Tree-ring Width Series Research Articles

Topography and age mediate the growth responses of Smith fir to climate warming in the southeastern Tibetan Plateau.

The Tibetan Plateau holds some of the world's highest undisturbed natural treelines and timberlines. Such extreme environments constitute potentially valuable monitoring sites of the effects of climate warming on high-elevation forests. Here, we analyze a network of 21 Smith fir forests situated in the Sygera Mountains, southeastern Tibetan Plateau, using tree-ring width (TRW) and basal area increment (BAI) chronologies. Sampled sites encompassed a wide elevation gradient, from 3600 to 4400m, including some treeline sites and diverse aspects and tree ages. In comparison with TRW series, BAI series better capture the long-term warming signal. Previous November and current April and summer temperatures are the dominant climatic factors controlling Smith fir radial growth. The mean inter-series correlations of TRW increased upwards, but the forest limit presented the highest potential to reconstruct past temperature variability. Moreover, the growth responses of young trees were less stable than those of trees older than 100years. Climate warming is accelerating radial growth of Smith fir forest subjected to mesic conditions. Collectively, these findings confirm that the effects of site elevation and tree age should be considered when quantifying climate-growth relationships. The type of tree-ring data (BAI vs. TRW) is also relevant since BAI indices seem to be a better climatic proxy of low-frequency temperature signals than TRW indices. Therefore, site (e.g., elevation) and tree (e.g., age) features should be considered to properly evaluate the effects of climate warming on growth of high-elevation forests.

Climatic forcing of xylem formation in Qilian juniper on the northeastern Tibetan Plateau

Cambial activity of ~100-year-old Qilian juniper trees initiated before the middle of May at an elevation of 3200 m a.s.l.; June and July were the main stem radial increment period. Around the middle of August, all xylem cell differentiation periods are completed. Precipitation or relative humidity is the main limiting factor for tree radial growth on the northeastern Tibetan Plateau. Previous studies have found that annual tree-ring width series of Qilian juniper (Sabina przewalskii Kom.) in the northeastern Tibetan Plateau (TP) are mostly moisture controlled, irrespective of site elevation. Knowing precisely the cambial growth dynamics during a vegetation period can lead to a better understanding of the climatic factors driving regional tree growth patterns. We observed wood formation with micro-cores taken at weekly intervals from late April to early October 2013, and monitored daily stem radial changes with high-resolution electronic point dendrometers in 30-min intervals. Dormant cambium contained 5–6 cell layers in the cambium zone. Cambial activity initiated before the middle of May in all the monitored trees. About three quarters of the total cell production or radial growth formed during June and July. Lignification of secondary walls of new xylem cells continued from end of May to middle of August. After the middle of August, the cambium entered into the inactive period. Dendrometer measurements confirmed that June and July were the main stem radial increment period. Nonparametric Kendall’s Tau correlations indicate that daily relative humidity and precipitation significantly influence stem growth in May. No obvious relationships were detected in June. In July, significant negative influences of maximum temperature and positive effects of relative humidity prevailed. Overall, growing season precipitation or associated relative humidity is the limiting factor for tree stem radial increments on the intra-annual scale. Our results present a thorough understanding of Qilian juniper xylogenesis and its climate forcing within the whole growing season on the northeastern TP.

A Millennial Summer Temperature Reconstruction for the Eastern Tibetan Plateau from Tree-Ring Width*

Abstract Although tree-ring-width-based temperature reconstructions of centennial-to-millennial length have previously been published for many parts of the eastern Tibetan Plateau (ETP), a millennium-long regional-scale composite reconstruction with annual resolution has so far been lacking. Here, the authors present a reconstruction of June–August (JJA) temperature variability over the ETP for the period AD 1000–2005 using a nested composite-plus-scale (CPS) approach to 12 temperature-sensitive tree-ring width chronologies, including 946 individual tree-ring width series. The composite reconstruction reveals warm episodes occurring during much of the sixteenth, nineteenth, and twentieth centuries and cold episodes during much of the eleventh, seventeenth, and eighteenth centuries. The period AD 1996–2005 is likely the warmest decade in the context of the past millennium. The authors explore the influence of possible forcings, finding only a weak direct relationship of temperature changes over the ETP with solar forcing at multidecadal time scales but a robust in-phase relationship with the Atlantic multidecadal oscillation (AMO) during the past millennium. This suggests that the AMO may play an important role in controlling summer temperature variability over the ETP at multidecadal time scales. A comparison with temperature reconstructions from the higher latitudes of East Asia, central-eastern China, and the whole of the Northern Hemisphere shows that the cold eleventh century and the warm nineteenth century prevailing over ETP are somewhat unique, suggesting regional specific characteristics of the temperature variability in this region. This result highlights the need to further increase the number of millennium-long, high-resolution temperature records from East Asia.

Reconstructing Evaporation From Pine Tree Rings In Northern Mexico

Here we reconstructed evaporation using tree-ring width variability. Drought variability and its effects on forest growth have been mainly characterized by changes in precipitation and temperatures, whereas atmospheric drought and evaporation rates have been little investigated. The area of study corresponds to northern Mexico, a region where water resources are increasingly limited. We used correlation analyses to identify the months in which evaporation is most strongly related to tree-ring width series. Then, we built a linear regression model to predict seasonal winter-to-spring evaporation as a function of ring-width indices. Correlation analyses showed that the radial growth of P. cooperi decreased in response to reduced water availability and increased evaporation during the winter prior to the growing season, and also during spring and the early summer of the year of tree-ring formation. Pine growth mainly benefitted from wet and cool conditions from winter to early spring. Linear regression models used in reconstruction were statistically robust and allowed reconstructing January-to-April evaporation for the period 1900–2010. Our study contributes to a better understanding of historical changes in evaporation in northern Mexico and, most importantly, it also emphasizes how atmospheric moisture demand is linked to tree growth.

Tree-ring based reconstruction of Río Bermejo streamflow in subtropical South America

Summary Precipitation on the subtropical Andes in northwestern Argentina is the main source of freshwater to rivers, which provide water for consumption, hydroelectric generation and irrigation of agricultural fields. Regional streamflow records for the past 60 years indicate a period of enhanced inter-annual and inter-decadal variability during recent decades. Here we present a long-term perspective of streamflow variations for Rio Bermejo, a major river in the subtropics of Argentina–Bolivia. This streamflow reconstruction covers the period 1680–2001 and was performed using principal component regression models based on precipitation sensitive tree-ring width series. Composite tree-ring chronologies from Juglans australis , Cedrela lilloi and Schinopsis lorentzii were used as predictors to reconstruct the May–October (dry season) streamflow variations. Monthly instrumental streamflow records were used to assess the temporal relationship between climatic data and tree-ring records. The regression model explains 52% of the variance of May–October Bermejo discharge ( R 2 adj = 0.499) over the period 1941–1992. Analyses of the frequency, intensity and duration of pluvials and droughts indicates a sustained increase in streamflow since the 1960s, which is exceptional since 1680. Pearson’s correlation coefficients between Rio Bermejo records against gridded interpolated precipitation and outgoing longwave radiation indicate that the South American monsoon is the main source of regional precipitation and the consequent discharge of subtropical rivers in northern Argentina. Long-term streamflow reconstructions in subtropical South America contribute to our understanding of past and present climate variations and the related large-scale atmospheric features that drive these variations.

Aleppo pine vulnerability to climate stress is independent of site productivity of forest stands in southeastern Spain

Clim ate is the main driver of Aleppo pine radial growth variability irrespective of site pro ductivity, with the climate effects on tree growth more limiting from 1970 onwards. Forest management adaptation to climate change requires identifying the previously most vulnerable stands and the possible climate impacts on forests. This study evaluates whether site index, as an indicator of forest productivity, is related to climate–growth responses and assesses the way in which local site factors modulate climate–tree growth relationships. Tree-ring width series and soil characteristics were obtained from six Pinus halepensis stands with different site indices and similar climate. Dendrochronological methods were used to compare tree climate–growth responses among sites and to study temporal trends in inter-annual growth variability and climate–growth relationships (before and after 1970). The influence of topographic and soil features on tree growth was assessed by means of partial least squares. Stands with low site indices tended to present higher mean sensitivities and greater percentages of missing rings, this relation being modulated mainly by clay percentage and nutrient status in soil. Climate is the major Aleppo pine radial growth driver in the study area with similar growth–climate relationship among sites. Radial growth was mainly influenced by spring temperature and precipitation and previous autumn–winter precipitation. This relationship was stronger after 1970 than before this year, showing also a 2-month advancement of the most influential climate variables after 1970, from May to March. These results and the increasing temporal trend found in mean sensitivity after 1970 highlight the vulnerability of these stands to climate change. Site index was not found to be directly related to stand vulnerability, although local site factors modulate in part the tree-growth response.

Dendroclimatic signals of pedunculate oak (Quercus robur L.) in Estonia

This study investigates the climate impact on the radial increment of pedunculate oak (Quercus robur L.) in Estonia at the species’ northern distribution limit. Tree-ring width series of 162 living oaks were compiled into three regional chronologies—western (1646–2008), northeastern (1736–2011), and southeastern Estonia (1912–2011). Although these regional growth patterns are similar to each other and even to the growth patterns in adjacent regions, spatial differences in growth responses to climate were established. Thus, oaks growing on shallow soil in western Estonia are positively influenced by summer (June–August) precipitation, and oaks on the deeper soil in northeastern Estonia are favoured by June temperature, while oaks in the southeastern part of the country depend on both July precipitation and temperature. These relationships are pronounced especially in pointer years. However, due to the impact of regional weather fluctuations on tree growth, there is a lack of correspondence between the local and the pan-European pointer years. In addition, our research presents the first tree-ring-based palaeoclimatic reconstruction for the country. Although the created model has relatively low predictive skill describing less than a quarter of the variance in actual summer precipitation in western Estonia, it has passable capacity of detecting past rainfall extremes.

Precipitation reconstruction for the southern Altay Mountains (China) from tree rings of Siberian spruce, reveals recent wetting trend

We developed six tree-ring width chronologies of Siberian spruce (Picea obovata) from the low elevation forest of the southern Altay Mountains in northern Xinjiang, China. Although the six chronologies come from different sampling sites, significant correlations existed among the chronologies (r≥0.477), and the first principal component (PC1) accounted for 72.2% of total variance over their common period 1825–2010. Correlation response analysis revealed that radial growth of Siberian spruce is mainly limited by a 12-month precipitation starting from July of the previous year to June of the current year. We therefore developed a July–June precipitation reconstruction spanning 1825–2009, which explained 65.5% of the instrumental variance for the period 1962–2009. The information of our precipitation reconstruction suggested that dry conditions existed for the periods 1829–1838, 1852–1855, 1876–1888, 1898–1911, 1919–1923, 1932–1936, 1943–1955, 1963–1968, 1973–1984 and 2007–2009, and wet conditions for the periods AD 1825–1828, 1839–1851, 1856–1875, 1889–1897, 1912–1918, 1924–1931, 1937–1942, 1956–1962, 1969–1972 and 1985–2006. Spatial climate correlation analyses with gridded land surface data revealed that our precipitation reconstruction contains a strong precipitation signal for the Altay Mountain ranges. Our reconstruction agreed with the moisture-sensitive tree ring width series of Siberian larch from the Altay Mountains of Mongolia on a decadal timescale. In addition, in contrast to a drying trend in north central China, a clear wetting trend has occurred in the southern Altay Mountains since 1980s.

Imprint of Climate Variability on Mesozoic Fossil Tree Rings: Evidences of Solar Activity Signals on Environmental Records Around 200 Million Years Ago?

Evidence of the solar activity modulation of the Earth’s climate has been observed on several parameters, from decadal to millennial time scales. Several proxies have been used to reconstruct the paleoclimate as well as the solar activity. The paleoclimate reconstructions are based on direct and/or indirect effects of global and regional climate conditions. The solar activity reconstructions are based on the production of the 14C isotope due to the interaction of cosmic ray flux and the Earth’s atmosphere. Because trees respond to climate conditions and store 14C, they have been used as proxies for both for climate and solar activity reconstructions. The imprints of solar activity cycles dating back to 10,000 years ago have been observed on tree-ring samples using 14C data, and those dating back to 20 million years ago have been analyzed using fossil tree-growth rings. All this corresponds to the Cenozoic era. However, solar activity imprints on tree rings from earlier than that era have not been investigated yet. In this work, we showed that tree rings from the Mesozoic Era (of ~200 million years ago) recorded 11- and 22-year cycles, which may be related to solar activity cycles, and that were statistically significant at the 95 % confidence level. The fossil wood was collected in the southern region of Brazil. Our analysis of the fossils' tree-ring width series power spectra showed characteristics similar to the modern araucaria tree, with a noticeable decadal periodicity. Assuming that the Earth’s climate responds to solar variability and that responses did not vary significantly over the last ~200 million years, we conclude that the solar–climate connection was likely present during the Mesozoic era.

A six hundred-year annual minimum temperature history for the central Tibetan Plateau derived from tree-ring width series

The recent unprecedented warming found in different regions has aroused much attention in the past years. How temperature has really changed on the Tibetan Plateau (TP) remains unknown since very limited high-resolution temperature series can be found over this region, where large areas of snow and ice exist. Herein, we develop two Juniperus tibetica Kom. tree-ring width chronologies from different elevations. We found that the two tree-ring series only share high-frequency variability. Correlation, response function and partial correlation analysis indicate that prior year annual (January–December) minimum temperature is most responsible for the higher belt juniper radial growth, while more or less precipitation signal is contained by the tree-ring width chronology at the lower belt and is thus excluded from further analysis. The tree growth-climate model accounted for 40 % of the total variance in actual temperature during the common period 1957–2010. The detected temperature signal is further robustly verified by other results. Consequently, a six century long annual minimum temperature history was firstly recovered for the Yushu region, central TP. Interestingly, the rapid warming trend during the past five decades is identified as a significant cold phase in the context of the past 600 years. The recovered temperature series reflects low-frequency variability consistent with other temperature reconstructions over the whole TP region. Furthermore, the present recovered temperature series is associated with the Asian monsoon strength on decadal to multidecadal scales over the past 600 years.

Annual precipitation variability inferred from tree-ring width chronologies in the Changling–Shoulu region, China, during AD 1853–2007

On the basis of a significant correlation between the tree-ring width series from Changling–Shoulu (CLSL) in north-central China and observed instrumental data, the annual total precipitation of the previous July to the current June was reconstructed since 1853 for the studied region, with the predictor variables accounting for 41.2% of the variance in the precipitation data. Distinct wet periods with precipitation levels greater than the mean (315mm) occurred in 1864–1876 and 1934–1960. Notable dry periods with precipitation less than the mean occurred in 1877–1888 and 1923–1933. The precipitation fluctuated dramatically during 1940–1970, and became relatively stable around the mean value from 1960. The CLSL precipitation series showed significant correlations with precipitation reconstructions from Mt. Xinglong, Mt. Helan, Ningwu and eastern China, suggesting that these five rainfall curves represent the general precipitation variations in the western-central environmentally sensitive zone of northern China. The calculations of the CRU grid points also indicate the existence of significant spatial correlation among these sites. Periodicity analysis showed clear 23.33-, 8.24-, 2.64- and 2.59-year cycles at a 99% confidence level for the reconstructed series during the past 155years.

Pointer years in tree-ring width and earlywood-vessel area time series of Quercus robur—Relation with climate factors near its northern distribution limit

For a long time, radial growth of pedunculate oak (Quercus robur) in relation to environmental factors has been studied in Central Europe. However, there is insufficient information on oak growth in the Baltic region. Climate–growth interactions have been mostly investigated by correlation/response analysis between ring width and climatic factors. Other wood anatomical proxies, and also pointer year analysis, which focuses on weather extremes, can be sources of additional information. Wood samples were taken from 40 sites across Latvia. Tree-ring width (TRW) and mean area of earlywood vessels (EVA) were measured. To assess differences in wood formation among sites, a PCA was performed based on pointer year series of TRW and EVA per site. The relation with climate was assessed by Pearson's correlation. Patterns of wood formation differed along west/east gradient, so that two regions (western and eastern) of Latvia were distinguished. Pointer year values were higher for TRW than for EVA and higher in the eastern than in the western region. However, the pointer year values were moderate, suggesting that there was no strict limiting factor for their formation. Pointer years of EVA were strongly related with temperature during the dormant period in both regions; June precipitation had a significant effect in the eastern region. Pointer years of TRW were correlated with spring and summer temperature in the western region and with February temperature in the eastern region; precipitation in autumn showed a negative effect. These differences can be explained by a gradient from maritime to continental climate, leading to shifts in the growth limiting factors. Extremely cold winters resulted in most of the negative pointer years of TRW and EVA.

Exploring teleconnections between the summer NAO (SNAO) and climate in East Asia over the last four centuries – A tree-ring perspective

The summer North Atlantic Oscillation (SNAO), derived from the first EOF of mean sea level pressure over the extratropical North Atlantic in July and August, has a close association with climate variability over the North Atlantic region, and beyond, on both short and long time scales. Recent findings suggested a teleconnection, through the SNAO, linking climate variability over Northern Europe with that of East Asia in the latter part of the twentieth century. Here we investigate the temporal stability of that teleconnection for the last four centuries using 4261 tree-ring width series from 106 sites and, additionally, ten climate reconstructions from East Asia. Our results showed a great potential in using tree-ring width (TRW) data to extend analyses of the SNAO influence on East Asian climate beyond the instrumental period, but preferably with a denser network. The strongest SNAO-TRW associations were found in central East Asia (in and around Mongolia) and on the eastern edge of the Tibetan Plateau. In addition, the analysis showed that the association between the SNAO and East Asian climate over the last 400 years has been variable, both among regions and at specific sites. Moreover, a clear difference in the SNAO-TRW associations was found on two examined time scales, being stronger on longer timescales. Our results indicate that TRW data can be a useful tool to explore the remote influence of the SNAO on East Asian climate in the past.

A new atmospheric circulation tree-ring index (ACTI) derived from climate proxies: Procedure, results and applications

This paper introduces a new procedure to investigate the influence of weather types on spatio-temporal tree-ring growth patterns. Within the framework of the procedure a new proxy-based climate index termed as the atmospheric circulation tree-ring index (ACTI) is calculated that combines weather-type classification data with climate proxies. The new approach is tested using a Central European multi-species tree-ring width network consisting of 115 sites. The procedure used to calculate the ACTI time series includes: 1. Monte Carlo simulations, 2. multiple testing correction, and 3. selection and grouping algorithms. The tree-ring width series are grouped according to their weather-type responses, and the ACTI time series were computed for each group.The new procedure explains the climate signal preserved in tree-ring chronologies more comprehensively because the complex interaction between the different climate elements is taken into account by using weather-type classification data. Strong correlations between the ACTI and tree-ring width series (r=0.69) and between the ACTI time series and climate gridded datasets (r>0.6) were observed. Further a correlation between ACTI and northern hemisphere mean temperatures (r=0.5) were found. These results indicate that the ACTI enables the investigation of weather-type growth relationships.

Tree ring based precipitation reconstruction in the south slope of the middle Qilian Mountains, northeastern Tibetan Plateau, over the last millennium

A tree ring (Sabina przewalskiiKom.) based millennial precipitation reconstruction on the south slope of the middle Qilian Mountains in the northeastern margin of Tibetan Plateau, China, was completed, which explains 48.5% of the variance in the instrumental precipitation from 1958 to 2004. The long‐term precipitation variation patterns were confirmed on the basis of the duration, magnitude, and intensify of the multidecadal dry (wet) events. There are several stronger multidecadal dry periods, 1092–1172, 1441–1517, and 1564–1730, whereas there is only one outstanding severe wet event of 1352–1440. The variations of the precipitation reconstruction are accordant with the glacier accumulation and dust contents of Dunde ice core and also with the variations of the precipitation, runoff, Palmer Drought Severity Index, and tree ring width series in the northeastern Tibetan Plateau. The spatial extent of the great drought in the latter half of the 15th century also concentrated on the northeastern Tibetan Plateau. The moisture variations in the northeastern Tibetan Plateau are synchronous over a large spatial and temporal range in multidecadal scale for the last millennium, especially during dry periods. Wavelet analyses and comparisons with the minimal solar activity show that the precipitation variations for the last millennium may have some association with the solar activity on multidecadal to centennial scales.

Precipitation changes in the South American Altiplano since 1300 AD reconstructed by tree-rings

Abstract. Throughout the second half of the 20th century, the Central Andes has experienced significant climatic and environmental changes characterized by a persistent warming trend, an increase in elevation of the 0 °C isotherm, and sustained glacier shrinkage. These changes have occurred in conjunction with a steadily growing demand for water resources. Given the short span of instrumental hydroclimatic records in this region, longer time span records are needed to understand the nature of climate variability and to improve the predictability of precipitation, a key factor modulating the socio-economic development in the South American Altiplano and adjacent arid lowlands. In this study we present the first quasi-millennial, tree-ring based precipitation reconstruction for the South American Altiplano. This annual (November–October) precipitation reconstruction is based on the Polylepis tarapacana tree-ring width series and represents the closest dendroclimatological record to the Equator in South America. This high-resolution reconstruction covers the past 707 yr and provides a unique record characterizing the occurrence of extreme events and consistent oscillations in precipitation. It also allows an assessment of the spatial and temporal stabilities of the teleconnections between rainfall in the Altiplano and hemispheric forcings such as El Niño-Southern Oscillation. Since the 1930s to present, a persistent negative trend in precipitation has been recorded in the reconstruction, with the three driest years since 1300 AD occurring in the last 70 yr. Throughout the 707 yr, the reconstruction contains a clear ENSO-like pattern at interannual to multidecadal time scales, which determines inter-hemispheric linkages between our reconstruction and other precipitation sensitive records modulated by ENSO in North America. Our reconstruction points out that century-scale dry periods are a recurrent feature in the Altiplano climate, and that the future potential coupling of natural and anthropogenic-induced droughts may have a severe impact on socio-economic activities in the region. Water resource managers must anticipate these changes in order to adapt to future climate change, reduce vulnerability and provide water equitably to all users.

Diameter increment of silver fir (Abies alba Mill.) in the Iłżecka Forest

A study of diameter increment of silver fir was conducted at two sites characteristic of fresh mixed broadleaved and fresh broadleaved woodland in the Ilzecka Forest in central Poland. The aim of the investigation was to follow a tree-ring width series of silver fir, with the objective of identifying the relationship between diameter increment of silver fir and climatic factors. The mean tree-ring width of 15 trees sampled in Ilzecka Forest was 2.66 mm, which is similar to the increment of fir tree rings from the Świetokrzystkie Mountains. The mean diameter increment of fir growing at the fresh broadleaved site was significantly higher than at the fresh mixed broadleaved site. Silver fir is very sensitive to harsh winters, hence after those long and severe winters in 1929, 1940, 1947, 1952 and 1956 the tree-rings were very narrow. The mean tree-ring width was higher for following periods, 1888-1962 and 1986-2005, compared with 1963-1985 when tree rings were very narrow. The process of recovery was evident from the beginning of 1980, probably due to the decrease in the SO2 emissions. During the twentieth century, warmer temperatures and nitrogen deposition have led to an increase in diameter growth of silver fir. Diameter growth of silver fir growing in the Ilzecka Forest decreased less than it did in other regions in Poland during a general fir decline between 1971 and 1980. The better growth of fir in Ilzecka Forest supports the assertation that it is well adapted to the local environmental conditions there.

Climatic response of Picea crassifolia tree-ring parameters and precipitation reconstruction in the western Qilian Mountains, China

Cores of thick leaf spruce from the western Qilian Mountains were subjected to densitometric analysis to obtain data for seven tree-ring parameters (tree-ring width, earlywood width, latewood width, maximum density, minimum density, mean earlywood density and mean latewood density). The chronologies were analyzed individually and then compared with each other. Most of these variables show moderately high values of common variance and mean interseries correlation except latewood and maximum densities. The relationships between the different tree-ring parameters and climate data are also presented. The growth/climate response analyses reveal that the radial growth of thick leaf spruce is the mainly controlled by total annual precipitation (July–June). Herein the residual ring width chronology was used to reconstruct annual (July–June) precipitation of Jiuquan for the period 1768–2009 A.D., and it accounted for 45.0% of the precipitation variance. Multi-taper spectral analysis reveals the existence of significant 11.1-year, 4.9-year, and 2.0- to 3.4-year periods of variability. Spatial analysis shows that the precipitation of Jiuquan has strong common signals for the northern margin of the Tibetan Plateau and Hexi Corridor. Drought events in our reconstruction are compared to the historical archives and other moisture-sensitive tree ring width series in the Hexi Corridor. The results reveal common climatic extremes over much of the Hexi Corridor. Many of these events have had profound impacts on the peoples of the Hexi Corridor over the past several centuries.

Environmental change without climate change?

Environmental change without climate change?

Climatic implications of a 3585-year tree-ring width chronology from the northeastern Qinghai-Tibetan Plateau

In this study we develop a tree-ring width chronology of Qilian juniper ( Sabina przewalskii Kom.) in the northeastern Qaidam Basin (northeastern Qinghai-Tibetan Plateau), China, which extends from 1580 BC to AD 2005 lasting 3585 years. This is by far the longest ring-width chronology in China. It is composed of archaeological wood samples from 13 sites, samples of living trees growing at a site with relatively good moisture condition and other long living trees from multiple sites approximately 100 m below the local upper treeline. Our results suggest that the archaeological wood and long living tree-ring width series belong to the same statistical population, which allows the construction of a single, regional composite chronology. We find that ring-width variations of the archaeological wood have statistical characteristics that are more similar to those trees from the lower part of the forest belt, where the moisture regime during the months at the onset of the growing season is the primary control on tree growth. Only after these analyses it becomes certain that the ring-width variations of the archaeological wood represent the variation of moisture conditions in the past. Therefore, the entire composite chronology is moisture-sensitive and suitable for reconstruction of the drought history and the related climate forcing over the past three millennia in the study region. The composite chronology shows considerable variations at inter-decadal to centennial timescales, with ten major multi-decadal low-growth periods corresponding to severe drought events in the past 2850 years, especially for two prominent events centered on AD 1480s and AD 1710s. On the other hand, significant high-growth periods were found centered on AD 590s and AD 1570s, and also in the past 30 years.