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Inter-annual variations of precipitation play important roles in forest management and agricultural production. This study presents a 270-year precipitation reconstruction of winter to early growing season for the central Lesser Khingan Mountains, Northeast China based on tree-ring width data of 99 tree-ring cores of Korean pine from two sampling sites near Yichun city. The reconstruction explained 46% of the variance in precipitation from the previous October to current June during the calibration period CE 1959–2017. At decadal scale, we identified four dry periods that occurred during CE 1748–1759, 1774–1786, 1881–1886 and 1918–1924, and four wet periods occurring during CE 1790–1795, 1818–1824, 1852–1859 and 2008–2017, and the period CE 2008–2017 was the wettest in the past 270 years. Power spectral analysis and wavelet analysis revealed cyclic patterns on the inter-annual (2–3 years) and inter-decadal (~11 and ~30–60 years) timescales in the reconstructed series. In addition, the Asian polar vortex has an important effect on the precipitation in our study area.

This study presents a 304-year mean July-October maximum temperature reconstruction for the southeastern Tibetan Plateau based on both tree-ring width and maximum latewood density data. The reconstruction explained 58% of the variance in July-October maximum temperature during the calibration period (1958-2005). On the decadal scale, we identified two prominent cold periods during AD 1801-1833 and 1961-2003 and two prominent warm periods during AD 1730-1800 and 1928-1960, which are consistent with other reconstructions from the nearby region. Based on the reconstructed temperature series and volcanic eruption chronology, we found that most extreme cold years were in good agreement with major volcanic eruptions, such as 1816 after the Tambora eruption in 1815. Also, clusters of volcanic eruptions probably made the 1810s the coldest decade in the past 300 years. Our results indicated that fingerprints of major volcanic eruptions can be found in the reconstructed temperature records, while the responses of regional climate to these eruption events varied in space and time in the southeastern Tibetan Plateau.

A 2665-year ring-width chronology was developed based on Qilian juniper from the upper treeline of the Animaqin Mountains on the eastern Tibetan Plateau. Correlation analysis results showed that the chronology was significantly negatively correlated with April–June maximum temperature at nearby meteorological stations, indicating that maximum temperature is the factor that limits tree growth in this area. Accordingly, we reconstructed the average April–June maximum temperature variations since 261 BC. Our regression model explained 37.9% of the total variance for the whole calibration period of 1960–2012. Our reconstruction revealed that the maximum temperature started to increase from approximately 1750 without a rapid warming trend, and the warmest period was from AD 890 to 947, as opposed to the recent period, whereas the period from AD 351–483 was the coldest. Significant periods in the wavelet power spectrum were approximately 2–8 years, 20–30 years, 30–60 years, and 60–130 years, as well as some long-term periods (more than 200 years). Comparisons with other temperature series from neighboring regions and the Northern Hemisphere as a whole support the validity of our reconstruction and suggest that it provides a representation of the temperature change for the Animaqin area, although asymmetric variation patterns in minimum and maximum temperatures were found.

Anatomical characteristics have been proven useful for extracting climatic signals. To examine the climatic signals recorded by tree-ring cell features in the Changbai Mountains, we measured cell number and cell lumen diameter, in addition to ring widths, of Korean pine (Pinus koraiensis) tree rings at sites of varied elevation, and we developed chronologies of cell number (CN), mean lumen diameter (MLD), maximum lumen diameter (MAXLD) and tree-ring width (TRW). The chronologies were correlated with climatic factors monthly mean temperature and the sum of precipitation. As shown by our analysis, the cell parameter chronologies were suitable for dendroclimatology studies. CN and TRW shared relatively similar climatic signals which differed from MLD and MAXLD, and growth-climate relationships were elevation-dependent, as shown by the following findings: (1) at each elevation, MLD and MAXLD recorded different monthly climatic signals from those recorded by TRW for the same climatic factors; and (2) MLD and MAXLD recorded climatic factors that were absent from TRW at lower and middle elevations. Cell lumen diameter proved to be an effective archive for improving the climate reconstruction for this study area.

Key message Both temperature and precipitation are strong factors of radial tree growth at all elevations in the semi-arid study area, except at the upper treeline where temperature becomes the major controlling factor.

The net primary productivity (NPP) of Pinus koraiensis , estimated from tree-ring widths, has a significant correlation with the minimum temperature in April and the summer precipitation over the past 50 years. This study investigated the relationship between climate and Pinus koraiensis net primary productivity (NPP) (estimated using tree-ring widths) and the effect of climate on NPP in the Changbai Mountains. Three typical areas of Pinus koraiensis and a broad-leaved mixed forest were investigated and sampled. NPP was estimated using biomass equations and the annual diameter at breast height, calculated from tree-ring widths. A stepwise regression was used for the quantitative analysis of the response of NPP to climate variation, whereas correlation and response analyses were used to illustrate the relationship between the climatic variables and NPP. The results showed that between 1960 and 2012, the biomass of sampled Pinus koraiensis in the Changbai Mountains almost doubled, from 107.70 to 205.29 t ha−1. The NPP of Pinus koraiensis varied steadily within a confined range over the past 52 years, with an average of 1.88 t ha−1 year−1. In this study, it was deduced that NPP was simultaneously affected by temperature and precipitation. The minimum temperature in April and the precipitation in June and July, which most affected the changes in NPP, could explain 28.4 % of the NPP variance. The extreme values of these principal climatic controls corresponded well with extreme NPP values. However, an increase in NPP caused by recent warming prior to the growing season might have been offset by a decrease in summer precipitation. Furthermore, the effect of temperature change on NPP was complex. An increase in monthly low temperatures induced by warming acted to increase NPP, while the monthly high temperatures during the growing season had a negative impact on NPP for the drought.

The importance of a better understanding of the growth response of forest to climate change for managing and conserving forest has been realized. In this study, we developed the ring-width chronologies of Korean pine (Pinus koraiensis), one of the main constructive species of Changbai Mountain in northeastern China, to examine the radial growth-climate relationships. The stability of these relationships before and after abrupt climate change was evaluated. We built regression equations to project the future growth of the species under future climate change scenarios projected by the Providing Regional Climates for Impacts Studies (PRECISs) climate model. The results were as follows: (1) The chronologies in the three elevation gradients, HY1 at 740. m.s.l., FA at 940. m.s.l. and HY2 at 1258. m.s.l., had the good spatial similarity with high Gleichlafigkeit (GLK) indices; however, significant differences still existed between the growth-climate relationships of the three sites. The width chronology of Korean pine at site HY1 was positively correlated with the precipitation in September of the previous year (p

As a transitional zone between westerlies and the Asian Monsoon system, the northeastern part of the Tibetan Plateau (NETP) is highly sensitive to climate change. The record of historical regional moisture variation in the NETP is essential for understanding climatic variation and its relationship with different climate systems in this area. Using principal component analysis, a time series was extracted from sixteen moisture-sensitive tree-ring series to investigate the regional moisture variation in the NETP over the past 150 years. We find that the first principal component (PC1) represents 46.9 % of the total variance, reflecting a common growth response to the climate factor. A spatial correlation analysis of PC1 with the gridded meteorological data demonstrated that the precipitation in May–June was the major factor in controlling tree-ring growth. Further analysis indicated that the westerlies had a sustained influence on rainfall in the NETP over the past 150 years. In addition, the rainfall in the NETP may be closely associated with the East Asian Monsoon (EAM). Severe drought years commonly correspond to years of a negative phase of the North Atlantic Oscillation and stronger EAM years over the past 150 years.

Euphrates poplar (Populus euphratica) is a key species of Tugai forests in the central Asian deserts and has been the topic of dendrochronological studies in west China since the 1980s. However, little is known about its growth performance at its highest occurrence in the southern Qaidam Basin of the northern Tibetan Plateau. Increment cores of the Euphrates poplar population there did well cross-date and thus showed a high dendrochronological potential. Its growth was persistently positively correlated with temperature from previous September to current August although not significant throughout. The annual precipitation of around 41 mm can not exert any significant effect on Euphrates poplar growth in view of the extremely high annual pan evaporation of 2,150 mm. Water in the nearby Tuolahai River is limited to the period from June–September. The positive correlation of tree growth with spring/early summer temperature indicates that the riparian Euphrates poplar trees may benefit from an increasing river runoff due to an advanced and accelerated snow and glacier melting under warmer conditions. An above-average autumn/early winter temperature in the preceding year may lead to an extended water flow in the river bed and hence to an increased tree growth in the next year. It is crucial to protect this invaluable natural forest from undue human activity.

Tree-ring width standard chronologies were created from juniperus przewalskii Kom data collected in the Lancang River Headwaters region. Statistical analysis results showed high correlation (r = 0.69) between the composite tree-ring chronology and instrumental streamflow records at the Xiangda Hydrological Station during the annual September–August interval. Streamflow of the Zaqu River in the Lancang river source region was reconstructed for the past 419 years. The model was stable and revealed 14 extremely dry years and 6 extremely wet years. The results showed relatively low streamflow periods occurred during 602–1614, 1633–1656, 1684–1697, 1712–1722, 1735–1753, 1817–1829, 1847–1861, 1874–1884, 1946–1959, 1961–1977, and 1990–2000. Relatively high streamflow periods occurred during 1615–1630, 1657–1678, 1698–1711, 1754–1783, 1803–1813, 1830–1840, 1862–1873, 1892–1909, and 1932–1945. Comparison with tree-ring based streamflow reconstructions and chronologies from surrounding areas provided a high degree of confidence in our reconstruction. The empirical mode decomposition analysis suggests the existence of significant periods with intervals of 2–4, 5–9, 11–16, and 26–50 years. Regional comparison indicated that our reconstruction was associated with large-scale atmospheric-oceanic variability, such as the El Nino–Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO) index, Pacific Decadal Oscillation (PDO) index, and East Asian monsoon variation. This research provides a useful foundation for water resource planning and management guidance in the Three-River Headwaters Region.

A tree-ring width chronology was developed using the tree-ring cores of Huangshan pine (Pinus taiwanensis Hayata) from the Dabie Mountains, central China. Descriptive statistics of the chronology indicated that Huangshan pine showed a common signal likely associated to climate. A correlation analysis was conducted between the chronology and climate variables, and the results demonstrated that the radial growth was positively correlated to the February–July mean temperature. The February–July mean temperature was reconstructed from AD 1869 to 2008 for the Dabie Mountains. The reconstruction can explain 49.8 % of the variance for the calibration period (1959–2008). On the decadal timescale, for the reconstructed temperature during the reliable period 1889–2008, above-mean temperature periods occurred in AD 1889–1898, 1903–1908, 1922–1933, 1945–1950, 1955–1958, and 1994–2008, whereas below-mean temperature periods occurred in AD 1899–1902, 1909–1921, 1934–1944, 1951–1954, and 1961–1993. The reconstruction indicates that the early years of the twenty-first century represent the warmest period and that the period of 1910–1919 is the coldest decade over the last 120 years. The reconstructed temperature corresponds well with the observed temperature in Wuhan, Hubei Province, suggesting that the reconstruction can represent the local climatic signals and may also reflect the regional climatic signals.

Knowledge of the spatial pattern and temporal relationships between tree-growth and climatic factors are important not only for the projection of forest growth under varying climate but for dendroclimatology in general. Here, we systematically investigated tree-growth climate relationships of Picea crassifolia at upper treeline in the Qilian Mts., northwestern China. 297 trees from eleven sites, covering a large part of the natural range of this species, show increasing and partly divergent correlations with temperature in the most recent decades. The dominant signal at all sites was a strengthening of negative correlations of annual radial growth with summer temperature. In a subset of trees at six sites, a strengthening positive correlation with summer temperatures existed as well. Wetter and high altitude sites tended to show a higher percentage of trees that are positively correlated with warming temperatures, indicating that some individuals there may take advantage of warmer conditions. Divergent responses between the two subpopulations clustered by their response to climate factor were significantly stronger in the last 30 years compared to earlier time slices. In the same time frame, hydrothermal conditions of the investigation area changed to a drier and warmer combination. Drought conditions, most likely affecting the radial growth of most P. crassifolia, have been intensifying over time and expanding spatially from the middle Qilian Mts. to most of our study area during the last half century. While explanations such as methodological effects due to trend removal or human disturbance at the sampling sites might be able to explain the result at single sites, the spatial and temporal co-occurrence of large scale changes in climate and tree growth suggests a causal link between them.

A network of nine Smith fir (Abies georgei var. smithii) ring-width chronologies was constructed from sites ranging in elevation from 3,550 to 4,390 m above sea level (a.s.l.) in the Sygera Mountains, southeastern Tibetan Plateau. High-elevation trees had lower growth rates than did low-elevation trees. The mean tree-ring series intercorrelation (RBAR) increased with elevation. Principal component analysis identified three elevation zones (around 3,600, 3,800, and >4,200 m a.s.l.) with distinctive tree-ring growth patterns. Five chronologies with elevation >4,200 m a.s.l. were highly correlated. Overall, the initiation of tree-ring growth in Smith fir is controlled by common climatic signals, such as July minimum temperature, across a broad altitudinal range. Precipitation was not a growth-limiting factor across stands. Regardless of differences in stand elevation, topographical aspect, and tree age, the radial growth of Smith fir trees was markedly similar in response to common climatic signals, perhaps as a result of the relatively high-elevation of these forests (above 3,550 m a.s.l.) and the abundant summer monsoon rainfall. In addition, radial tree growth along the altitudinal gradients was indicative of a recent warming trend on the southeastern Tibetan Plateau.

The seasonal dynamics of cambial activity of Chinese pine (Pinus tabulaeformis Carr.) was studied at the northern limit of its natural distribution in a semi-arid grassland ecosystem in North China. We collected micro-cores from five even-aged trees at weekly intervals from April 15 to September 16, 2006. Cell division in the cambial zone of these trees started within the third week of May. In June and July the rate of xylem cell production was highest and around mid-August cell division ended. However, cell-wall formation was not yet completed around mid-September. The cell-division period appears to coincide with the time of highest monsoon precipitation and of above 0 °C daily minimum temperature. Moreover, the cambium activity period seems to be in agreement with the time of the highest number of sunshine hours/day. These preliminary results are important for dendroclimatic studies with Chinese pine in North China and can furthermore be used as a benchmark for future monitoring activities in ecologically similar areas.

Taking Chinese pine in Qianshan Mountains as a sample, the tree ring width chronology including Standard, Residual, and Arstan chronologies was established. The results show that the tree ring width of Chinese pine is highly correlated with the temperatures from May to July and from September to November. Statistically significant positive correlations were observed between tree ring width and the extreme minimum temperatures in July and mean minimum temperatures in September. The chronology was significantly or very significantly correlated with extreme minimum temperatures in December and the following January, with mean minimum temperatures in January, with annual precipitation and with precipitation in April, May and the following December. The Chinese pine responded strongly to the monthly/yearly water vapor pressure and relative humidity. Annual and largely monthly evaporation in April–July had a negative effect on tree growth, and was particularly striking for evaporation in April–July. The narrow tree rings recorded by the chronology demonstrated the 30 occasions of extreme drought since 1800. The growth of Chinese pine in the Qianshan mountains were also affected by climate changes on a hemispheric and global scale. There were 11-, 23-and 50-year-common periodicities between the chronology and solar activity and 10-, 20-and 45-year-common periodicities between the chronology and geomagnetic activity.

Long tree-ring chronologies provide a unique calendar record that is of value for archaeological dating. This paper reports the results of the dendrochronological study of Przewalsk juniper (Sabina przewalskii Kom) excavated from Xiatatu tombs of the Tubo Kingdom in Guolimu County, Delingha City, Qinghai Province, China. A 2332-year tree-ring chronology was constructed from archaeological wood, and calendar years were assigned to date the tombs. For two of the tombs, the dating results are in accordance with the presumed dates as resulting from the tomb shapes and the excavated objects, especially the coffin panel paintings and historical documents. The date of the Tubo tombs provides a calendar scale for studying the cultural history of the Tuyuhun during the Sui dynasty and the southern and northern dynasties, and the cultural exchanges between China and foreign countries based on the pictures.

Qilian juniper (Sabina przewalskii Kom.) and Qinghai spruce (Picea crassifolia Kom.) represent different tree functional types, which can be found extensively in northwestern China. The former is drought-tolerant, whereas the latter is hygrophilous and shade-tolerant. We compared their intrinsic water-use efficiency (iWUE, inferred from carbon isotopic discrimination, δ13C, in their wood) as a function of atmospheric CO2 concentration, [CO2], and climate. δ13C of spruce was consistently about \({1.23\permille}\) higher than that of juniper in semi-arid areas but was lower in arid areas. This difference was stable over time and demonstrated strong cross-correlations between species, although some subtle high-frequency (2 or 3 years) variations existed in both species, suggesting that regional climate may control carbon isotope discrimination. The \({{C_{\rm i}/C_{\rm a}}}\) ratio (the [CO2] values in leaf intercellular and the atmosphere, respectively) of the juniper increased steadily over time, whereas that of the spruce showed a long-term downward trend. IWUE increased at all sites over the 150-year study period, mainly caused by increasing [CO2]. The relationship between iWUE and [CO2] reveals that the spruce was more sensitive than the juniper to increasing [CO2], suggesting a species-specific adaptation to long-term environmental changes. Correlations between the high-frequency variations in stable carbon discrimination (Δ) and climate indicate similar intra-site responses to climate in both species, but different response strengths. Overall, complex interactions of temperature and moisture on stable carbon discrimination during current growth seasons of both species were environmental-determined. Regulation of gas exchange and reduced transpiration may influence water and energy budgets directly; therefore species-dependent responses of trees to elevated CO2 should be considered in future research on global plant physiological ecology.

A tree ring width chronology developed from 58 samples taken from Chinese pine trees (Pinus tabulaeformis Carr.) growing in Shenyang city was studied to analyze the effects of solar activity, Global Surface Air Temperature Anomalies (GSATA) and the Pacific Decadal Oscillation (PDO) on annual radial growth. An excellent response of tree rings to solar activity and global environmental change was revealed, indicating that these urban Chinese pine trees are a suitable proxy for Sun-Earth system research despite their location in Shenyang, an industrial city. The information derived from annual growth rings of urban Chinese pine trees coincides with records from undisturbed trees in a natural location, and demonstrates significant synchronous response to solar activity in the periodic bands of 5–8, 10–12 and 20–30 years. The wave signal of tree growth was also affected and amplified by the combined effect of the PDO from 1900 to 2004 and GSATA from 1880 to 2004 with a short lag time, revealing 5–8, 11–13, and 20–23 year oscillatory modes. At 20–30 year timescale, Chinese pines validated the strong GSATA influence signal at 20.8 years, and may be the primary cause of the 20 and 23 year periodic waves of tree rings. Shenyang urban tree ring growth also showed high frequency variation (2—4 y) that may be due to low periodicity of solar activity, GSATA, PDO and local climate variations, especially in the 2–4 years band width.

February-May temperature strongly affects ecological processes and socio-economics in central China, yet its long-term variability has not been thoroughly assessed due to the shortness of instrumental records. In order to improve the understanding of the regularities of temperature variability in central China, in this study, we present a new tree-ring chronology from the Shengnongjia Mountains in central China which provides a valuable 245-year record of temperature variability. The reconstructed temperature correlated strongly with February-May mean temperature records of the Fangxian meteorological station from AD 1958 to AD 2011, and the derived reconstruction explained 44.5 % of the instrumental temperature variation during this period. The study shows that this region experienced three warm periods and two cool periods, i.e., the major warm periods occurred in AD 1783-1806, AD 1879-1909, and AD 1975 to the present, whereas the cool intervals occurred in AD 1807-1878 and AD 1910-1974. This reconstruction could aid in the evaluation of regional climate variability in subtropical China.

Using a network of tree-ring data, we show that there had been significant growth decline in the 1920s and early 1930s throughout a wide area of northern China. This growth depression is indicative of a severe and sustained drought in the 1920s and early 1930s, which was then confirmed with a variety of historical and instrumental records including hydrological, meteorological, and documentary evidence. The 1920s drought had a devastating effect not only on agricultural productivity, hydrological resources and society in the affected areas, but also on natural vegetation, as inferred from the tree-ring network and historical records. This research offers a picture of the drought calamity during the 1920s and early 1930s in northern China, and demonstrates the potential to identify spatial anomalies of large-scale drought using tree-ring networks in the semi-arid and arid areas of northern China.

This study explores the relationships between the Normalized Difference Vegetation Index (NDVI), recorded above-ground grass biomass and tree-ring width index of relict Meyer spruce (Picea meyeri Rehd. et Wils.) forest in the typical steppe, north China. The average NDVI in May, June and August derived from an area of 0.5 degrees x 0.5 degrees shows a large correlation with measured above-ground production, indicating that NDVI can reflect the approximate variability of above-ground biomass in the typical steppe. The integrated NDVI from 20 May to 10 July also exhibits high agreement with tree-ring width series of Meyer spruce from 1982 to 1994, which is attributed to their common response to precipitation in the previous August-October and current May. This study provides a basis for linking remotely sensed NDVI of grassland to tree growth in semi-arid grassland.

Meyer spruce (Picea meyeri Rehd. et Wils.) is a relict conifer, and Chinese leymus (Leymus chinensis [Trin.] Tzvel.) is a dominant grass in typical steppe of the Xilin River Basin, northern China. Herein, we evaluated the relationships between tree-ring width index of Meyer spruce, climate and above-ground biomass of Chinese leymus, and reconstructed above-ground biomass of Chinese leymus from 1955 to 1994 using tree rings. Both Meyer spruce and Chinese leymus exhibited significant positive (P < 0.05) growth response to May precipitation during the current growing season. In addition, the growth of Chinese leymus was significantly correlated (P < 0.05) with the sum of current July and August precipitation. Two predominant linear relationships between ring width and annual grass production were found, and each corresponding to different precipitation patterns in this region. With reference to seasonal precipitation patterns, the above-ground biomass of Chinese leymus from 1955 to 1994 was reconstructed using two models derived from tree-grass growth relationships. The comparison of climate-growth relationships between relict Meyer spruce and dominant Chinese leymus pointed to the different adaptation strategies of two ecosystem elements to the semi-arid steppe climates. The reconstruction of grass production could reduce the gap in our knowledge of the past dynamics of typical steppe, allowing verification of model estimates of natural climate fluctuations. This may be also an important step towards understanding the response of different ecosystem components to future climate change in the typical steppe, and delivering the baseline reference for a sound steppe management plan.

The interest in national terrestrial ecosystem carbon budgets has been increasing because the Kyoto Protocol has included some terrestrial carbon sinks in a legally binding framework for controlling greenhouse gases emissions. Accurate quantification of the terrestrial carbon sink must account the interannual variations associated with climate variability and change. This study used a process-based biogeochemical model and a remote sensing-based production efficiency model to estimate the variations in net primary production (NPP), soil heterotrophic respiration (HR), and net ecosystem production (NEP) caused by climate variability and atmospheric CO2 increases in China during the period 1981-2000. The results show that China's terrestrial NPP varied between 2.86 and 3.37 Gt C yr(-1) with a growth rate of 0.32% year(-1) and HR varied between 2.89 and 3.21 Gt C yr(-1) with a growth rate of 0.40% year(-1) in the period 1981-1998. Whereas the increases in HR were related mainly to warming, the increases in NPP were attributed to increases in precipitation and atmospheric CO2 . Net ecosystem production (NEP) varied between -0.32 and 0.25 Gt C yr(-1) with a mean value of 0.07 Gt C yr(-1), leading to carbon accumulation of 0.79 Gt in vegetation and 0.43 Gt in soils during the period. To the interannual variations in NEP changes in NPP contributed more than HR in arid northern China but less in moist southern China. NEP had no a statistically significant trend, but the mean annual NEP for the 1990s was lower than for the 1980s as the increases in NEP in southern China were offset by the decreases in northern China. These estimates indicate that China's terrestrial ecosystems were taking up carbon but the capacity was undermined by the ongoing climate change. The estimated NEP related to climate variation and atmospheric CO2 increases may account for from 40 to 80% to the total terrestrial carbon sink in China.

Dendroclimatic techniques were used to assess the climate–growth relationships of refugial Meyer spruce (Picea meyeri Rehd. et Wils.) on a sandy substrate in semi-arid grassland of north China. Statistical analysis of the tree-ring data showed a mean series intercorrelation of 0.47, a signal-to-noise ratio of 14.44, and a mean sensitivity of 0.18, indicating suitability for climatic analysis. Radial growth was positively correlated with precipitation in February and May of the current year, and in September of the preceding year. However, radial growth of Meyer spruce also correlated negatively with mean monthly temperature in current May, of which mean maximum temperature explained most of the observed variation. In addition, radial growth negatively correlated with solar radiation over most of the year. Rainfall appeared to be the dominant growth-limiting factor in this semi-arid grassland, with temperature and solar radiation being of lesser importance. This study suggests that Meyer spruce in this stand is promising for dendroclimatic and ecological studies because of good cross-dating characteristics and high sensitivity to climate.

[1] Improved understanding of climate influences on tree ring stable carbon isotope (δ13C) ratios for Qilian juniper (Sabina przewalskii Kom.) will improve prospects for long climate reconstructions in northwestern China's Qaidam Basin, where weather stations are widely scattered with relatively short records. Here, we developed an annual-resolution δ13C series from 1800 to 2005 for trees in this extremely arid, high-elevation area. As expected, a significant decline in δ13C (of about 3.5‰) occurred from 1850 to 2005 in response to increasing atmospheric CO2 concentrations and decreasing atmospheric δ13C. High-frequency correlation analysis based on comparison of the tree ring δ13C chronology with recorded weather parameters revealed that mean temperature during the current growing season (April–August) most strongly influenced tree ring δ13C discrimination from 1956 to 2005. To clarify the climatic implications of the long-term trend, we systematically compared four previously published approaches to remove the effects of decreasing atmospheric δ13C from the climate signals. The optimal correction, which accounted for the decline in atmospheric δ13C (δ13Ccor) and for a discrimination rate of about 0.016‰ ppmv−1 for the CO2 partial pressure, captured the strongest temperature signal (r = 0.75, P < 0.001). The historical mean April–August temperatures inferred from the correlations of tree ring δ13C with climate data revealed a persistent warming trend during the past two centuries, especially since the 1980s. Our results therefore reveal a high potential for reconstruction of growing season temperatures on a millennial scale in the northeastern Tibetan Plateau.

The stable carbon isotope composition (delta(13)C) of tree rings in a climate-sensitive region can provide a retrospective view of changes in environment and climate. Here, we report on the development of the first annually resolved delta(13)C tree ring chronology obtained from natural forests on the northeastern Tibetan Plateau. Climate data show a warming trend and more frequent droughts occurring in the research region since the 1970s. The isotope record of Qinghai spruce (Picea crassifolia) spans the period 1890-2002 with a general decreasing trend over the last century followed by an abrupt increase in delta(13)C over the last decade. The stable carbon discrimination against heavier atmospheric carbon (Delta(13)C) is negatively correlated to May temperature and positively correlated with June-July precipitation. The regional Palmer drought severity index (PDSI) correlated significantly with Delta(13)C series after 1960, whereas this relationship was not stable over the period 1933-1960. However, much stronger correlations were observed between the high-frequency anomalies in annual Delta(13)C and PDSI in June and July during the period 1933-2002. The temporal stability analysis revealed trends in the response to drought stress affecting tree's Delta(13)C linked to climatic warming. Intrinsic water-use efficiency increased by 7.7% in Qinghai spruce in response to increased severity of regional drought during the 1990s compared to the average of the previous decade. Our preliminary results suggest that carbon isotope in certain tree taxa growing on Tibetan Plateau may be an effective proxy for reconstructing regional drought.

Warming-induced drought has widely affected forest dynamics in most places of the northern hemisphere. In this study, we assessed how climate warming has affected Picea crassifolia (Qinghai spruce) forests using tree growth-climate relationships and the normalized difference vegetation index (NDVI) along the Qilian Mountains, northeastern Tibet Plateau (the main range of Picea crassifolia). Based on the analysis on trees radial growth data from the upper tree line and the regional NDVI data, we identified a pervasive growth decline in recent decades, most likely caused by warming-induced droughts. The drought stress on Picea crassifolia radial growth were expanding from northeast to southwest and the favorable moisture conditions for tree growth were retreating along the identical direction in the study area over the last half century. Compared to the historical drought stress on tree radial growth in the 1920s, recent warming-induced droughts display a longer-lasting stress with a broader spatial distribution on regional forest growth. If the recent warming continues without the effective moisture increasing, then a notable challenge is developed for Picea crassifolia in the Qilian Mountains. Elaborate forest management is necessary to counteract the future risk of climate change effects in this region.

[1] Daily and monthly maximum and minimum surface air temperatures at 66 weather stations over the eastern and central Tibetan Plateau with elevations above 2000 m were analyzed for temporal trends and spatial variation patterns during the period 1961 - 2003. Statistically significant warming trends were identified in various measures of the temperature regime, such as temperatures of extreme events and diurnal temperature range. The warming trends in winter nighttime temperatures were among the highest when compared with other regions. We also confirmed the asymmetric pattern of greater warming trends in minimum or nighttime temperatures as compared to the daytime temperatures. The warming in regional climate caused the number of frost days to decrease significantly and the number of warm days to increase. The length of the growing season increased by approximately 17 days during the 43-year study period. Most of the record-setting months for cold events were found in the earlier part of the study period, while that of the warm events occurred mostly in the later half, especially since the 1990s. The changes in the temperature regime in this region may have brought regional-specific impacts on the ecosystems. It was found that grain production in Qinghai Province, located in the area of prominent warming trends, exhibited strong correlations with the temperatures, although such relationships were obscured by the influence of precipitation in this arid/semiarid environment in juniper tree ring records. In western Sichuan Province under a more humid environment, the tree growth ( spruces) was more closely related to the changing temperatures.

Understanding the vertical distributions of soil organic carbon (SOC) is key to predicting and simulating the influences of climate, global change, and human activities on the terrestrial carbon cycle. SOC was measured at soil depths of 0–10, 0–20, 0–30, 0–50, and 0–100 cm in 2473 soil profiles during China’s second national soil survey that was conducted from 1979 to 1992. SOC was spatially extrapolated for China. Mean SOC densities in the top 1 m ranged from 4.65 kg/m2 for bare ground to 17.32 kg/m2 in grassland land cover. SOC in the top 1 m of soil was estimated at 82.5 ± 19.5 Pg C. The total SOC pool held in the top 10, 20, 30, 50, and 100 cm are 22%, 41%, 54%, 74%, and 100%, respectively. One of the objectives of the study is to examine the association of SOC content with climate and to estimate SOC storage in land-cover types at different soil depths. A partial correlation analysis shows that the mean annual precipitation was positively correlated with SOC content and the mean annual temperature was negatively correlated with SOC content, across all depths. The vertical distribution of SOC had a slightly stronger association with temperature than with precipitation in China.

International audience; Using tree-ring analysis coupled with historical records, we investigated the possibility of developing a tree-ring network in North China, and the possible disturbance for the dieback of Meyer spruce (Picea meyeri) forest in typical steppe. Four tree-ring chronologies were employed: one for Meyer spruce and Korean spruce (Picea koraiensis) in eastern Inner Mongolia, and two for Chinese pine (Pinus tabulaeformis) in central Inner Mongolia. Significant parallel behaviour between the chronologies revealed the possibility of developing a large-scale tree-ring network in North China. In addition, the coincident growth decline in the 1920s in Chinese pine and Korean spruce chronologies revealed the most severe drought period for more than 200 years in North China, which was confirmed by converging lines of historical events. A clear correspondence between a peak in the age distribution (1933-1935) and a persistent drought event from 1922 to 1932 implied that the extreme drought in the 1920s was probably the underlying cause of Meyer spruce mortality.; La sécheresse extrême des années 1920 et son effet sur la croissance des arbres : une étude dendrochronologique en Chine du Nord. La dendrochronologie et l'analyse de documents historiques ont été utilisées d'une part pour évaluer le potentiel d'une base de données dendrochronologiques régionale et d'autre part pour vérifier l'existence d'une perturbation responsable du déclin des forêts d'épicéa de Meyer (Picea meyeri) dans la steppe typique. Quatre séries dendrochronologiques ont été construites : une pour l'épicéa de Meyer et l'épicéa de Corée (Picea koraiensis) dans l'Est de la Mongolie intérieure et deux pour le Pin chinois (Pinus tabulaeformis) en Mongolie intérieure centrale. Les tendances observées dans ces quatre séries dendrochronologiques sont significativement comparables. Ainsi, ces quatre séries suggèrent un fort potentiel pour une base de données dendrochronologiques applicable aux échelles locale et régionale en Chine du Nord. De plus, le Pin chinois et l'épicéa de Corée ont tous deux montré un déclin de leur croissance dans les années 1920, ce qui indique une période de sécheresse sévère et soutenue inégalée depuis 200 ans en Chine du Nord. Ceci est confirmé par des événements historiques synchrones. Une nette correspondance entre un pic dans la distribution des âges (1933-1935) et une sécheresse soutenue de 1922 à 1935 impliquent que la sécheresse des années 1920 était probablement une des causes de la mortalité de l'épicéa de Meyer, espèce particulièrement sensible à la sécheresse.

The Oytag valley, about 100 km west of Kashi (Kashgar), is one of the few valleys with forests in the Kunlun Mountains. It underwent severe forest destruction in the late 1950s, and about only one fourth of the natural forest remains. Since the early 1980s, forest conservation and artificial regeneration have been carried out in the valley.

Sabina przewalskii is the longest living endemic tree species in the northeastern Tibetan Plateau, and has been widely employed in tree ring based climate research in China. However, most dendroclimatic reconstructions have been primarily based on empirical relationships between tree growth and climate factors identified by statistical assessment. To date, the physiological relationships between tree growth and their limiting climate factors have not been properly assessed. Here, we simulated the physiological response of Sabina przewalskii tree growth to major limiting climate factors based on the Vaganov-Shashkin (VS) model. The VS modeled results validated the relationships between tree ring and climate factors constructed by statistical models, both approaches suggesting that precipitation during the early growing season, especially in May and June, has significant effect on tree growth, while temperature mainly affects tree growth by warming-induced drought and by extending the growing season. Under current and projected climate scenarios, our modeling results predict an increase in radial growth of Sabina przewalskii around the Qaidam Basin, with the potential outcome that regional forests will increase their capacity to sequester carbon.