Sabina Przewalskii Kom Research Articles

Study on Biomass Models of Artificial Young Forest in the Northwestern Alpine Region of China

The artificial young forest is an important component of ecosystems, and biomass models are important for estimating the carbon storage of ecosystems. However, research on biomass models of the young forest is lacking. In this study, biomass data of 96 saplings of three tree species from the southern foot of the Qilian Mountains were collected. These data, coupled with allometric growth equations and the nonlinear joint estimation method, were used to establish independent, component-additive, and total-control compatible models to estimate the biomass of artificial young wood of Picea crassifolia (Picea crassifolia Kom.), Sabina przewalskii (Sabina przewalskii Kom.), and Pinus tabulaeformis (Pinus tabuliformis Carr.). The distribution characteristics of the biomass components (branch, leaf, trunk, and root biomass) and the goodness of fit of the models were also analyzed. The results showed that (1) the multiple regression models with two independent variables (MRWTIV) were superior to the univariate models for all three tree species. Base diameter was the best-fitting variable of the univariate model for Picea crassifolia and Pinus tabulaeformis, and the addition of base diameter and crown diameter as variables to the MRWTIV can significantly improve model accuracy. Tree height was the best-fitting variable of the univariate model of Sabina przewalskii, and the addition of tree height and crown diameter to the MRWTIV can significantly improve model accuracy; (2) the two independent variable component-additive compatible model was the best-fitting biomass model. The compatible models constructed by the nonlinear joint estimation method were less accurate than the independent models. However, they maintained good compatibility among the biomass components and enabled more robust estimates of regional biomass; and (3) for the young wood of Picea crassifolia, Sabina przewalskii, and Pinus tabulaeformis, the aboveground biomass ratio of each component to total biomass was highest for leaf biomass (26%–68%), followed by branch (10%–46%) and trunk (11%–55%) biomass, and the aboveground biomass was higher than the underground biomass. In conclusion, the optimal biomass model of artificial young forest at the sampling site is a multivariate component-additive compatible biomass model. It can well estimate the biomass of young forest and provide a basis for future research.

The Influence of Climate Change on Three Dominant Alpine Species under Different Scenarios on the Qinghai–Tibetan Plateau

The Qinghai–Tibetan Plateau (QTP) with high altitude and low temperature is one of the most sensitive areas to climate change and has recently experienced continuous warming. The species distribution on the QTP has undergone significant changes especially an upward shift with global warming in the past decades. In this study, two dominant trees (Picea crassifolia Kom and Sabina przewalskii Kom) and one dominant shrub (Potentilla parvifolia Fisch) were selected and their potential distributions using the MaxEnt model during three periods (current, the 2050s and the 2070s) were predicted. The predictions were based on four shared socio-economic pathway (SSPs) scenarios, namely, SSP2.6, SSP4.5, SSP7.0, SSP8.5. The predicted current potential distribution of three species was basically located in the northeastern of QTP, and the distribution of three species was most impacted by aspect, elevation, temperature seasonality, annual precipitation, precipitation of driest month, Subsoil CEC (clay), Subsoil bulk density and Subsoil CEC (soil). There were significant differences in the potential distribution of three species under four climate scenarios in the 2050s and 2070s including expanding, shifting, and shrinking. The total suitable habitat for Picea crassifolia shrank under SSP2.6, SSP4.5, SSP7.0 and enlarged under SSP8.5 in the 2070s. On the contrary, the total suitable habitat for Sabina przewalskii enlarged under SSP2.6, SSP4.5, SSP7.0 and shrank under SSP8.5 in the 2070s. The total suitable habitat for Potentilla parvifolia continued to increase with SSP2.6 to SSP8.5 in the 2070s. The average elevation in potentially suitable habitat for Potentilla parvifolia all increased except under SSP8.5 in the 2050s. Our study provides an important reference for the conservation of Picea crassifolia, Sabina przewalskii, Potentilla parvifolia and other dominant plant species on the QTP under future climate change.

A 2917-year tree-ring-based reconstruction of precipitation for the Buerhanbuda Mts., Southeastern Qaidam Basin, China

In this study, we developed the tree-ring width chronology for the period of 1404 BCE to 2015 CE using Qilian juniper (Sabina przewalskii Kom.) trees collected from the Buerhanbuda Mts. in the southeastern Qaidam Basin (QB) near Nuomuhong Village, Qinghai Province. This is the first and longest chronology to date in this region. Based on the relationships between the tree-ring width chronology and climate data, the annual precipitation from previous July to current June (July-June) was reconstructed for the past 2917 years from 902 BCE to 2015 CE. This reconstruction accounted for 47.9% of the total variance in the actual July-June precipitation in the calibration period (1957–2015). The full reconstruction captured distinct wet and dry variability, and contained evidence of some low-frequency climate signals. We identified 13 wet and 12 dry periods, of which 1443–1503 CE and 1789–1836 CE were the two longest dry periods. General agreements in the low-frequency variations between the July-June precipitation and other moisture-sensitive records for the northeastern Tibetan Plateau (TP) suggested that the reconstruction in this study represented a regional signal. Spatial correlations with gridded precipitation data also indicated that the reconstructed July-June precipitation could adequately represent climate fluctuations over a large area of the northeastern TP. The new tree-ring width chronology and precipitation reconstruction are important for understanding natural climate change in the southeastern QB.

Centennial-scale process activity in a complex landslide body in the Qilian Mountains, northeast Tibetan Plateau, China

Mass movements in China typically encompass landslides, rockfalls, and debris flows, and these processes affect almost 70% of all mountain areas of China. An improved understanding of geomorphic process dynamics and their drivers and process histories are important prerequisites for a proper assessment and a sustainable management of mountain hazards. Tree rings have on varied occasions proven to be a reliable tool for the acquisition of data on past mountain hazards. Here we present the first reconstruction of past landslide activity on a slope in the Qilian Mountains, northeast Tibetan Plateau, China. To this end, a total of 543 Qilian juniper (Sabina przewalskii Kom.) samples were selected from 239 trees growing on or next to a complex landslide body, with the aim to reconstruct past landslide histories at the site. The dataset of disturbed trees was complemented with 174 increment cores from 84 reference Qilian juniper trees growing on three adjacent, yet undisturbed sites. Based on the dating of the samples and the interpretation of growth disturbances (GD) in the tree-ring series of affected trees, we provide the first reconstruction of past landslides as retrieved from a dendrogeomorphic record covering more than a millennium (956–2011 CE). Results show that the first detectable GD occurred as early as in 1042 CE, followed by seven major landslide reccurrences in 1703, 1816, 1848, 1863, 1913, 1970, and 1982. Comparison between our landslide record and a dendroclimatic precipitation reconstruction points to the crucial role of major, longer-term wet precipitation anomalies on landslide occurrence.

Separating temperature from precipitation signals encoded in tree-ring widths over the past millennium on the northeastern Tibetan Plateau, China

Tree-ring width chronologies from the upper timberline are an important material to reconstruct past temperature variability on the northeastern Tibetan Plateau (NTP). However, precipitation signals are often encoded in the upper timberline chronologies, which complicate the temperature reconstructions and should be removed properly. Here, we propose to use the chronologies from the middle to lower forest zones to remove the precipitation signals encoded in the upper timberline chronologies on the NTP, as tree growth at the two elevation zones records similar precipitation signals but has different temperature responses. We compiled a dataset of 13 Qilian juniper (Sabina przewalskii Kom.) tree-ring width chronologies, and employed two independent methods to develop millennial (AD 1000–2000) temperature reconstructions on the NTP. The two reconstructions are very consistent with each other over the past millennium, with a correlation of 0.97, and account for more than 50% of the observed temperature variance during 1958–2000. Both reconstructions contain little precipitation signals, suggesting that we have extracted purer temperature information than before. Our reconstructions show similar warm-cold patterns to the temperature records from the surrounding areas, indicating that they are capable of representing large-scale temperature variability during the past millennium. Comparison of our reconstructions with five millennial Northern Hemisphere (NH) temperature series indicates that temperature changes on the NTP are generally distinct from the NH temperature patterns except for the long-term trend during the past millennium, suggesting specific characteristics of regional temperature variability. The distinct variations may be related to the influence of local precipitation, which generally has inverse variations with the temperature on multi-decadal timescales. Our results also show that temperature variability on the NTP has a strong linkage with the strength of the Indian summer monsoon (ISM), with the warm and cool phases of NTP temperature associated with strong and weak ISM, respectively.

Reconstruction of biological drought conditions during the past 2847 years in an alpine environment of the northeastern Tibetan Plateau, China, and possible linkages to solar forcing

In this study we reconstructed the moisture condition of the eastern Qaidam Basin of the northeastern Tibetan Plateau based on a 3585-year tree ring chronology. The growth environment of Qilian juniper (Sabina przewalskii Kom.) on the mountains in the eastern Qaidam Basin was first determined by comparing precipitation and temperature estimates from two spatial datasets (PRISM and World Climate). Moisture balance was calculated as the sum of simulated moisture deficit (negative) and surplus using a modified Thornthwaite water balance model, and used as a proxy of biological drought conditions. Using data during 1956–2005, we established the transfer function to reconstruct a 2847-year series of January–June moisture balance (843 BCE–2004 CE). With an adjusted R2 value of 0.654 of the transfer function and strong performance in validation, the reconstructed January–June moisture balance can be considered an excellent indicator of biological drought conditions for the study region. The reconstructed series showed strong correlations with reconstructed PDSI in the monsoon Asian region, representing a region of 10° latitudes by 20° longitudes. Using the reconstructed series, we identified centennial-scale dry periods since 843 BCE: 381–277 BCE, 425–520 CE, 1108–1212 CE, 1428–1516 CE, and 1634–1743 CE. Additionally it had statistically significant negative correlations with a monsoon intensity proxy based on oxygen stable isotope from southwestern China (Dongge Cave). Further analyses identified significant relationships with solar activity, especially during the last 700years. We confirmed the ~200-year cyclic pattern in the reconstructed moisture balance series, which matched the known 210-year de Vries solar cycle and peaked during the Little Ice Age. However, the cyclic patterns of the reconstructed moisture balance series and solar activity were decoupled for the period prior to approx. 1300 CE.

Growth–climate relationships along an elevation gradient on a southeast-facing mountain slope in the semi-arid eastern Qaidam Basin, northeastern Tibetan Plateau

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. Several recent studies across the Tibetan Plateau found consistent growth–climate relations at all elevations from the lower treelines to the upper treelines. These findings seem to challenge the general principle of dendroclimatology that precipitation serves as the controlling factor of radial tree growth at lower elevations while temperature serves as the controlling factor at higher elevations in semi-arid regions. Such conclusions also question the potential of temperature reconstruction using ring-width data in these regions if precipitation remains the dominant factor of tree growth at the upper treelines. In this study, radial growth of Qilian juniper (Sabina przewalskii Kom.) was examined along an elevation gradient between ~3820 and 4230 m in the mountains east of the Qaidam Basin, northeastern Tibetan Plateau, to determine the limiting factors of radial tree growth at different elevations. Rotated principal component analysis revealed two modes of variation patterns. The first mode presents mostly tree ring data from the lower elevation zones (3820–4100 m) and contains strong signals of precipitation variation. The second mode represents the higher elevation zones (approx. 4100–4230 m) and contains strong signals of both temperature and precipitation variations. When signals of precipitation variation are removed from the tree ring data using partial correlation, the growth–temperature relationships become more evident on the upper slope. When correlations between individual tree-ring series and climate variables were examined, we discovered that there were better chances of finding tree ring samples strongly correlated to temperature variables (r = 0.6 or higher) at the elevation zone within ~100 m of the upper treeline, but uncommon at lower elevations. We also found that topographic variables, such as slope gradient and growing-season direct solar radiation may have minor influences on the growth–climate relationships.

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.

Tree-ring-based reconstruction of temperature variability (1445–2011) for the upper reaches of the Heihe River Basin, Northwest China

Long-term temperature variability has significant effects on runoff into the upper reaches of inland rivers. This paper developed a tree-ring chronology of Qilian juniper (Sabina przewalskii Kom.) from the upper tree-line of the middle Qilian Mountains within the upper reaches of Heihe River Basin, Northwest China for a long-term reconstruction of temperature at the study site. In this paper, tree-ring chronology was used to examine climate-growth associations considering local climate data obtained from Qilian Meteorological Station. The results showed that temperatures correlated extremely well with standardized growth indices of trees (r=0.564, P<0.001). Tree-ring chronology was highest correlated with annual mean temperature (r=0.641, P<0.0001). Annual mean temperature which spans the period of 1445–2011 was reconstructed and explained 57.8% of the inter-annual to decadal temperature variance at the regional scale for the period 1961–2011. Spatial correlation patterns revealed that reconstructed temperature data and gridded temperature data had a significant correlation on a regional scale, indicating that the reconstruction represents climatic variations for an extended area surrounding the sampling sites. Analysis of the temperature reconstruction indicated that major cold periods occurred during the periods of 1450s–1480s, 1590s–1770s, 1810s–1890s, 1920s–1940s, and 1960s–1970s. Warm intervals occurred during 1490s–1580s, 1780s–1800s, 1900s–1910s, 1950s, and 1980s to present. The coldest 100-year and decadal periods occurred from 1490s–1580s and 1780s–1800s, respectively, while the warmest 100 years within the studied time period was the 20th century. Colder events and intervals coincided with wet or moist conditions in and near the study region. The reconstructed temperature agreed well with other temperature series reconstructed across the surrounding areas, demonstrating that this reconstructed temperature could be used to evaluate regional climate change. Compared to the tree-ring reconstructed temperature from nearby regions and records of glacier fluctuations from the surrounding high mountains, this reconstruction was reliable, and could aid in the evaluation of regional climate variability. Spectral analyses suggested that the reconstructed annual mean temperature variation may be related to large-scale atmospheric–oceanic variability such as the solar activity, Pacific Decadal Oscillation (PDO) and El Niño–Southern Oscillation (ENSO).

Closed Lake oxygen isotope records of drought in the Pacific Northwest Spanning the common era

For the mechanistic understanding of hydroclimate variability, stable oxygen isotopic ratios (δ18O) of tree-ring α-cellulose can play a key role in paleoclimatic research. On the north-east Tibetan Plateau (TP), a region particularly sensitive to climate change, there exists a distinct lack of δ18O research in tree-ring archives. The few currently existing tree-ring δ18O chronologies were obtained by pooling the wood material from the same year from different trees prior to preparation and analysis. Although this method is time and cost efficient, it might impede the analysis of changes within the internal variability of oxygen isotope signals and a deeper understanding of the resulting climate reconstruction. We selected five Qilian juniper (Sabina przewalskii Kom.) trees covering the period 1951–2011 on the north-east TP to investigate the climate signals contained in stable oxygen isotopic composition records obtained using single tree analysis. Although the inter-series correlation between the five individual δ18O series indicates a highly significant relationship (mean r = 0.59, n = 59, p = 0.01), the five individual δ18O series show significantly differently mean values. We found significant negative correlations between drought/hydroclimatically triggered climate parameters (PDSI, precipitation) and each of the individual δ18O series. Spatial correlation maps indicate negative correlation of tree-ring δ18O and Indian Ocean sea surface temperatures, and inverse correlation patters of moisture conditions on the northern and southern TP. Our results provide a reference for future research on stable oxygen isotope/climate signals in the species S. przewalskii Kom..

Drought signals in tree-ring stable oxygen isotope series of Qilian juniper from the arid northeastern Tibetan Plateau

For the mechanistic understanding of hydroclimate variability, stable oxygen isotopic ratios (δ18O) of tree-ring α-cellulose can play a key role in paleoclimatic research. On the north-east Tibetan Plateau (TP), a region particularly sensitive to climate change, there exists a distinct lack of δ18O research in tree-ring archives. The few currently existing tree-ring δ18O chronologies were obtained by pooling the wood material from the same year from different trees prior to preparation and analysis. Although this method is time and cost efficient, it might impede the analysis of changes within the internal variability of oxygen isotope signals and a deeper understanding of the resulting climate reconstruction. We selected five Qilian juniper (Sabina przewalskii Kom.) trees covering the period 1951–2011 on the north-east TP to investigate the climate signals contained in stable oxygen isotopic composition records obtained using single tree analysis. Although the inter-series correlation between the five individual δ18O series indicates a highly significant relationship (mean r=0.59, n=59, p=0.01), the five individual δ18O series show significantly differently mean values. We found significant negative correlations between drought/hydroclimatically triggered climate parameters (PDSI, precipitation) and each of the individual δ18O series. Spatial correlation maps indicate negative correlation of tree-ring δ18O and Indian Ocean sea surface temperatures, and inverse correlation patters of moisture conditions on the northern and southern TP. Our results provide a reference for future research on stable oxygen isotope/climate signals in the species S. przewalskii Kom..

Responses of pigmentation and δ13C in Qilian juniper to cold and drought stresses under natural conditions in the Qilian Mountains, China

The seasonal changes of pigments and stable carbon isotope composition (δ13C values) were investigated in needles of Qilian juniper (Sabina przewalskii Kom.) from two typical sites, one drier and the other wetter, in the Qilian Mountains, China. The anthocyanins and rhodoxanthin content from both sites were much higher in winter than in summer. Plant needles contained more carotenoids and xanthophylls in winter at the wetter site, while no seasonal difference appeared at the drier site. However, lower chlorophyll content and higher proline and δ13C were observed at the drier site. Average tree height was shorter at the drier site trees than at the wetter site. Our results suggested that under natural conditions, pigmentation in S. przewalskii may serve to improve the energy balance of the photosynthetic apparatus under cold and drought stresses. Proline and δ13C could be used as drought indicators for S. przewalskii.

Intra-annual stem radial increment response of Qilian juniper to temperature and precipitation along an altitudinal gradient in northwestern China

Spring temperature is a major limiting factor at the beginning of the growing season, the timing of growth initiation can increase by about 7 days/°C. During the growing season, impacts of climate variables on radial growth are similar along an altitudinal gradient. Altitude is considered as an important factor affecting tree growth in mountain forest ecosystems. In this paper, the results of a 2-year field study along an altitudinal gradient in the cold and arid central Qilian Mountains, northwestern China, are reported. Twelve Qilian juniper trees (Sabina przewalskii Kom.) were monitored with high-resolution dendrometers at three altitudes ranging from 2,865 to 3,550 m. At each altitude, a local weather station was installed close to the studied trees. We identified correlations between intra-annual growth patterns derived from the Gompertz equation with local air temperature and precipitation data. The timing of growth initiation became earlier and the growing season duration increased with decreasing altitude. The onset of radial growth occurred between early May and early June, and the growing season terminated between mid-July and late August, resulting in a growing season duration that decreased from 107 to 41 days as elevation increased. June is the most important growth period at each altitude. Spring temperature, which is strongly associated with elevation, is a critical factor determining the initiation of radial growth. The timing of growth initiation was delayed by 3–4 days per 100 m elevation. When associated with the modeled altitudinal spring temperature lapse rate of −0.48 °C/100 m, the onset of the growing season increased by about 7 days/°C. However, during the growing season, daily stem radial increments showed a positive correlation with precipitation and a negative correlation with daily maximum air temperature at all altitudes. Our study provides new data revealing the basic growth processes of Qilian juniper trees and provides significant information to quantify the responses of tree growth to future global warming.

A comparison between medieval and current climate warming using the Przewalskii’s juniper tree-ring data

Comparison with the climate of the past centuries has demonstrated until recently the unprecedented warming at the scale of the last millennium at least. This is embodied in the latest report of the Intergovernmental Panel on Climate Change. However, recently the studies have appeared putting this statement into question. A new 1000-year long reconstruction based on the tree-ring variations of the long-living Chinese junipers (Sabina Przewalskii Kom.) growing in the northeastern part of the Tibetan Plateau reveals that the climate during and immediately after the medieval maximum of solar activity was warmer that the present-day one, all subsequent cooling coincided with the periods of low solar activity, and the warming in the 1970s–1990s followed a new maximum of the solar activity which peak fell on the 1960s.

The influences of canopy species and topographic variables on understory species diversity and composition in coniferous forests.

Understanding the factors that influence the distribution of understory vegetation is important for biological conservation and forest management. We compared understory species composition by multi-response permutation procedure and indicator species analysis between plots dominated by Qinghai spruce (Picea crassifolia Kom.) and Qilian juniper (Sabina przewalskii Kom.) in coniferous forests of the Qilian Mountains, northwestern China. Understory species composition differed markedly between the forest types. Many heliophilous species were significantly associated with juniper forest, while only one species was indicative of spruce forest. Using constrained ordination and the variation partitioning model, we quantitatively assessed the relative effects of two sets of explanatory variables on understory species composition. The results showed that topographic variables had higher explanatory power than did site conditions for understory plant distributions. However, a large amount of the variation in understory species composition remained unexplained. Forward selection revealed that understory species distributions were primarily affected by elevation and aspect. Juniper forest had higher species richness and α-diversity and lower β-diversity in the herb layer of the understory plant community than spruce forest, suggesting that the former may be more important in maintaining understory biodiversity and community stability in alpine coniferous forest ecosystems.

Climate Control on Tree Growth at the Upper and Lower Treelines: A Case Study in the Qilian Mountains, Tibetan Plateau

It is generally hypothesized that tree growth at the upper treeline is normally controlled by temperature while that at the lower treeline is precipitation limited. However, uniform patterns of inter-annual ring-width variations along altitudinal gradients are also observed in some situations. How changing elevation influences tree growth in the cold and arid Qilian Mountains, on the northeastern Tibetan Plateau, is of considerable interest because of the sensitivity of the region’s local climate to different atmospheric circulation patterns. Here, a network of four Qilian juniper (Sabina przewalskii Kom.) ring-width chronologies was developed from trees distributed on a typical mountain slope at elevations ranging from 3000 to 3520 m above sea level (a.s.l.). The statistical characteristics of the four tree-ring chronologies show no significant correlation with increasing elevation. All the sampled tree growth was controlled by a common climatic signal (local precipitation) across the investigated altitudinal gradient (520 m). During the common reliable period, covering the past 450 years, the four chronologies have exhibited coherent growth patterns in both the high- and low-frequency domains. These results contradict the notion of contrasting climate growth controls at higher and lower elevations, and specifically the assumption that inter-annual tree-growth variability is controlled by temperature at the upper treeline. It should be stressed that these results relate to the relatively arid conditions at the sampling sites in the Qilian Mountains.

Moisture variations over the past millennium characterized by Qaidam Basin tree-ring δ 18O

High-resolution tree-ring delta O-18 chronologies covering the last millennium, although scarce, are essential in understanding patterns of climatic changes in the northeastern region of the Qinghai-Tibetan Plateau. For this study, a tree-ring delta O-18 chronology with a temporal resolution of 3-years was developed from the long-lived Qilian juniper (Sabina przewalskii Kom.), extending back in time to AD 991. This long delta O-18 chronology was significantly correlated with the yearly delta O-18 in tree rings during the common period from 1800 to 2006, and was an effective proxy for relative humidity during the growing season. A low-frequency moisture pattern signified the occurrence of a slight drought during the Medieval Climate Anomaly, a marked occurrence of a wet period during the Little Ice Age, and a trend in increasing moisture levels, although lower than average, alongside the Twentieth Century warming trend. Comparisons to other hydroclimatic reconstructions indicate that this tree-ring delta O-18 chronology serves as a reliable paleo-humidity proxy for the Qaidam Basin as well as documenting details of past humidity levels in the region.

Two phases of seasonal stem radius variations of Sabina przewalskii Kom. in northwestern China inferred from sub-diurnal shrinkage and expansion patterns

In the National Natural Reserve of the Qilian Mountains, northwest China, automated dendrometers were installed on Qilian juniper (Sabina przewalskii Kom.) in 2010. Here, we present a complete 1-year data series of dendrometer measurements and synchronous meteorological records. The mean daily radius change index curve obtained by first-difference standardization was analyzed. The results indicate strong similarities of stem radius variations among the studied trees. By graphical inspection of sub-diurnal shrinkage and expansion patterns, seasonal stem radius variations could be divided into two general phases. During early winter to spring, daily amplitudes show strong fluctuations, and meteorological data indicate that both air and soil temperatures are positively related to stem radius swelling. From late March to early November 2011, stem radius expansion is negatively related to both air and soil temperatures, as well as to vapor pressure deficit, and positively related to precipitation and soil moisture. We found that the dividing lines between the two phases were strongly linked to the occurrence of a 0 °C daily mean air temperature, indicating that air temperature played an important effect on stem radius variations in this cold and arid environment. During the growing season in 2011, May and June are the most productive months.

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.

Extreme drought events in the years 1877–1878, and 1928, in the southeast Qilian Mountains and the air–sea coupling system

Droughts events have long-lasting effects on economic and social activities, particularly in the semi-arid region of northern China. In this study, four tree ring-width chronologies were developed based on lived Qilian Juniper (Sabina przewalskii Kom.) trees in the southeast Qilian Mountains, China. The four chronologies were developed from 164 cores (82 trees) for the northern marginal of the Asian summer monsoon in China. Tree growth of this area is sensitive to moisture variability of the growth season. During the last 260 years, there had been extreme growth depressions in the years 1877-1878 and 1928, indicating large-scale droughts had occurred in the study area. These extreme drought events had a devastating effect not only on hydrology and agriculture, but also on society and economics. Extreme droughts in 1877-1878 and in 1928 occurring in the study region and most of China were triggered by different climate regimes. The former drought distribution pattern was probably attributable to El Nifio events, while the latter was associated with warm and cold air masses. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.