Tree-ring Chronologies Research Articles

Reconstructing a Fine Resolution Landscape of Annual Gross Primary Product (1895–2013) with Tree-Ring Indices

Low carbon management and policies should refer to local long-term inter-annual carbon uptake. However, most previous research has only focused on the quantity and spatial distribution of gross primary product (GPP) for the past 50 years because most satellite launches, the main GPP data source, were no earlier than 1980. We identified a close relationship between the tree-ring index (TRI) and vegetation carbon dioxide uptake (as measured by GPP) and then developed a nested TRI-GPP model to reconstruct spatially explicit GPP values since 1895 from seven tree-ring chronologies. The model performance in both phases was acceptable: We chose general regression neural network regression and random forest regression in Phase 1 (1895–1937) and Phase 2 (1938–1985). With the simulated and real GPP maps, we observed that the GPP for grassland and overall GPP were increasing. The GPP landscape patterns were stable, but in recent years, the GPP’s increasing rate surpassed any other period in the past 130 years. The main local climate driver was the Palmer Drought Severity Index (PDSI), and GPP had a significant positive correlation with PDSI in the growing season (June, July, and August). With the GPP maps derived from the nested TRI-GPP model, we can create fine-scale GPP maps to understand vegetation change and carbon uptake over the past century.

Arctic amplification causes earlier onset of seasonal tree growth in northeastern Siberia

Abstract Although recent warming affects the high-northern latitudes at an unprecedented rate, little is known about its impact on boreal forests because in situ observations from remote ecosystems in Siberia are sparse. Here, we analyze the radial growth and climate sensitivity of 54 Cajander larches (Larix cajanderi Mayr.) from three sites across the northern treeline ecotone within the Omoloy river basin in northeastern Siberia. Three independent tree-ring width chronologies span 279–499 years and exhibit distinct summer temperature signals. These records further reveal evidence for sufficiently earlier onsets of growing seasons since the middle of the 20th century. This phenological shift coincides with rapidly increasing May temperatures and associated earlier snowmelt. Our findings reinforce the importance of high-precision ground measurements from remote regions in Siberia to better understand how warming-induced changes in the functioning and productivity of the boreal forest influence carbon, nutrient, and water cycle dynamics.

Exploring the potential for a 9000-year tree-ring chronology consisting of subfossil oak material from southern Scandinavia

In this study, we present the initial results from a long-term initiative to develop a multi-millennial tree-ring width (TRW) chronology for subfossil oak (Quercus spp.) trees in South Scandinavia. We have constructed 40 TRW chronologies, primarily from oak trunks extracted from peatlands, archaeological sites, drainage ditches, and infrastructure projects, as well as some submerged material. The trees included in these chronologies have been dendrochronologically dated and/or dated by radiocarbon, showing a temporal spread from 6911 ± 246 BCE to 1117 CE. Significant assemblages of trees are found during the periods 6000–4500 BCE, 3500–2600 BCE, 1750–1200 BCE, 900–400 BCE, and 200 BCE–500 CE, with intervening periods exhibiting low sample replication or gaps. The paleoclimatic information extracted from TRW and replication data may vary based on the substrate in which the trees were rooted, geographical locations, and the prevailing climate conditions during their growth. Nevertheless, extending the oak TRW chronologies is crucial because (1) no such long and annually resolved climate records from southern Scandinavia exist, (2) there is a widespread lack of detailed paleoclimatic proxies spanning multi-millennial periods, and (3) it will provide an essential dating tool for wooden archaeological artifacts. This study is the first in a series aimed at refining paleoclimatic and ecological reconstructions in southern Scandinavia. It demonstrates the potential to develop South Scandinavian TRW chronologies covering the last 9000 years, filling a geographical gap in an ecologically sensitive region.

Historical drivers and future streamflow variations of the Kura River in the Western Transcaucasia region of Georgia: Analysis of tree-ring chronologies from 1720 to 2021 CE

In this paper, we conduct a dendrochronological study in the Western Transcaucasia region of Georgia to elucidate the relationship between tree growth and climatic variables (temperature, precipitation, and streamflow) in order to reconstruct the paleohydrology of the Kura River and to assess the impacts of climate change on water resources. We analyzed tree-ring chronologies from 1720 to 2021 CE, and analysis of July–August streamflow revealed five wet phases (1739–1753, 1764–1807, 1811–1831, 1962–1988 and 2000–2019 CE ranging in duration from 11 to 49 years) when streamflow exceeded the long-term mean, and four dry phases (1720–1738, 1832–1881, 1936–1961 and 1989–1999 CE) when streamflow was below average. The most extreme wet and dry years were 1771 and 1851 CE, respectively. Spatial correlation patterns of Kura River reconstructed runoff against sea level pressure (SLP) are negative in the Arctic and positive in mid- to high-latitude Eurasia. The Arctic Oscillation (AO)/North Atlantic Oscillation (NAO), and solar activity are important drivers of hydroclimatic conditions in the Mediterranean region, by modifying the location of high-pressure areas and large-scale atmospheric circulations. Comparison of our Kura streamflow reconstructions and data in the Old World Drought Atlas (OWDA) reveals a moderately positive correlation (0.40) throughout the study period, being strongest over the Southern Caucasus and Eastern Turkey. This validates the drought signals and emphasizes the importance of using multi-proxy approaches, supported by spatially resolved data, to enhance understanding of regional hydroclimatic variability and drought patterns. We additionally conducted future streamflow scenarios, most notably under the high-emission SSP585 scenario, in line with global trends in CMIP6 projections. Our streamflow results indicate a trend towards increasing drought severity, which highlights the need for urgent adaptation and mitigation strategies in water resource management in this region. Ultimately, this study provides valuable information on historical hydroclimatic conditions in the Kura River Basin, which help to develop strategies to mitigate the hydrologic impacts of climate change in the Western Transcaucasia Caucasus region. We further highlight the importance of regional and global teleconnections for understanding regional hydrological dynamics.

Early-successional species show higher tolerance of drought than late-successional species across Europe.

Climate change is exacerbating forest disturbances through more frequent and more intense droughts and fires, undermining their ability to recover from such disturbances. The response of fast-growing early-successional species to drought is poorly understood, despite their key role in ecological succession and their ability to enhance ecosystem resilience. Here, we compared the growth responses to drought events of three early-successional species (silver birch, black poplar, and Scots pine) with that of one late-successional species (European beech) across their natural distribution ranges in Europe. We used tree-ring widths of 6340 trees from 109 forest sites to establish species-specific tree-ring chronologies. We then used multiple linear regressions to analyze which climatic or growth variables (pre-drought growth and growth during drought) best explained the tree responses to drought. Silver birch, Scots pine, and black poplar showed superior drought tolerance, with a slight, non-significant growth reduction under drought, whereas European beech showed a significant decrease in growth. The variables that influenced growth during and after the drought were species-specific. Annual precipitation and growth variables were key predictors of post-drought growth for Scots pine, black poplar, and European beech. Scots pine and silver birch grew better with increasing latitude, i.e., in Northern Europe than in Central Europe, while European beech and black poplar showed more growth at sites with high precipitation during the vegetation and dormant period, respectively. This study provides insights into the drought tolerance of early-successional species and highlights their ability to promote ecological succession and facilitate the transition to drought-resistant, late-successional forest ecosystems.

Introduction of broadleaf tree species can promote the resource use efficiency and gross primary productivity of pure forests.

Long-term pure forest (PF) management and successive planting has result resulted in "low-efficiency artificial forests" in large areas. However, controversy persists over the promoting effect of introduction of broadleaf tree species on production efficiency of PF. This study hypothesised that introduced broadleaf tree species can significantly promote both water-nutrient use efficiency and gross primary productivity (GPP)of PF. Tree ring chronologies, water source, water use efficiency and GPP were analysed in coniferous Cunninghamia lanceolata and broadleaved Phoebe zhennan growing over the past three decades. The introduction of P. zhennan into C. lanceolata plantations resulted in inter-specific competition for water, probably because of the similarity of the main water source of these two tree species. However, C. lanceolata absorbed more water with a higher nutrient level from the 40-60-cm soil layer in mixed forests (MF). Although the co-existing tree species limited the basal area increment and growth rates of C. lanceolata in MF plots, the acquisition of dissolved nutrients from the fertile topsoil layer were enhanced; this increased the water use efficiency and GPP of MF plots. To achieve better ecological benefits and GPP, MFs should be constructed in southern China.

Hydrothermal environments lead to differences in the radial growth response of Pinus tabulaeformis to climate in the monsoon marginal zone, Northwestern China

Regional climatic differences increase the complexity of tree radial growth responses to climate change in the monsoon marginal zones and may alter the carbon sequestration capacity of forests. In this study, we collected cores of Pinus tabulaeformis trees at nine sampling sites across different regions. We analysed the relationship between tree-ring width chronology and climatic factors at different sites using dendroecological methods. We used the tree-ring index to calculate resistance, recovery, and resilience as well as to explore the capacity of radial growth to cope with drought events. The results indicate that (1) Drought was the primary factor limiting tree growth, and tree-ring climate response patterns varied across three regions. Tree growth was sensitive to both temperature and precipitation in the eastern Qilian Mountains, while it was more sensitive to temperature in the Hassan Mountains and more sensitive to precipitation in the Helan Mountains. (2) The tree-ring climate response pattern remained unstable over time, and the relative influence of current climate on tree growth increased. (3) The ecological resilience of trees to extreme events varies across three regions, which could be attributed to regional moisture conditions and the duration of drought. In the context of the management and protection of trees in the study area in the future, more attention should be paid to the elasticity of tree growth after drought events.

Increasing drought frequency in the central Zagros Mountains of western Iran over the past two centuries

The Zagros region in western Iran has experienced prolonged drought, significantly impacting water resource and forest ecosystems over the past few centuries. Understanding historical prolonged drought is crucial for making precise forecasts of shifts in regional drought in the Zagros region. Due to the lack of comprehensive historical records, the use of proxy records is considered a valuable tool for reconstructing past drought variations. We aimed to construct a tree-ring chronology of Juniper (Juniperus polycarpus) in the central Zagros region to comprehend its growth response to climate variables. We cored 25 J. polycarpus trees from the Keygooran forest reserve in western Iran and developed the tree ring chronology (1802–2022) using dplR. The relationships between tree growth and climate variables of monthly mean temperature, precipitation, PDSI (Palmer Drought Severity Index), and SPEI (Standardized Precipitation Evapotranspiration Index) were examined. The analysis revealed a strong positive correlation between tree growth and SPEI March-September of 1990–2018 on a 48-month timescale with a 2-year lag (r = 0.61, p < 0.05) which was included in the transfer model. Consequently, the SPEI-48 March-September was reconstructed for the period 1802–2022. On this reconstruction, several extremely dry years in 1832, 1867, and 1876 and extremely wet years in 1807, 1814, 1838, 1850, 1907, and 1908 years were identified, some of them aligning with historical records in Iran. Furthermore, there was a relationship between SPEI-48 March-September and teleconnection events suggesting that certain drought occurrences in the area were associated with the El Niño-Southern Oscillation (ENSO). Consequently, this reconstruction can serve as a reliable proxy for large-scale drought variability in the Zagros region of western Iran. Moreover, our research underscores the utility of SPEI in reconstructing the history of semi-arid climate conditions.

Late Ming Dynasty weak monsoon induced a harmonized megadrought across north-to-south China

Historians and paleoclimatologists have long studied the connection between ecoclimatic changes and empire growth, transformation, and decline, but striking cases remain rare. Here, we introduce a tree-ring chronology from southern China to reconstruct changes in April-to-November water balance of the middle reaches of the Yangtze River over the last 464 years. The reconstruction supports a quantitative assessment of the spatiotemporal structure of the late Ming megadrought and potential effects on subsequent dynastic transitions. Our results indicate that the late Ming megadrought from 1625 – 1644 CE occurred in both the northern and southern parts of the East Asian monsoon region in China. However, variations in the onset, duration, and magnitude of this event differ between regions. The combination of factors such as Pacific sea surface temperature anomalies, weakened solar activity, and large-scale volcanic eruptions may have contributed to the occurrence of the late Ming megadrought. These factors are also identified as key drivers of interannual to decadal fluctuations in drought in the middle reaches of the Yangtze River. Our reconstruction provides an historical context for the development of adaptive measures to mitigate future drought impacts in the region.

Reconstructing the Temperature and Precipitation Changes in the Northern Part of the Greater Khingan Mountains over the Past 210 Years Using Tree Ring Width Data

In northeastern China, simultaneous reconstruction of temperature and precipitation changes in the same region using tree ring data has not yet been reported, limiting our understanding of the historical climate. Using tree ring samples from the Greater Khingan Mountains, it was established that there are five standardized tree ring width chronologies of Pinus sylvestris var. mongolica at five elevations. Correlation analyses revealed significant relationships between the tree ring chronologies and climate data for multiple months. Specifically, the correlation coefficient between the average minimum temperature from May to July and the composite chronologies of mid–high and mid-elevations was 0.726, whereas that between the total precipitation from August to July and the low-elevation chronology was 0.648 (p &lt; 0.01). Based on these findings, we reconstructed two series: the average minimum temperature from May to July over the past 211 years and the total precipitation from August to July over the past 214 years. The reconstructed sequences revealed changes in the average minimum temperature from 1812 to 2022 and precipitation from 1809 to 2022 in the northern part of the Greater Khingan Mountains. The variances explained by the reconstruction equations were 0.528 and 0.421 (adjusted R-squared: 0.520 and 0.411), with F-test values of 65.896 and 42.850, respectively, exceeding the significance level of 0.01. The reliability of the reconstructed sequences was validated by historical records of meteorological disasters and the reconstruction results in the surrounding area. The reconstructed temperature and precipitation sequences exhibited distinct patterns of temperature fluctuations, dry–wet changes, and periodic oscillations. The region experienced two warm periods (1896–1909 and 2006–2020), two cold periods (1882–1888 and 1961–1987), a wet period (1928–1938), a drought period (1912–1914), and a period prone to severe drought events (1893–1919) during the past 210 years. The temperature series showed periodicities of 2–2.5 years, 3.9 years, 5.2 years, and 68 years, while the precipitation series exhibited periodicities of 2.1 years, 2.5 years, and 2.8 years, possibly related to El Niño–Southern Oscillation (ENSO) events, quasi-biennial oscillation, and Pacific Decadal Oscillation (PDO). Spatial correlation analysis indicated that the reconstructed temperature and precipitation sequences accurately represented the hydrothermal changes in the study area.

Sensitivity of sub-annual grey pine (Pinus sabiniana) stem growth to water supply and demand in central California

Pinus sabiniana (grey pine) is a common associate of Quercus douglasii (blue oak) in the iconic, ecologically-rich, and economically-relevant Mediterranean woodland savannah of California, USA. While there are dozens of Q. douglasii sites in the International Tree-Ring Data Bank, P. sabiniana was conspicuously absent, and little is known about its growth patterns or water relations. Here, we introduce a new tree-ring chronology of P. sabiniana collected in central California and assess climatic drivers of annual and sub-annual growth. Specifically, we examine earlywood, latewood, and total annual ring widths and analyse their relationships with variables related to water supply (precipitation, soil moisture) and water demand (air temperature, potential evaporation rate). Annual and earlywood widths had nearly identical responses to climate, likely because annual widths mostly consisted of earlywood (mean: 88 %). In both cases, growth was strongly and positively associated with water supply and negatively associated with water demand. Soil moisture was, by far, the strongest and most temporally-consistent correlate of P. sabiniana growth: correlations between soil moisture and annual growth were >0.8 for five contiguous 3-month seasons. Other variables were significant, in part, because of their influence on soil moisture. The association between latewood growth and climate was qualitatively similar but weaker and, with the exception of soil moisture, more seasonally localised (precipitation was relevant in winter and early spring and water demand variables were relevant in summer, somewhat later in the season than for total ring width and earlywood). Further, P. sabiniana growth was nearly always more sensitive to soil moisture than growth of either co-located Q. douglasii or P. ponderosa (ponderosa pine) at a neighbouring site, suggesting that it may act as a particularly sensitive harbinger of drought stress in this ecosystem.

Tree-Ring Chronologies from the Upper Treeline in the Russian Altai Mountains Reveal Strong and Stable Summer Temperature Signals

Radial tree growth at high-elevation and high-latitude sites is predominantly controlled by changes in summer temperature. This relationship is, however, expected to weaken under projected global warming, which questions the reliability of tree-ring chronologies for climate reconstructions. Here, we examined the growth–climate response patterns of five tree-ring width (TRW) and maximum latewood density (MXD) chronologies of larch (Larix sibirica) from upper-treeline ecotones in the Altai Mountains, which is a key region for developing millennial-long dendroclimatic records in inner Eurasia. The TRW and MXD chronologies exhibited significant year-to-year coherency within and between the two parameters (p &lt; 0.001). While TRW is mostly influenced by temperature changes during the first half of the growing season from June to July (r = 0.66), MXD is most strongly correlated with May–August temperatures (r = 0.73). All seasonal temperature signals are statistically significant at the 99% confidence level, temporally stable back to 1940 CE, the period with reliable instrumental measurements, and spatially representative for a vast area of inner Eurasia between northeastern Kazakhstan in the west, northern Mongolia in the east, southern Russia in the north and northwestern China in the south. Our findings demonstrate the paleoclimatic potential of TRW and especially MXD chronologies and reject any sign of the ´divergence problem´ at these high-elevation, mid-latitude larch sites.

Methodological constrains of tree-ring stable isotope chronologies

Tree-ring stable isotope (TRSI) chronologies that combine information from living and relict wood have the potential to capture long-term trends that might be missing in traditional tree-ring width and maximum latewood density measurements. Our understanding of the possible effects of different methods to develop TRSI chronologies is, however, still incomplete. Here, we compare and evaluate five such methods applied to three multi-millennial-long oxygen isotope (δ18O) TRSI datasets from central Europe, the European Alps and Japan: (a) raw data, (b) cohort correction, (c) interactive mean correction, (d) outlier correction, and (e) series normalization. We show that the spectral properties preserved in the final TRSI chronologies not only depend on the data used, but also on the techniques applied. Method (a) is particularly prone to outliers if the sample size is low. Method (b) may create artificial steps and trends when single measurement series share similar start dates and/or when end and start dates are systematically skewed. Methods (c) and (d) yield similar results for annually resolved data, yet (d) is more suitable for temporally pooled datasets and less sensitive to potential biological age effects. Method (e) removes any low-frequency signal. Our findings demonstrate the risks and rewards of different TRSI chronology development techniques that must be carefully adapted to both, the data used and the question posed.

Tree-growth synchrony index, an effective indicator of historical climatic extremes

BackgroundTree rings play an important role in reconstructing past climate. Growth differences among individual trees due to microclimatic conditions and local disturbances are averaged in developing tree-ring chronologies. Here, we addressed the problem of averaging by investigating growth synchrony in individual trees. We used tree-ring data of 1046 juniper trees from 32 sites on the Tibetan Plateau and 538 pine trees from 20 sites in the subtropical region of eastern China and calculated the tree-growth synchrony index (TGS).ResultsOur results showed that both the TGS index and tree-ring index could be indicators of interannual variation of climatic factors. The TGS index identified 20% more climatic extremes than tree-ring index over the last 50 years that high synchrony indicates extreme climate forcing in controlling forest growth.ConclusionsThe TGS index can identify extreme climatic events effectively than tree-ring index. This study provides a novel perspective for climate reconstruction, especially in the realm of tree growth response to extreme climate. Our findings contribute to understanding of the spatiotemporal dynamics and the causes of historical climate extremes and provide guidance for protecting trees from climate extremes in the future.

A multi-centennial drought reconstruction from tree-rings reveals a growing threat to Christmas Island’s water resources

Small islands that depend on limited freshwater resources are at significant risk from seasonal drought, which poses a major threat to both their ecosystems and communities. Christmas Island, located in the eastern Indian Ocean, presents an example for which severe drought conditions during the wet season not only affects its freshwater resources but also biodiversity on the island, including the migration pattern of the iconic red crab species. However, short-term instrumental climate records on this island make it hard to quantify drought variability and assess its associated risks. Tree growth is affected by drought via reduced soil moisture, and hydroclimate reconstruction from tree-ring chronologies can therefore provide longer-term information on historical variability of dry and wet periods. Here, we reconstructed the wet season (December-May) self-calibrating Palmer Drought Severity Index (scPDSI) for Christmas Island using 64 remote tree-ring chronologies from Asia, Australia, and New Zealand. scPDSI was reconstructed using the Point-to-Point Regression (PPR) method and compared with regional marine coral proxies for independent verification. The remote tree-ring chronologies explained more than 66 percent of scPDSI variance (R-squared) over the calibration period. The trees identified as significant predictors in the regression model were primarily located in areas affected by the Indo-Pacific climate drivers including the Indian Ocean Dipole (IOD). The reconstructions span 1540 CE to 2000. During the first four centuries of this period, the frequency of extreme (5th percentile) droughts and pluvial events rarely exceeded one event per 13 years. In contrast, the frequency of both extremes experienced an unprecedented increase during the 20th century, and with a notable shift towards dry conditions. These findings highlight a significant shift towards more frequent and severe dry conditions during the wet season on Christmas Island, posing a challenge to water resource management and potentially threatening the island's ecosystem and services to the community.

New methods in dendroarchaeology: possibilities for studying charcoals from archaeological sites (the case of the Kara-Dyt II site, Republic of Tyva)

Traditionally, charcoal from archaeological sites was considered an unsuitable material for dendrochronological dating. The authors examined 23 coal samples from the Kara-Dyt II site (Republic of Tyva, Russia). An analysis of existing solutions for sample preparation of such material showed their low speed and efficiency. This article uses the approach developed by the authors, which allows for quick and high-quality sample preparation of a large number of charcoals with minimal labour costs. As a result, it was possible to construct a 138-year tree-ring chronology using archaeological charcoal. Further work in this direction will make it possible to solve the problem of constructing a long-term tree-ring chronology in the arid zone of South Siberia. This chronology provides a unique tool for determining the calendar age of wood from numerous burial mounds in Tuva and for an in-depth study of the relationship between climate and society over the past two millennia.

The effect of climate change on the radial growth of Pinus sylvestris l. and Quercus robur l. in the stands of Kharkiv green zone

Purpose. To identify the characteristics of the reaction of the radial growth of Scots pine (Pinus Sylvestris L.) and Scots oak (Quercus robur L.) to climate change in the forest-steppe zone of Ukraine. Methods. Dendrochronological, dendroclimatological, and statistical methods are applied. COFECHA and ARSTAN programs were used. Results. The study was conducted in 100-year-old stands of English oak and Scots pine in the Southern Forestry (Left-bank Forest-steppe). The reaction of the radial growth of trees to climate changes was compared for 1960-1987 and 1988-2016. For the dendroclimatic analysis, the de Martonne hydrothermal indices, the Selyaninov hydrothermal coefficient, the forest aridity index, and the O1 hydrothermal coefficient were used. Relative humidity indicators, which are derived from temperature and precipitation, were also used. It was found that in the second period, the sensitivity of the reaction of the radial growth of trees to climate variations increased, which indicates a certain weakening of the stands due to the increase in temperature. Dendroclimatic analysis of Pinus sylvestris L. and Quercus robur L. showed that when comparing the response of the radial growth of trees to climate variations in 1960-1987 and 1988-2016, the condition of both pine and oak weakened, as evidenced by an increase in significant coefficients correlations between growth indices and climatic factors. Conclusions. Pine was found to be more sensitive to climate change compared to oak. At the same time, these species of these trees at this stage were able to adapt to climate change, as evidenced by tree-ring chronologies, which show stable growth during 2010-2016.

Hydroclimate variability in the Tropical Andes recorded by δ18O isotopes from a new network of Polylepis tarapacana tree-rings

Stable oxygen isotopes records (δ18O) in tree-rings are commonly used to assess the response of trees to environmental variability being a valuable tool for studying past climate at different temporal and spatial scales. This is particularly relevant in semi-arid regions like the southern Tropical Andes, where ongoing environmental changes coincide with a rapidly increasing demand for hydrological resources, presenting a challenge for ecosystem dynamics and water resource management. In this study, we aim to determine the main spatio-temporal variability of a new network of δ18O Polylepis tarapacana chronologies during the last century, and their relationships with hydroclimate and tropical circulation at local to subcontinental scales throughout the Tropical Andes. For this purpose, we develop six δ18O P. tarapacana tree-ring chronologies across a 450 km latitudinal moisture gradient in the southern Tropical Andes adjacent to the Atacama Desert, covering the period 1900–2007. Results show a clear latitudinal gradient in the δ18O values across the network and significant relationships are observed with other δ18O tree-ring chronologies in Tropical South America, demonstrating clear regional climate influences at a subcontinental scale. A principal component analysis of the δ18O tree-ring chronologies demonstrate a strong regional environmental signal contained in the network, exhibiting a main temporal pattern (PC1 δ18O) that explains 63% of the total variance during the period 1900–2007. Comparisons between PC1 δ18O and environmental variables showed significant negative relationships with precipitation and soil moisture, and positive relationships with temperature and vapor pressure deficit (VPD) during summer when the South American monsoon occurs. The main δ18O tree-ring network signal clearly records tropical atmospheric and circulation patterns across South America. The easterly wind flux conditions from the Amazon basin favor lower δ18O values, and the PC1 δ18O exhibit significant positive correlations with VPD across the entire Tropical Andes and the northern portion of the Amazon basin, and as well as outgoing longwave radiation across the southern Tropical Andes and part of the Amazon basin. The close relationships between the regional signals from our δ18O tree-ring network with the previously mentioned parameters, highlight the potential to develop future hydroclimatic-related reconstructions with these δ18O records to assess climate variability and change across the Tropical Andes.

Reconstruction of NDVI based on Larix gmelinii tree-rings during June–September 1759–2021

Investigating the long-term dynamics in the canopy proves to be difficult due to the short observational records of the normalized difference vegetation index (NDVI). To explore the linkage between tree growth, NDVI dynamics and large-scale atmospheric circulation in the Greater Khingan Mountain, Northeast China, we established a chronology of Larix gmelinii tree ring width at three elevations (870–920 m, 1,100–1,150 m and 1,270–1,320 m) in the northern foothills of the mountain range. We then calculated the correlations between the tree ring chronologies and NDVI and climate factors, and reconstructed the NDVI time series from June to September 1759–2021 in the region based on the middle-elevation tree ring chronology. The results identify the positive effect of temperature (r = 0.56, p &amp;lt; 0.01) and the negative effect of precipitation (r = −0.44, p &amp;lt; 0.01) in the growing season as the main influencing factors of NDVI for the study period (1981–2019). The 11-year moving average of the reconstructed NDVI series reveals two periods of high canopy vigor (1898–1926 and 2009–2013) and three periods of low canopy vigor (1860–1962, 1882–1888 and 1968–1977) in the last 263 years. These periods correspond to drought events recorded in the historical literature. Wavelet analysis shows that the reconstructed sequences exhibited 11–13, 23–25, and 39–42 years period variations. Integrating this with spatial correlation analysis reveals that tree growth in the Mangui region was impacted by the combined effect of the North Pacific Decadal Oscillation and the North Atlantic Multidecadal Oscillation. The results of this paper provide a reference for the study of vegetation change patterns in the northern foothills of the Greater Khingan Mountains.

Precipitation Reconstruction Using Tree-Ring Chronologies from Jordan and the Eastern Mediterranean Region

Precipitation Reconstruction Using Tree-Ring Chronologies from Jordan and the Eastern Mediterranean Region