidence for low‐frequency precipitation variability in the central‐western Mediterranean from 974–2016 CE. Comparison with a European scale drought reconstruction network shows that regional predictor chronologies are needed to accurately estimate long‐term hydroclimate variability on Corsica. [ABSTRACT FROM AUTHOR]

We analyzed the tree-rings δ18O of Abies spectabilis (fir) growing at the subalpine treeline ecotone in the Magguchatti valley. The valley is located in the Indian summer monsoon (ISM) dominated region of western Himalaya and also receives snow precipitation derived by westerly disturbances (WDs) during the winter months. The 60 year developed (1960–2019 CE) tree-ring δ18O chronology revealed a strong positive correlation with the temperature of late winter and spring months (February to April). Strong negative correlations are also apparent for snowcover, soilmoisture, and relative humidity for the same spring season. Our findings partly contrast the significant correlation results of tree-ring δ18O with summer precipitation and drought indices recorded from other summer monsoon-dominated regions in the Himalayas. The spatial correlation analyses with sea surface temperatures (SSTs) and climate parameters showed subdued signals of tropical Pacific at the site, but with a shift to more moisture influx from the Arabian Sea during the last two decades. Moreover, a significant negative correlation with North Atlantic Oscillation further justifies the strongly captured spring temperature and snowcover signals and the weak effect of summer precipitation in fir trees. A temperature rising trend during the latter half of the 20th century and the elevation effect are taken as important factors controlling the moisture source at the treeline ecotone zones. [ABSTRACT FROM AUTHOR]

Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794–2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a more consensual picture of past climate variability. Tree rings are a crucial archive for Common Era climate reconstructions, but the degree to which methodological decisions influence outcomes is not well known. Here, the authors show how different approaches taken by 15 different groups influence the ensemble temperature reconstruction from the same data. [ABSTRACT FROM AUTHOR]

Tree-ring δ18 O values are a sensitive proxy for regional physical climate, while their δ13 C values are a strong predictor of local ecohydrology. Utilizing available ice-core and tree-ring δ18 O records from the central Himalaya (CH), we found an increase in east–west climate heterogeneity since the 1960s. Further, δ13 C records from transitional western glaciated valleys provide a robust basis for reconstructing about 3 centuries of glacier mass balance (GMB) dynamics. We reconstructed annually resolved GMB since 1743 CE based on regionally dominant tree species of diverse plant functional types. Three major phases became apparent: positive GMB up to the mid-19th century, the middle phase (1870–1960) of slightly negative but stable GMB, and an exponential ice mass loss since the 1960s. Reasons for accelerated mass loss are largely attributed to anthropogenic climate change, including concurrent alterations in atmospheric circulations (weakening of the westerlies and the Arabian Sea branch of the Indian summer monsoon). Multi-decadal isotopic and climate coherency analyses specify an eastward declining influence of the westerlies in the monsoon-dominated CH region. Besides, our study provides a long-term context for recent GMB variability, which is essential for its reliable projection and attribution. [ABSTRACT FROM AUTHOR]

To develop a high‐resolution paleoclimate proxy record facilitating adaptation measures on drought impacts, we constructed a regional composite tree‐ring chronology of teak (Tectona grandis) by combining three local site chronologies from southern Myanmar. Our regional tree‐ring record is strongly correlated with the November–April self‐calibrated Palmer drought severity index and enabled us to reconstruct drought variability for the period 1802–2016. The reconstruction explained 46.5% of the actual self‐calibrated Palmer drought severity index variance. Over the past two centuries, we detected one extreme (1812) and six severe drought years (1810, 1811, 1816, 1852, 1887, and 1980). Dry periods coincided with six major famines that occurred in India. Spatial correlation analyses revealed that drought occurrence is linked to broader‐scale atmospheric circulations of the Pacific and Indian Oceans, especially during the positive phase of the El Niño–Southern Oscillation. Our reconstruction provides a useful historical perspective for assessing adaptation measures intent on mitigating future drought impacts in Myanmar. Plain Language Summary: We developed a 226‐year‐long ring‐width regional chronology of teak by combining three site chronologies from southern Myanmar. Teak growth is mainly controlled by moisture availability during the dry season, making teak a suitable species for assessing drought variation in southern Myanmar. We reconstructed a 215‐year drought history and find prolonged droughts occurred in 1808–1823, 1837–1843, 1863–1876, 1883–1891, 1895–1901, 1908–1912, 1922–1930, 1941–1945, 1952–1963, 1976–1994, and 2010–2015. We also found a strong association between drought variability in southern Myanmar and sea surface temperatures in the Pacific and Indian Oceans, as well as the El Niño–Southern Oscillation phenomenon. The results are useful to devise necessary policies and strategies for coping with the adverse impacts of drought and protecting the livelihoods of regional populations. Key Points: The radial growth of teak in southern Myanmar is mainly limited by moisture availability during the dry seasonDry episodes in the past 200 years in southern Myanmar coincided with six major famines in India and other regional drought reconstructionsDrought variations in southern Myanmar may be linked to large‐scale climate drivers, mainly tropical SST variations and El Niño events [ABSTRACT FROM AUTHOR]

Beech is one of the most important forest tree species in Europe, hence possible adverse factors affecting its physiology and productivity can have strong ecological and economic impacts. In this context, four beech forests along a latitudinal gradient from southern Apennines to middle European lowlands were selected for chronological determinations of carbon isotope composition (δ13C) in tree-ring cellulose. The main objectives of this study were to assess (i) the effect of climate on the carbon signature of tree-ring cellulose (δ13C); (ii) the physiological response to recent CO2 concentration increment and to climatic variation; and (iii) the relationship between intrinsic water-use efficiency (iWUE, here the average long-term ratio of net photosynthesis to stomatal conductance) and growth of trees in different sites since 1950. Our results demonstrated that site climatic conditions peculiarly affect δ13C. In northern sites, a climatic control of summer precipitation and temperature on stomatal conductance was demonstrated by their opposite correlations with δ13C, negative and positive, respectively. Furthermore, an ‘earliness effect’ was suggested by a significant relationship between spring temperature and δ13C in the coldest sites and by a positive one between winter temperature and δ13C in the warmest ones. In all the study sites, during the maturity phase, a positive correlation between the increment of CO2 and iWUE was observed, due to an active response of trees to CO2 increment. This increment of CO2 was the main driver of the long term increasing trend of iWUE, resulting by an active response of trees to CO2 fertilization. Moreover, precipitation mostly influences positively and negatively the inter-annual variations of iWUE of the southernmost and northernmost sites, respectively. Overall, we observed a mean increment of 40% of iWUE. Moreover, the sensitivity of iWUE to the increase of CO2 was different between the northernmost and southernmost sites. Increasing iWUE was correlated to growth in the two sites during the release phase and we hypothesize a positive effect of silvicultural treatments. [ABSTRACT FROM AUTHOR]

We developed the first tree-ring width chronology from Quercus brantii Lindel for the period 1796–2015 in the southern Zagros Mountains, Iran, using standard dendrochronological procedures. Climate-growth relationships revealed that DecemberöFebruary precipitation has strong positive effects (r = 0.66; P < 0.01) on the species’ growth while mean temperature during the growing season has strong negative effects. Spatial correlations with Palmer Drought Severity Index (PDSI) and gridded precipitation data revealed that the chronology contains regional climate signals and tree growth variations may represent precipitation fluctuations over large areas of the Middle East. The linear regression model accounts for 44% of the actual DecemberöFebruary precipitation variance. The reconstructed precipitation revealed that over the period 1850–2015 extreme dry years occurred in 1870-71, 1898, 1960 and 1963-64, and extreme wet years occurred in 1851, 1885, 1916 and 1921 in the southern Zagros region. The longest dry period lasted 16 years and occurred from 1958 to 1973. Two-year consecutive wet and dry events showed the highest frequencies and the average length of dry and wet events were 2.9 and 3.6 years over the reconstructed period. Correlations between the long-term reconstructed precipitation and the North Atlantic Oscillation (NAO), Southern Oscillation Index (SOI), and Pacific Decadal Oscillation (PDO) confirmed the effects of teleconnection patterns on precipitation in the southern Zagros region. [ABSTRACT FROM AUTHOR]

Atmospheric circulations influence local and regional weather conditions and, thus, tree growth. To identify summer weather types relevant for tree growth, and their associated synoptic-scale circulation patterns, an atmospheric circulation tree ring index (ACTI) dataset, derived from 414 tree-ring sites across Asia spanning the period 1871-2010, was created. Modes of common variability in the ACTI dataset were compared with leading modes of observed summertime 500-hPa geopotential height. The first four ACTI modes (explaining 88%of the total variance) were associated with pressure centers over Eurasia, the tropics, and the PacificOcean. The high spatiotemporal resemblance between the leading circulationmodes, derived from both tree rings and 500-hPa geopotential height fields, indicates a strong potential for reconstructing large-scale circulation patterns from tree rings in Asia. This would allow investigations of natural atmospheric circulation variability prior to anthropogenic climate change and provide a means to validate model simulations of climate predictions. [ABSTRACT FROM AUTHOR]

The response of the growing season to the ongoing global warming has gained considerable attention. In particular, how and to which extent the growing season will change during this century is essential information for the Tibetan Plateau, where the observed warming trend has exceeded the global mean. In this study, the 1960-2014 mean length of the tree-ring growing season (LOS) on the Tibetan Plateau was derived from results of the Vaganov-Shashkin oscilloscope tree growth model, based on 20 composite study sites and more than 3000 trees. Bootstrap and partial correlations were used to evaluate the most significant climate factors determining the LOS in the study region. Based on this relationship, we predicted the future variability of the LOS under three emission scenarios (Representative Concentration Pathways (RCP) 2.6, 6.0, and 8.5, representing different concentrations of greenhouse gasses) derived from 17 Earth system models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). The averaged LOS on the Tibetan Plateau is 103 days during the period 1960-2014, and April-September minimum temperature is the strongest factor controlling the LOS. We detected a general increase in the LOS over the twenty-first century under all the three selected scenarios. By the middle of this century, LOS will extend by about 3 to 4 weeks under the RCPs 2.6 and 6.0, and by more than 1 month (37 days) under the RCP 8.5, relative to the baseline period 1960-2014. From the middle to the end of the twenty-first century, LOS will further extend by about 3 to 4 weeks under the RCPs 6.0 and 8.5, respectively. Under the RCP 2.6 scenario, however, the extension reaches a plateau at around 2050 and about 2 weeks LOS extension. In total, we found an average rate of 2.1, 3.6, and 5.0 days decade−1 for the LOS extension from 2015 to 2100 under the RCPs 2.6, 6.0, and 8.5, respectively. However, such estimated LOS extensions may be offset by other ecological factors that were not included into the growth model. The estimated lengthening of the growing season could substantially affect carbon sequestration and forest productivity on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Forests provide fundamental ecosystem services. Environmental changes are predicted to affect forest growth directly through increased environmental stressors, and indirectly by amplifying disturbance. To increase our understanding of effects of environmental changes and disturbance on Afromontane forest growth, we used tree-ring data collected from Juniperus procera trees from church forests in the northwest highlands of Ethiopia. We used structural change models to detect structural shift in growth trends. We applied Linear Mixed Effect Models (LMM) to compare growth rate differences between successive tree generations. The running mean method and radial growth pattern analysis were used to detect disturbance events. Three groups of generations were identified based on Basal Area Increment (BAI) rates. There are significant differences (χ 2  = 204.64, P < .001) among generations in pace of BAI, indicating that old generation trees grew at a slower pace than younger ones. Radial growth patterns were homogeneous for the old generation, but diverse in young trees. The observed high growth rates in the younger generation may have a negative effect on the longevity of the individuals and positively affect carbon accumulation in the biomass. Disturbance was detected in all generations, but worsened in the 20th century. About 35% of disturbances matched with climate extreme events, providing evidence that the disturbance is both human-induced (i.e., site-specific) and climate-induced. Thus, forest management plans should emerge from a sound understanding of climate-forest-human interaction. [ABSTRACT FROM AUTHOR]

Climate-related environmental and humanitarian crisis are important challenges in the Great Horn of Africa ( GHA). In the absence of long-term past climate records in the region, tree-rings are valuable climate proxies, reflecting past climate variations and complementing climate records prior to the instrumental era. We established annually resolved multi-century tree-ring chronology from Juniperus procera trees in northern Ethiopia, the longest series yet for the GHA. The chronology correlates significantly with wet-season ( r = .64, p < .01) and annual ( r = .68, p < .01) regional rainfall. Reconstructed rainfall since A.D. 1811 revealed significant interannual variations between 2.2 and 3.8 year periodicity, with significant decadal and multidecadal variations during 1855-1900 and 1960-1990. The duration of negative and positive rainfall anomalies varied between 1-7 years and 1-8 years. Approximately 78.4% (95%) of reconstructed dry (extreme dry) and 85.4% (95%) of wet (extreme wet) events lasted for 1 year only and corresponded to historical records of famine and flooding, suggesting that future climate change studies should be both trend and extreme event focused. The average return periods for dry (extreme dry) and wet (extreme wet) events were 4.1 (8.8) years and 4.1 (9.5) years. Extreme-dry conditions during the 19th century were concurrent with drought episodes in equatorial eastern Africa that occurred at the end of the Little Ice Age. El Niño and La Niña events matched with 38.5% and 50% of extreme-dry and extreme-wet events. Equivalent matches for positive and negative Indian Ocean Dipole events were weaker, reaching 23.1 and 25%, respectively. Spatial correlations revealed that reconstructed rainfall represents wet-season rainfall variations over northern Ethiopia and large parts of the Sahel belt. The data presented are useful for backcasting climate and hydrological models and for developing regional strategic plans to manage scarce and contested water resources. Historical perspectives on long-term regional rainfall variability improve the interpretation of recent climate trends. [ABSTRACT FROM AUTHOR]

To better understand long-term drought variations in the central Himalaya, we developed new tree-ring width chronologies of Himalayan spruce ( Picea smithiana (Wall.) Boiss.) from three sites in the north-western Nepal. The local site chronologies showed high cross correlations and similar growth-climate responses to regional spring drought variability. We thus combined all site chronologies into a regional composite (RC) standard chronology that spans 516 years (1498–2013 CE). The RC chronology showed significant positive (negative) correlations with spring (March–May) precipitation (temperature) variability. Meanwhile, RC chronology showed the highest correlation with spring self-calibrating Palmer drought severity index (scPDSI, r = 0.652, p < 0.001), indicating that radial growth of P. smithiana is strongly limited by spring moisture availability. Using RC chronology, we reconstructed the spring drought variability for the period 1725–2013, which explained 42.5% variance of the actual scPDSI during the calibration period 1957–2012. Our reconstructed spring drought variability in the central Himalaya showed consistent wet-dry episodes with other regional drought and precipitation reconstructions from the Himalaya and nearby regions. Spectral peaks and spatial correlation analysis indicate that spring drought variability in the central Himalaya may be linked to large scale climatic drivers, mainly Atlantic Multidecadal Oscillation activities due to sea surface temperatures variation in the Atlantic Ocean. Our reconstruction revealed a continuous shift toward drier conditions in the central Himalaya since early 1980s that coincide with continental-scale warming and reduced spring precipitation in the central Himalaya. [ABSTRACT FROM AUTHOR]

Phenological responses of vegetation to climate, in particular to the ongoing warming trend, have received much attention. However, divergent results from the analyses of remote sensing data have been obtained for the Tibetan Plateau (TP), the world's largest highelevation region. This study provides a perspective on vegetation phenology shifts during 1960-2014, gained using an innovative approach based on a well-validated, process-based, tree-ring growth model that is independent of temporal changes in technical properties and image quality of remote sensing products. Twenty composite site chronologies were analyzed, comprising about 3,000 trees from forested areas across the TP. We found that the start of the growing season (SOS) has advanced, on average, by 0.28 d/y over the period 1960-2014. The end of the growing season (EOS) has been delayed, by an estimated 0.33 d/y during 1982-2014. No significant changes in SOS or EOS were observed during 1960-1981. April-June and August-September minimum temperatures are the main climatic drivers for SOS and EOS, respectively. An increase of 1 °C in April-June minimum temperature shifted the dates of xylem phenology by 6 to 7 d, lengthening the period of tree-ring formation. This study extends the chronology of TP phenology farther back in time and reconciles the disparate views on SOS derived from remote sensing data. Scaling up this analysis may improve understanding of climate change effects and related phenological and plant productivity on a global scale. [ABSTRACT FROM AUTHOR]

A profound consideration of stable oxygen isotope source water origins is a precondition for an unambiguous palaeoenvironmental interpretation of terrestrial δ O archives. To stress the influence of air mass origins on widely used δ O tree-ring chronologies, we conducted correlation analyses between six annually resolved δ O tree-ring cellulose ( $\delta ^{18}\textit {O}_{TC}$ ) chronologies and mean annual air package origins obtained from backward trajectory modeling. This novel approach has been tested for a transect at the southeastern Tibetan plateau (TP), where air masses with different isotopic composition overlap. Detailed examinations of daily precipitation amounts and monthly precipitation δ O values ( $\delta ^{18}\textit {O}_{P}$ ) were conducted with the ERA Interim and Laboratoire de Météorologie Dynamique General Circulation Model (LMDZiso) data, respectively. Particularly the southernmost study sites are influenced by a distinct amount effect. Here, air package origin $\delta ^{18}\textit {O}_{TC}$ relations are generally weaker in contrast to our northern located study sites. We found that tree-ring isotope signatures at dry sites with less rain days per year tend to be influenced stronger by air mass origin than tree-ring isotope values at semi-humid sites. That implies that the local hydroclimate history inferred from $\delta ^{18}\textit {O}_{TC}$ archives is better recorded at semi-humid sites. [ABSTRACT FROM AUTHOR]

Dendrochronological methods have been used to reconstruct insect outbreaks, yet the application has been scarce in the high Asia. We compiled tree-ring data from 4 host (Larix potaninii) and 4 non-host (Abies and Picea) sites in the central Hengduan Mountains, southwestern China. We assessed site-specific growth-climate responses and applied two methods to detecting larch insect defoliation events during the past 250 years. Compared with the non-host chronologies, larch trees (host) showed periodic reduction in radial growth, which may be associated with outbreaks of a larch defoliator. Synchronously, growth reductions was found for three low-elevation sites, such as during 1783–1790, 1846–1850, 1860–1865, 1873–1878, 1900–1909, 1939–1945, 1965–1970 and 1981–1986. However, these periods of outbreaks differ from those of a high-elevation site. With spectral analyses, we found 11–13 years frequency domains for three low-elevation larch chronologies, while 7–9 year peaks presented one high-elevation site. Contrastively, no significant frequency domains within the same periodicity were found in ring-width chronologies of co-occurring non-host species. We provide tree-ring evidence that larch trees growing in the central Hengduan Mountains have been infected by insect defoliators repeatedly. We suggest that appropriate approaches should be applied to correct insect-defoliation signals when using larch tree-ring data as a climatic proxy. [ABSTRACT FROM AUTHOR]

In recent decades, the Tibetan plateau (TP) experienced a distinctive temperature increase, with fundamental consequences for the hydrological system. As meteorological time-series extending back more than 60 years are scarce, there is a strong need for proxy data providing insight into the regional hydroclimatic history as well as the long-term variability. Within this study, a recently developed annually resolved 1500 year-long tree-ring stable oxygen isotope (δ 18 O) time from the southeastern TP is presented. Climate–proxy relationships reveal a strong impact of relative humidity (rH) during the summer months (May to September) on tree-ring δ 18 O, explaining around 45% of its variance. The derived reconstruction of relative humidity reveals a recent trend towards drier conditions on the TP. However, the present low rH level is not unprecedented in regard to the last 1500 years. In comparison to recent climate conditions, the Medieval Warm Period (MWP) was characterized by more stable conditions with higher humidity values. Hydroclimatic conditions during the Little Ice Age (LIA) suggest a contrasting two-phased period, with a clear shift from drier conditions prevailing between 1400 and 1650 AD to more humid conditions since the second half of the 17th century. Comparisons with other local proxies from lake levels and Pollen data from the southern part of the Tibetan plateau indicate a common regional climate forcing during the MWP and the LIA which can be related to changes in summer monsoon activity. However, the strength of the distinct dryness trend during the 20th century seems unique. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, we examine the relationship between short- and long-term effects of precipitation deficits, integrated in a drought index called 'Joint Deficit Index ( JDI)', and tree-ring growth of oak trees ( Quercus infectoria) in the Javan-Roud region, Kermanshah province (Iran). Precipitation data from regional climate stations cover the period 1968-2008, and the tree-ring width chronology span over the period 1818-2008. This chronology is highly correlated with the JDI (January-September) series for the instrumental period ( P < 0.01). Therefore, the regional JDI was reconstructed using a simple linear regression model which accounts for 40% of JDI (January-September) variances over the instrumental period. Reconstructed drought periods persisted on average for 2 years, and some severe drought lasted for 3-4 years. However, one 7-year drought was reconstructed over the period 1923-1929. The most severe droughts occurred in the periods 1960-1963 and 1999-2001. While the reconstructed JDIs have no significant correlation with the North Atlantic Oscillation, a significant negative correlation was observed with the Southern Oscillation Index in November and December of pre growth during the common period from 1877 to 2008. An appropriate agreement was found between our reconstruction and historical famines in Iran and also reconstructed results from neighbouring countries in the east (China) and west (Turkey and other countries around the Mediterranean Sea), particularly for the most severe droughts. The highest agreement was achieved with regions in the pathway of westerly storm tracks travelling via the Mediterranean region into Iran. [ABSTRACT FROM AUTHOR]

We present a newly developed, annually resolved tree-ring cellulose δO chronology for the southeastern Tibetan Plateau (TP) from Sikkim larch ( Larix griffithii), spanning between 1684 and 2012. Comparisons with local and regional climate data reveal strong positive correlations with monthly sunshine hours, temperature and daily temperature amplitude as well as strong negative correlations with relative humidity, vapor pressure, rain days per month and cloud cover of August. Relationships with local and regional tree-ring δO chronologies are stable and highly significant. Over the 20th century, we find no long-term climatic trends. This is consistent with other tree-ring δO chronologies of other tree species south of the Himalayas, but contrasts with results from isotope studies north of the Himalayas. This suggests stable macroclimatic flow patterns throughout the last centuries for the southern tree stands. In terms of large-scale climate dynamics, we find evidence of a significant 30-year wave influencing our tree-ring oxygen chronology, most probably induced by the Indian Ocean Dipole and influencing tree-ring oxygen isotope chronologies along the southeastern Himalaya and the southeastern rim of the TP. This pattern is spatially and temporarily consistent among the chronologies and has apparently strengthened during the last century. During periods of strong positive dipole mode activity, the dipole mode index shows positive correlations with the δO of tree-rings on the southeastern TP. [ABSTRACT FROM AUTHOR]

Tree rings are natural archives of climate and environmental information with a yearly resolution. Indeed, wood anatomical, chemical, and other properties of tree rings are a synthesis of several intrinsic and external factors, and their interaction during tree growth. In particular, Intra-Annual Density Fluctuations (IADFs) can be considered as tree-ring anomalies that can be used to better understand tree growth and to reconstruct past climate conditions with intra-annual resolution. However, the ecophysiological processes behind IADF formation, as well as their functional impact, remain unclear. Are IADFs resulting from a prompt adjustment to fluctuations in environmental conditions to avoid stressful conditions and/or to take advantage from favorable conditions? In this paper we discuss: (1) the influence of climatic factors on the formation of IADFs; (2) the occurrence of IADFs in different species and environments; (3) the potential of new approaches to study IADFs and identify their triggering factors. Our final aim is to underscore the advantages offered by network analyses of data and the importance of high-resolution measurements to gain insight into IADFs formation processes and their relations with climatic conditions, including extreme weather events. [ABSTRACT FROM AUTHOR]

Wood anatomical features may be visible on the microscopic as well as on the macroscopic scale. While the former can often be quantified by detailed wood anatomical analyses, the latter are often treated as qualitative features or as binary variables (present/absent). Macroscopic tree-ring features can be quantified in terms of frequency, intensity, or classified according to their position within a tree ring, like intra-annual density variations (IADFs) in conifers or frost rings in earlywood or latewood. Although some of these tree-ring features, like e.g. missing rings or IADFs are often seen as anomalies, hampering dendrochronologists to perform proper crossdating of tree-ring series, many of these properties are formed under extreme environmental stress or heavy impact, and could mark these extreme events by the manifestation in the wood anatomical structures throughout the lifespan of trees. The described tree-ring features form discrete time-series of extreme events. For example, flood rings may be marked by lunar-shaped earlywood vessels or enlarged latewood vessels in ring-porous oaks. White earlywood rings and light rings indicate reduced cell wall thickness and lignification occurring in very cold years. Frost rings result from cambial cell death during abrupt cooling events in the growing season. Missing rings and IADFs are mainly caused by drought events. Characteristic variations in earlywood vessel size, shape, or number in ring-porous oak species are markers for flood events, defoliation, heat stress, or drought. Traumatic resin ducts may be triggered by a range of biotic or environmental stressors, including wounding, fires or mechanical factors. Reaction wood is indicative of mechanical stress, often related to geomorphic events. In many cases anatomical responses are unspecific and may be caused by different stressors or extreme events. Additionally, the sensitivity of trees to form such features may vary between species, or between life stages within one species. We critically evaluate the indicative value of different wood anatomical tree-ring features for environmental reconstructions. [ABSTRACT FROM AUTHOR]

Copyright of Erdkunde is the property of Universitaet Bonn, Geographisches Institut 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.)

As the northern fringe of the Asian summer monsoon region, north-central China (hereafter NCC) is highly sensitive to climate change. It is important to understand drought variability and the associated mechanisms in this region since precipitation changes have direct impacts on human society in this semiarid-arid area. In this study, a new tree ring-width based drought reconstruction (AD 1804-2010) was established in the Songmingyan Nature Reserve, which lies in NCC. This reconstruction illustrates the severe drought periods occurring in the 1860s, 1928-1932 and 1991-2000, with recurring drought intervals being about 60 years. The first principal component of the five chronologies from NCC shows strongly coherent drought variability with the other single-site records and can thus be used as an indicator of regional moisture variations. Combining the Monsoon Asia Drought Atlas (hereafter MADA) dataset and the dry-wet index (hereafter DWI) dataset from eastern China, the spatial distribution of moisture variability for three selected drought events is mapped. It is found that northern China and Mongolia experienced dry conditions during the three severe drought periods, whereas wet conditions prevailed in the middle and lower reaches of the Yangtze River. The Pacific Decadal Oscillation (hereafter PDO) might have been one of the possible causes responsible for multi-decadal drought variability over NCC, with the PDO warm phases being associated with drought conditions and the cold phases corresponding to wet conditions over NCC. [ABSTRACT FROM AUTHOR]

Knowledge of Asian monsoon variability remains limited because of sparse instrumental data available only for short time series. Here, an updated tree-ring width record covering the period ad 1037–2009 was developed for the south-central Tibetan Plateau (TP). Correlation analysis revealed a significant relationship (r = 0.71) between the tree-ring index and annual (previous July to current June) precipitation series for the instrumental period 1963–2008, which accounts for 50.41% of the rainfall variability. Based on a linear regression model, the longest available regional precipitation history was reconstructed. Spatial correlation between tree ring width and annual precipitation data from previous July to current June indicates that the reconstruction is representative of precipitation changes on the south-central TP. Regional wet conditions occurred during ad 1095–1161, 1376–1403, 1414–1446, 1518–1537, 1549–1572, 1702–1757, 1848–1878 and 1891–1913, while dry periods were identified during ad1189–1242, 1256–1314, 1329–1357, 1470–1491, 1573–1623, 1636–1686, 1761–1821, 1823–1847, 1879–1890 and 1931–1985. The negative correlation between our reconstructed precipitation and India monsoon rainfall series indicates the seesaw pattern over northern and southern monsoon Asia. It is suggested that solar radiation-induced sea surface temperature (SST) anomalies over the tropical Pacific influence regional rainfall patterns. The degree of this influence has been stable at the multidecadal scale during the past 1000 years. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution proxy data are still scarce in the southeastern Tibetan Plateau, which limit our understanding of climatic variability before instrumental records. In this study, we developed 595-year tree ring-width chronology from Larix speciosa near the timberlines of the Gaoligong Mountains, southeastern Tibetan Plateau. Ring-width site chronologies and a well-replicated regional chronology (RC) showed significant positive correlations with warm season temperatures from May to August. Using RC as predictor, we reconstructed mean May–August temperature for the study region that extends back to A.D. 1585. Cold conditions prevailed during the periods 1600s, 1620–30, 1640–50s, 1700s, 1730–40s, 1760s, 1810–20s, 1850s, 1900–10s and 1955–70. Warm episodes occurred during 1610s, 1660–1680s, 1710–20s, 1750s, 1780–90s, 1820–40, 1920–50 and 1980–present. Spatial correlations with gridded land surface temperatures revealed that our reconstruction represents regional temperature signal for the southern Tibetan Plateau. Comparison with other tree ring-based temperature reconstructions from surrounding areas implies a high degree of confidence for our reconstruction. [ABSTRACT FROM AUTHOR]

The article presents a study on the temperature history recorded by tree rings in the Tibetan Plateau (TP), China during 1612-1998. The study develops two ring-width index chronologies such as traditionally standardized chronology (TSC) and regional curve standardization (RCS) for detrending. The results show that low-frequency and high-frequency temperature variations are captured by RCS and TSC reconstructions, and the response patterns of RSC chronology to climate data are similar to the TSC.

tree ring-width record spanning from AD 1377-1998 was developed from Tibetan juniper (Cupressus gigantea) growing at sites north of the deep gorge of the Yarlung Tsangbo River of southeast Tibet. A linear regression model between ring width and mean January-June temperature accounts for 35% of January-June temperature variance for the period 1961-1998. Based on this model, we reconstructed January-June temperature variation history for the study region during the past 622 years. Warm conditions occurred during AD 1385-1418, 1443-1466, 1482-1501, 1523-1548, 1570s, 1705-1759, 1770-1790, 1851-1888, 1910s, and 1938-1965, and periods of relatively cold years are identified forAD 1419-1442, 1470s, 1502-1522, 1550-1569, 1610-1640, 1680-1700, 1760s, 1791-1850, 1900s and 1965-1995. Spatial correlation between tree rings and observed temperatures indicates that the reconstruction is representative of temperature change for southeast Tibet. Regional cold conditions during AD 1625, 1685, 1760, 1800-1850, 1890-1930 and 1965-1995, and warm conditions during 1710, 1730-1750, 1850-1890 and 1930-1960 can be identified in the eastern Tibetan Plateau. Our reconstruction shows good agreement with modelled regional temperatures derived from an ECHO-G model simulation. Common cold periods around 1470, 1685 and 1845 corresponding to the Spörer Minimum, the Maunder Minimum and the Dalton Minimum periods of low solar activity and increased volcanic activity were identified, indicating that solar and volcanic activity played an important role in temperature change of this region. The discrepancy between modelled and reconstructed temperatures was noted around 1965, reflecting that temperature decrease in the late 20th century (1965-1995) is anomalous. [ABSTRACT FROM AUTHOR]

Abstract: Improved understanding of tree-growth responses to climate is needed to model and predict forest ecosystem responses to current and future climatic variability. We applied dendroclimatological techniques to assess the effects of inter-annual climate variations on radial growth of high-elevation conifers in the central Hengduan Mountains, southwestern China. Eight tree-ring width chronologies of the major tree genera Abies and Picea that are aligned along an elevation gradient from 3200 to 4200m a.s.l. were developed. Correlation and principal component analyses for the eight chronologies identified three groups of sites, representing different patterns of growth–climate relationships. Correlation and redundancy analyses with regional climate data revealed that radial growth of fir growing at high-elevation sites is enhanced by normal or warm summer temperatures (June and July) during the current growing season. In addition, radial growth of trees growing from high to middle elevations is sensitive to low temperatures during winter season. At low-elevation sites, trees display low sensitivity to temperature variation. However spring moisture availability becomes crucial for radial growth regardless of tree species. High- to middle-elevation conifers in the central Hengduan Mountains may benefit from the current climate warming, especially from rising winter temperatures. [Copyright &y& Elsevier]

The article discusses a tree ring-based drought reconstruction in the central Hengduan Mountains in north-western Yunnan, China. The study involved developing four tree ring-width chronologies of three species. It was found that there are correlations existing among the chronologies, and that the first principal component makes up 60.5% of total variance in 1655-2005. Also, radial growth was observed to be affected by precipitation and relative humidity and Palmer drought severity index (PDSI), whereas tree growth is negatively affected by temperature in March.

Abstract: We developed five tree ring-width chronologies from one fir (Abies georgei) and four spruce (Picea brachytyla) stands near the upper treeline in the central Hengduan Mountain, northwestern Yunnan, China. Similar growth patterns and significant correlations are embodied among the five chronologies. A principal component analysis for the four spruce chronologies indicated that the first component accounts for 54.8% of the total variance over the period 1750–2003. Climate–growth response analysis revealed that radial growth is mainly controlled by temperature variations, especially in the winter season. The first principal component of the spruce chronology network accounts for 43% of the annual mean temperature (from previous October until September) variance during the common period 1959–2003. By using a linear regression approach, we reconstructed annual mean temperature for the past 250 years. The reconstruction shows that the central Hengduan Mountain experienced some cool episodes during the 1810s, 1860s, and during 1960–1980. Warm intervals occurred during the 1780s, 1850s, 1940–1960 and in the past two decades. These general patterns are in general accordance with other records from nearby regions. [Copyright &y& Elsevier]

Maximum latewood density (MXD) measurements from long-lived Black pines (Pinus nigra spp. laricio) growing at the upper treeline in Corsica are one of the few archives to reconstruct southern European summer temperatures at annual resolution back into medieval times. Here, we present a compilation of five MXD chronologies from Corsican pines that contain high-to-low frequency variability between 1168 and 2016 CE and correlate significantly (p < 0.01) with the instrumental April–July and September–October mean temperatures from 1901 to 1980 CE (r = 0.52−0.64). The growth–climate correlations, however, dropped to −0.13 to 0.02 afterward, and scaling the MXD data resulted in a divergence of >1.5 °C between the colder reconstructed and warmer measured temperatures in the early-21st century. Our findings suggest a warming-induced shift from initially temperature-controlled to drought-prone MXD formation, and therefore question the suitability of using Corsican pine MXD data for climate reconstruction. [ABSTRACT FROM AUTHOR]

The inter-annual variability in tree-ring cellulose δ13C (δ13CTR, δ18OTR), and tree-ring chronology in teak (TRW) (Tectona grandis L.f.) trees from Northwestern Thailand during 1901–2009 AD was performed. The δ13CTR and δ18OTR have a positive correlation, significant at r =0.400, p <0.0001, and both of the stable isotopes were not significantly related to the TRW. The TRW is related to rainfall in the first half of the rainy season and has a strong relationship with the relative humidity. The δ18OTR captured moisture well throughout the rainy season, and the δ13CTR had a strong correlation with rainfall in the second half of the rainy season and had a high correlation with cloud fraction and vapor pressure. The δ13CTR and δ18OTR were associated with the stomata conductance response, but had no effect on photosynthesis. The three indices of the teak annual ring respond well to the variability in the Asian monsoon, and give us a better understanding of both the hydrological cycle and the factors that contribute to the growing of tropical broadleaf trees under changing climates. [ABSTRACT FROM AUTHOR]

Identifying what determines the high elevation limits of tree growth is crucial for predicting how treelines may shift in response to climate change. Treeline formation is either explained by a low-temperature restriction of meristematic activity (sink limitation) or by the photosynthetic constraints (source limitation) on the trees at the treeline. Our study of tree-ring stable isotopes in two Tibetan elevational transects showed that treeline trees had higher iWUE than trees at lower elevations. The combination of tree-ring δ13C and δ18O data further showed that photosynthesis was higher for trees at the treeline than at lower elevations. These results suggest that carbon acquisition may not be the main determinant of the upper limit of trees; other processes, such as immature tissue growth, may be the main cause of treeline formation. The tree-ring isotope analysis (δ13C and δ18O) suggests that Tibetan treelines have the potential to benefit from ongoing climate warming, due to their ability to cope with co-occurring drought stress through enhanced water use efficiency. [ABSTRACT FROM AUTHOR]

We developed a stable oxygen isotope chronology of tree-ring alpha cellulose (δ18O TR) from archaeological teak (Tectona grandis L.f.) samples from Mae Hong Son (MHS) province, northwestern Thailand. The samples were collected from ancient coffins belonging to the log coffin culture excavated at the Ban Rai rock shelter (BR). The chronology spans a period of 283 years in the late Holocene (AD14–296). The oxygen isotopic composition of BR δ18O TR ranged from 21.15‰ to 26.31‰. Since δ18O TR variations in Thailand teak can be used as indicators for precipitation amount during the rainy summer monsoon season, our chronology can be used as a proxy for regional late Holocene hydroclimate variability. This is confirmed by a significant positive correlation of our BR δ18O TR record with a stalagmite δ18O record from Klang cave, southern Thailand (r = 0.303, p < 0.01). In addition, a REDFIT spectral analysis revealed the existence of multidecadal (26.9-year) and interannual (5.6, 3.4 and 2.8-year) cycles, which may potentially be the fingerprints of climate forcing mechanisms impacting Thailand monsoon precipitation, such as the Pacific Decadal Oscillation (PDO) and the El Niño-Southern Oscillation (ENSO). [ABSTRACT FROM AUTHOR]

In semi-arid regions of the world, knowledge about the long-term hydroclimate variability is essential to analyze and evaluate the impact of current climate change on ecosystems. We present the first tree-ring δ18O based hydroclimatic reconstruction for northern semi-arid Iran spanning the period 1515–2015. A highly significant correlation between tree-ring δ18O variations of juniper trees and spring (April–June) precipitation reveals a major influence of spring water availability during the early growing season. The driest period of the past 501 years occurred in the 16th century while the 18th century was the wettest, during which the overall highest frequency of wet year events occurred. A gradual decline in spring precipitation is evident from the beginning of the 19th century, pointing to even drier climate conditions. The analysis of dry/wet events indicates that the frequency of years with relatively dry spring increased over the last three centuries, while the number of wet events decreased. Our findings are in accordance with historical Persian disaster records (e.g., the severe droughts of 1870–1872, 1917–1919; severe flooding of 1867, the 1930s, and 1950). Correlation analyses between the reconstruction and different atmospheric circulation indices revealed no significant influence of large-scale drivers on spring precipitation in northern Iran. [ABSTRACT FROM AUTHOR]

The Himalayan region has already witnessed profound climate changes detectable in the cryosphere and the hydrological cycle, already resulting in drastic socio-economic impacts. We developed a 619-yea-long tree-ring-width chronology from the central Nepal Himalaya, spanning the period 1399–2017 CE. However, due to low replication of the early part of the chronology, only the section after 1600 CE was used for climate reconstruction. Proxy climate relationships indicate that temperature conditions during spring (March–May) are the main forcing factor for tree growth of Tsuga dumosa at the study site. We developed a robust climate reconstruction model and reconstructed spring temperatures for the period 1600–2017 CE. Our reconstruction showed cooler conditions during 1658–1681 CE, 1705–1722 CE, 1753–1773 CE, 1796–1874 CE, 1900–1936 CE, and 1973 CE. Periods with comparably warmer conditions occurred in 1600–1625 CE, 1633–1657 CE, 1682–1704 CE, 1740–1752 CE, 1779–1795 CE, 1936–1945 CE, 1956–1972 CE, and at the beginning of the 21st century. Tropical volcanic eruptions showed only a sporadic impact on the reconstructed temperature. Also, no consistent temperature trend was evident since 1600 CE. Our temperature reconstruction showed positive teleconnections with March–May averaged gridded temperature data for far west Nepal and adjacent areas in Northwest India and on the Southwest Tibetan plateau. We found spectral periodicities of 2.75–4 and 40–65 years frequencies in our temperature reconstruction, indicating that past climate variability in central Nepal might have been influenced by large-scale climate modes, like the Atlantic Multi-decadal Oscillation, the North Atlantic Oscillation, and the El Niño-Southern Oscillation. [ABSTRACT FROM AUTHOR]

Key message: Intra-annual oxygen isotope patterns of tree-ring cellulose fromPinus nigrasubsp.laricioandPinus pinasteralong an elevation gradient can be divided into four distinct patterns ((1) high values in the beginning of the tree ring, declining trend afterwards; (2) low values in the beginning, increasing trend afterwards; (3) high values in the middle of the tree ring; (4) declining trend over the whole tree ring). These patterns reflect the dependency on local site conditions and different water sources. Context: Intra-annual oxygen isotope chronologies from tree-ring cellulose can serve as a proxy for past climate conditions at inter- or even intra-seasonal resolution. Aims: We explore the potential of these chronologies from pine trees (Pinus nigra J.F. Arn subsp. laricio (Poiret) Maire var Corsicana Hyl. and Pinus pinaster Aiton) growing on the Mediterranean island of Corsica, France, along an elevation gradient ranging from sea level to 1600 m asl. Methods: We developed high-resolution intra-annual oxygen isotope chronologies from tree-ring cellulose of eight trees from five sites along the elevation gradient. The analysis period covers the decade 2007–2016 for seven trees and the period 1987–2016 for one tree, respectively. Results: The chronologies show a high variability between trees, sites, and years. We identified four different intra-annual oxygen isotope patterns which reflect the dependency of tree growth on different water sources (precipitation during the growing season vs. deeper soil water reservoirs) and climate conditions during the growth season. Trees at coastal sites have access to groundwater, while trees growing in high elevations mostly depend on precipitation during the growth season as water source. Conclusion: The different patterns can be attributed to the use of different water sources. The intra-annual chronology covering 30 years indicates an increasing frequency of dry-warm summers after 2007. [ABSTRACT FROM AUTHOR]

To develop multi-century stable isotope chronologies from tree rings, pooling techniques are applied to reduce laboratory costs and time. However, pooling of wood samples from different trees may have adverse effects on the signal amplitude in the final isotope chronology. We tested different pooling approaches to identify the method that is most cost-efficient, without compromising the ability of the final chronology to reflect long-term climate variability as well as climatic extreme years. As test material, we used δ18O data from juniper trees (Juniperus polycarpus) from Northern Iran. We compared inter-tree and shifted 5-year blocks serial pooling of stable isotope series from 5 individual trees and addition of one single series to a shifted serial pooled chronology. The inter-tree pooled chronology showed the strongest climate sensitivity and most synchronous δ18O variations with the individual tree ring analyses, while the shifted block chronologies showed a marked decline in high-frequency signals and no correlations with climate variables of the growth year. Combinations of block-pooled and single isotope series compensated the high-frequency decline but added tree-individual climatic signals. Therefore, we recommend pooling calendar synchronous tree rings from individual trees as a viable alternative to individual-tree isotope measurements for robust paleoclimate reconstructions. [ABSTRACT FROM AUTHOR]

Tree-rings are recorders of environmental signals and are therefore often used to reconstruct past environmental conditions. In this paper, we present four annually resolved, multi-centennial tree-ring isotope series from the southeastern Tibetan plateau. The investigation site, where juniper and spruce trees jointly occur, is one of the highest known tree-stands in the world. Tree ring cellulose oxygen (δ18O) and carbon (δ13C) isotopes were analyzed for a common period of 1685–2007 AD to investigate climate–isotope relationships. Therefore, various climate parameters from a local meteorological station and from the CRU 4.02 dataset were used. Tree-ring δ18O of both species revealed highly significant sensitivities with a high degree of coherence to hydroclimate variables during the growing season. The obtained δ18O–climate relationships can even be retained using a species mean. In contrast, the individual δ13C series indicated a weaker and non-uniform response to the tested variables. Underlying species-specific responses and adaptations to the long-term trend in atmospheric CO2 bias even after a trend correction identified dominant environmental factors triggering the tree-ring δ13C at our site. However, analysis of individual intrinsic water-use efficiency in juniper and spruce trees indicated a species-specific adaptation strategy to climate change. [ABSTRACT FROM AUTHOR]

Considerable progress has been made in dendroclimatological research in China during the period 2000–2017, including a significant increase in the spatial coverage of tree-ring chronologies developed for paleoclimatic research. New tree-ring sampling sites have been established across the Tibetan Plateau, as well as the northeastern and sub-tropical eastern parts of China. Most of the studies use coniferous trees, although different plant functional types (e.g., broadleaf species and shrubs) have also been increasingly investigated. Tree-ring chronologies longer than 600 years, however, are mostly found on the Tibetan Plateau, with the longest one extending back to 2637 BCE (before Common Era). Most tree-ring records in the eastern parts of China are <400 years long. Tree-ring width is the most commonly studied parameter, although stable isotope ratios and wood density data have also been obtained for specific sites. Stable oxygen isotope data frequently shares a common hydroclimate signal, whereas the climate or environmental signals remain inconsistent for the few available stable carbon isotope records. In general, tree-ring width-based temperature reconstructions originate from higher elevation sites (i.e., treeline) compared to hydroclimate reconstructions. Precipitation or drought reconstructions are mainly obtained from regions with an annual precipitation of <800 mm. Most of the tree-ring reconstructions are based on individual site or local-scale chronologies, although a limited number of regional-scale and field reconstructions have been produced. The most prominent identified characteristics of the recent advances in dendroclimatological research for China have manifested in aspects such as an expanded network of sampling sites, improved climate reconstruction methodology, and improved uncertainty estimations in the latter. Furthermore, the traditional statistical-based tree growth–climate relationships have been supplemented by monitoring and modeling approaches. Based on the progress from 2000 to 2017, and on the research potential of the country in this field, we expect additional widening of the dendroclimatological investigations in China during the coming years. [ABSTRACT FROM AUTHOR]

Stable isotope ratios in tree rings are increasingly used as palaeoclimatic archive and ecophysiological indicator. We used cross-dated tree-ring series from different tree functional types, i.e. the evergreen conifer Juniperus polycarpus and the deciduous broadleaved Quercus macranthera . The samples were collected from Chaharbagh Gorgon forest in northern Iran, where oaks and junipers grow on north-facing and south-facing slopes, respectively. We extracted α-cellulose from the whole wood of annually separated tree rings and evaluated their potential for palaeoclimate reconstructions by examining the relationships between variations of δ 13 C in tree-ring cellulose and climate parameters. Based on tree-ring δ 13 C, we calculated intrinsic water use efficiency (iWUE) and evaluated changes in water availability at the study site over the past 50 years. We found significant negative relationships between tree-ring δ 13 C values in oak and juniper and precipitation in April and spring (only in junipers), while no significant correlations of tree-ring δ 13 C with temperature occurred. A strong negative relationship between tree-ring δ 13 C and summer Palmer Drought Severity Index (PDSI) was found at the drier site, indicating that juniper growing on south-facing slopes is a better indicator of drought stress in semiarid environments. A continuous increase in iWUE in both species was observed. δ 13 C variations in both species reflect the combined influence of climate and local site conditions. The interplay between climatic conditions and species behavior determines the inter-annual δ 13 C patterns of oak and juniper trees. Due to its more enriched mean δ 13 C (i.e., less negative average δ 13 C) and its higher climatic sensitivity, juniper is a more suitable proxy for paleoclimatic reconstructions in northern Iran. [ABSTRACT FROM AUTHOR]

This study investigates the dendroclimatic potential of tree species in a tropical dry forest in southern Ecuador. From 10 selected tree species, Bursera graveolens and Maclura tinctoria exhibited distinct annual and cross-datable tree-rings. It was possible to synchronize individual tree-ring series and to establish two tree-ring chronologies of 203 and 87 years length, respectively. The characteristic ENSO frequency band is reflected in wavelet power spectra of both chronologies. Both species show a strong correlation between ring width and precipitation of the wet season (January–May). Strong El Niño events (1972, 1983 and 1998) lead to strong growth responses in the tree-ring chronologies, whereas ‘normal’ ENSO events do not trigger long-lasting growth responses. The first ring-width based wet-season precipitation reconstruction for the past 103 years was developed. Statistical and spatial correlation analysis verified the skills of the reconstructed precipitation which captures a great part of the Rainfall Index over the land area of Ecuador and the equatorial Pacific. Furthermore, teleconnections with central Pacific precipitation and SST patterns were found. [ABSTRACT FROM AUTHOR]

• Tree growth in the Karnali river catchment was sensitive to moisture availability. • March–July streamflow was reconstructed for Karnali River Basin since 1628 CE. • An increasing frequency of extreme events was found during the recent decades. • Streamflow variability of the Karnali river is mainly linked with ENSO and PDO. The Karnali River is one of the major transboundary rivers of the Nepalese central Himalaya and a major tributary of the Ganges River. In order to investigate regional historical hydroclimate variability, we compiled eleven tree ring-width chronologies based on 354 exactly dated tree cores from five coniferous species for the Karnali River catchment. The chronologies were moisture-sensitive and the composite chronology was significantly correlated with spring-to-early summer (March–July) (R = 0.67, P < 0.001) discharge at the Chisapani gauging station. The robust calibration (R2 = 0.45, 1962–2010) enabled us to reconstruct March–July streamflow variability of Karnali River Basin (KRB) over the past four centuries. The streamflow reconstruction showed prolonged pluvial periods during 1650–1661, 1711–1718, 1723–1731, 1824–1831, 1877–1889, 1924–1931, and 1971–1981, while prolonged low-flow periods occurred during 1639–1649, 1689–1710, 1753–1769, 1777–1784, 1803–1823, 1867–1876, 1942–1959, and 1963–1970. Our reconstructed March–July streamflow series correlated positively with the seasonally averaged drought index and precipitation in the central-west Himalayan region and vicinities. The streamflow reconstruction revealed an increasing frequency of extreme low-flow and pluvial events in the central-west Himalayan region, especially during the past century. We found short (2.1–3.3, 6.2–6.3, and 8.5–8.7 years) to medium (12.2–12.5 years) periodicities in the reconstructed streamflow series, implying teleconnections with broad-scale climate modes like the El Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Our Karnali River streamflow reconstruction represents an update of regional hydroclimate variability, which may serve as a useful reference for water resource management and appropriate water-use policies in the context of current and future climate change. [ABSTRACT FROM AUTHOR]

For the mechanistic understanding of hydroclimate variability, stable oxygen isotopic ratios (δ 18 O) of tree-ring α-cellulose can play a key role in paleoclimatic research. On the north-east Tibetan Plateau (TP), a region particularly sensitive to climate change, there exists a distinct lack of δ 18 O research in tree-ring archives. The few currently existing tree-ring δ 18 O chronologies were obtained by pooling the wood material from the same year from different trees prior to preparation and analysis. Although this method is time and cost efficient, it might impede the analysis of changes within the internal variability of oxygen isotope signals and a deeper understanding of the resulting climate reconstruction. We selected five Qilian juniper ( Sabina przewalskii Kom .) trees covering the period 1951–2011 on the north-east TP to investigate the climate signals contained in stable oxygen isotopic composition records obtained using single tree analysis. Although the inter-series correlation between the five individual δ 18 O series indicates a highly significant relationship (mean r = 0.59, n = 59, p = 0.01), the five individual δ 18 O series show significantly differently mean values. We found significant negative correlations between drought/hydroclimatically triggered climate parameters (PDSI, precipitation) and each of the individual δ 18 O series. Spatial correlation maps indicate negative correlation of tree-ring δ 18 O and Indian Ocean sea surface temperatures, and inverse correlation patters of moisture conditions on the northern and southern TP. Our results provide a reference for future research on stable oxygen isotope/climate signals in the species S. przewalskii Kom .. [ABSTRACT FROM AUTHOR]

We present a new multi-parameter dataset from Corsican black pine growing on the island of Corsica in the Western Mediterranean basin covering the period AD 1410–2008. Wood parameters measured include tree-ring width, latewood width, earlywood width, cell lumen area, cell width, cell wall thickness, modelled wood density, as well as stable carbon and oxygen isotopes. We evaluated the relationships between different parameters and determined the value of the dataset for climate reconstructions. Correlation analyses revealed that carbon isotope ratios are influenced by cell parameters determining cell size, whereas oxygen isotope ratios are influenced by cell parameters determining the amount of transportable water in the xylem. A summer (June to August) precipitation reconstruction dating back to AD 1185 was established based on tree-ring width. No long-term trends or pronounced periods with extreme high/low precipitation are recorded in our reconstruction, indicating relatively stable moisture conditions over the entire time period. By comparing the precipitation reconstruction with a summer temperature reconstruction derived from the carbon isotope chronologies, we identified summers with extreme climate conditions, i.e. warm-dry, warm-wet, cold-dry and cold-wet. Extreme climate conditions during summer months were found to influence cell parameter characteristics. Cold-wet summers promote the production of broad latewood composed of wide and thin-walled tracheids, while warm-wet summers promote the production of latewood with small thick-walled cells. The presented dataset emphasizes the potential of multi-parameter wood analysis from one tree species over long time scales. [ABSTRACT FROM AUTHOR]

There are knowledge gaps in the long-term changes in Indian summer monsoon rainfall (ISMR, June–September) behaviour, which affects the livelihood of large population in the Indian subcontinent. To better understand ISMR variability, we reconstructed June–July rainfall for the period 1743–2015 CE from Dingad valley, Uttarakhand, central Himalaya using δ18O variations in tree rings. For this, regional mean tree-ring isotope chronology, prepared by merging δ18O chronologies of two conifer (Abies pindrow (Royle ex D.Don) Royle and Picea smithiana (Wall.) Boiss) and one broadleaf deciduous species (Aesculus indica (Wall. ex Camb.) Hook), was used. The reconstructed rainfall series revealed significant correlations with the observational monsoon records from different regions of India. The most conspicuous feature in our reconstructed series is a decreasing rainfall trend since 1743 CE with the driest period in the late 20th and early 21st centuries, which is consistent with other monsoon rainfall proxies from a large part of the south Asian monsoon region (India, Nepal, Bhutan, Myanmar and Tibet Plateau). Consistency of reconstructed series with instrumental records and proxies from different regions revealed the capture of regional scale rainfall features in our data testifying its utility in understanding ISMR variability in long-term perspective. • First 273-years long (1743–-2015 CE) June–July rainfall for the Dingad valley, Uttarakhand, central Himalaya, India using a regional mean isotope tree-ring chronology prepared by averaging species-specific 18O of two conifer (Abies pindrow and Picea smithiana) and one broadleaf deciduous species (Aesculus indica). • The rainfall reconstruction revealed significant correlations with instrumental monsoon records from different regions of India validating the reliability of the dataset in understanding Indian Summer Monsoon Rainfall behaviour for larger region. • The most conspicuous feature in our reconstruction is a decreasing rainfall trend since 1743 CE with the driest period in the late 20th and early 21st centuries. • The reconstruction is consistent with proxy and instrumental records from different regions further underscore the utility in understanding the Indian summer monsoon variability in a long-term context. [ABSTRACT FROM AUTHOR]

High-resolution palaeoclimate proxy records have been lacking for the subtropical region of southwest China. To gain insights into hydroclimate variability in central Yunnan Province, we constructed a tree ring-width chronology of Tsuga dumosa from the Wuliang Mountain area. Correlation analysis shows that moisture availability is predominantly the limiting factor on radial growth, particularly during the spring-early summer season. Using a well-calibrated regression model (R2 = 0.36, p < 0.001), we reconstructed the March–June Standardized Precipitation-Evapotranspiration Index (SPEI) for the period from 1826 to 2020 CE. Eleven extreme drought years (1860, 1897, 1958, 1960, 1979, 1984, 1987, 2006, 2010, 2013, and 2019) were identified, with most of them confirmed by historical evidence. The reconstruction series shows inter-annual to inter-decadal variations and an increasing occurrence of severe dry or wet events in the recent past, particularly during the last 50 years. Our drought reconstruction series shows high frequency cycle of 2–8 years. Spatial correlations indicate that our drought reconstruction captures hydrological signals over a larger area. In line with this, the reconstructed dry periods exhibit broad consistency with other tree-ring based drought reconstructions conducted in nearby regions. Our findings demonstrate the potential of tree-ring proxies for hydroclimate reconstruction in the subtropical areas of southwest China and provide crucial information for evaluating long-term climate change in this region. • Radial growth of T. dumosa in central Yunnan is mainly limited by spring-early summer moisture availability. • The two-century SPEI reconstruction identified eleven extreme drought years that align with historical records. • There has been a notable increase in the occurrence of severe dry or wet events in recent decades. [ABSTRACT FROM AUTHOR]