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To provide a long-term context for understanding the “Karakoram Anomaly” in recent glacier studies, we originally aimed to develop an annually resolved multi-century winter–spring precipitation record using tree-ring earlywood cellulose δ18O (δ18OEW) of Pinus wallachina from the Karakoram, northern Pakistan. Out of expectation, winter (January–May) temperature rather than precipitation is found to be the dominant climate signal (r = 0.63, p

Understanding synergies and trade-offs of ecosystem services (ESs), finding influencing factors related to these ESs, and determining how these factors regulate spatiotemporal patterns are vital to the sustainability of ecosystem management. However, the spatialization of the correlation between the relationships among ESs and the influencing factors has remained a difficult analysis for the Qinghai-Tibet Plateau (QTP). Consequently, three ESs are quantified using different models, and synergies and trade-offs among the ESs are analyzed. The precipitation changes, minimum temperature changes, gross domestic product changes, population changes, normalized difference vegetation index (NDVI) changes, and the digital model (DEM) were selected as influencing factors. The influence of these influencing factors on the relationship among the ESs was then measured using the methods of logistic regression (LR) and the geographically weighted logistic regression (GWLR). The authors showed that (1) the spatially concordant high supplies of water yield (WY) and carbon storage (CS) were distributed in the southeastern forest areas and the eastern grassland areas, whereas high meat supply (MS) was primarily distributed in the eastern and the middle of the grassland areas. (2) The relationships between the WY and MS and between the CS and MS were primarily trade-offs, and their area ratios were 40% and 41%, respectively. However, the relationship between the WY and CS was primarily synergistic, and the area ratio was 54%. (3) Precipitation was more highly related to the relationships among the ESs than the other influencing factors among the six independent variables. Compared to the LR, the GWLR model provides an improved calculation to explain the correlation between the relationships among the ESs and these influencing factors. Overall, it was found that these influencing factors on the impacts of the relationship among the ESs were different, and they lacked spatial concordance. These results highlight the importance of managing nearly all areas by specifically controlling local factors.

Warming-induced drought stress leads to convergent and negative growth responses to temperature between sympatric tree species, implying an increasing interspecific competition for soil moisture. In mixed forests, sympatric tree species avoid competition by partitioning their niches according to available environment resources. We raise the hypothesis that climate warming leads to a convergence in growth responses to climate, thus increasing the competition among sympatric species in drought-prone forests. In this study, we selected a mixed forest located at ca. 3600 m a.s.l in the Baima Snow Mountains, an inner dry valley of the southeastern Tibetan Plateau. We measured width of the tree rings produced during 1910–2016 in 60 trees belonging to three sympatric species: Abies georgei, Picea likiangensis, and Betula delavayi. We analyzed the changes in radial growth and their responses to climate. We detected shifts in the responses to climate after the 1990s. The radial growth of all species was positively correlated with precipitation from 1964 to 1990, but negatively correlated with March–June temperature from 1991 to 2016. Compared to the period 1964–1990, convergent and negative growth responses to warmer temperatures in the period 1991–2016 probably reflect less available soil moisture for growing in this mixed forest. We conclude that climate warming will affect the niches of sympatric species in mixed forests subjected to seasonal drought, thus increasing competition and altering structure and composition of the stands in dry regions.

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.

Large tropical volcanic eruptions can cause short-term global cooling. However, little is known whether large tropical volcanic eruptions, like the one in Tambora/Indonesia in 1815, cause regional hydroclimatic anomalies. Using a tree-ring network of precisely dated Himalayan birch in the central Himalayas, we reconstructed variations in the regional pre-monsoon precipitation back to 1650 CE. A superposed epoch analysis indicates that the pre-monsoon regional droughts are associated with large tropical volcanic eruptions, appearing to have a strong influence on hydroclimatic conditions in the central Himalayas. In fact, the most severe drought since 1650 CE occurred after the Tambora eruption. These results suggest that dry conditions prior to monsoon in the central Himalayas were associated with explosive tropical volcanism. Prolonged La Nina events also correspond with persistent pre-monsoon droughts in the central Himalayas. Our results provide evidence that large tropical volcanic eruptions most likely induced severe droughts prior to monsoon in the central Himalayas.

Most Tibetan people make their living through pastoralism, with livestock grazing being widespread throughout the Tibetan Plateau. The Tibetan Plateau is also home to the northern hemisphere’s highest treelines but the effects of human activities, in particular pastoralism, on these treelines and their influence on the treeline responses to climate change remain unclear. To disentangle the effects of pastoral disturbances and climate on treeline dynamics, we surveyed three plots at grazing-disturbed Balfour spruce (Picea likiangensis var. balfouriana) treelines in the Yushu region (eastern Tibetan Plateau) and compared this data with published results of five undisturbed spruce treeline sites. Spatiotemporal changes in the position and structure of treelines during the past 400 years were reconstructed using dendrochronology. Tree recruitment was significantly linked to long-term summer and winter temperature. Under low local population densities and grazing pressure but consistent climate warming, disturbed treelines shifted upwards by 23.9–82.6 m during the 1611–1910 period. However, under higher local population densities, increased grazing pressure and climate warming over the last century, disturbed treelines showed no significant upward shift. In contrast, undisturbed treelines shifted upward by 25–68.5 m over the last century, thus implying that pastoralism was suppressing treeline expansion in disturbed sites. Together, these results underscore the importance of anthropogenic disturbances in influencing the structure and position of alpine treelines on the Tibetan Plateau. The role played by human disturbance should be carefully considered when evaluating the potential for treeline advance under future climate warming.

Climatic change is exhibiting significant effects on the ecosystem of the Tibetan Plateau (TP), a climate-sensitive area. In particularly, winter frost, freezing events and snow avalanche frequently causing severe effects on ecosystem and social economy, however, few long-term winter temperature records or reconstructions hinder a better understanding on variations in winter temperature in the vast area of the TP. In this paper, we present a minimum winter (November–February) temperature reconstruction for the past 668 years based on a tree-ring network (12 new tree-ring chronologies) on the southeastern TP. The reconstruction exhibits decadal to inter-decadal temperature variability, with cold periods occurring in 1423–1508, 1592–1651, 1729–1768, 1798–1847, 1892–1927, and 1958–1981, and warm periods in 1340–1422, 1509–1570, 1652–1728, 1769–1797, 1848–1891, 1928–1957, and 1982–2007. As suggested by the comparisons with existing winter temperature series and spatial correlations with Climatic Research Unit gridded data, our reconstruction is reliable and indicative, and it can represent large-scale winter temperature variability on the southeastern TP. Furthermore, it shows an overall agreement with winter temperature from the northeastern TP on decadal to inter-decadal timescales. It also shows the possible effects of volcanic eruption and reducing solar activity on the winter temperature variability for the past six centuries on the southeastern TP.

The Tibetan Plateau and its surrounding mountains exhibit the largest concentration of glaciers at lower latitudes on earth, providing source water for the large river systems in Asia. However, glacier observations in this region are short and scarce and hence limit a better understanding of glacier behaviors under a warming climate and thereto coupled processes. The purpose of this research is to investigate the potential and the uncertainty for using pioneering trees on glacial deposits/glacier forefields as a proxy record for past glacier fluctuations in the Himalaya-Nyanqentanggula-Hengduan (H2N) area. It was found that Hippophae tibetana spent 4 years to colonize the glacier forefields at Hailuogou glacier and Pinus wallichiana germinated 11 years after glacier retreating at Gangapuna and Raikot glaciers. At deposit sites of glacier avalanche and glacial lake outburst, it took 8 years for Larix griffithii to germinate after the historical events. As shown by bootstrap resampling, the precision of the sampled maximum tree age could reach 2–14 years, which is related to the sample size to ensure the possibility of obtaining the eldest trees. However, if using the traditional sampling method at 100-cm height, errors of tree age estimation may reach up to ±20 years due to uncertainties of pith offset estimation and height-age calibration. If samples are collected with pith from ≤20 cm tree height, an error of

Alpine biomes are climate change hotspots, and treeline dynamics in particular have received much attention as visible evidence of climate-induced shifts in species distributions. Comparatively little is known, however, about the effects of climate change on alpine shrubline dynamics. Here, we reconstruct decadally resolved shrub recruitment history (age structure) through the combination of field surveys and dendroecology methods at the world’s highest juniper (Juniperus pingii var. wilsonii) shrublines on the south-central Tibetan Plateau. A total of 1,899 shrubs were surveyed at 12 plots located in four regions along an east-to-west declining precipitation gradient. We detected synchronous recruitment with 9 out of 12 plots showing a gradual increase from 1600 to 1900, a peak at 1900–1940, and a subsequent decrease from the 1930s onward. Shrub recruitment was significantly and positively correlated with reconstructed summer temperature from 1600 to 1940, whereas it was negatively associated with temperature in recent decades (1930–2000). Recruitment was also positively correlated with precipitation, except in the 1780–1830 period, when a trend toward wetter climate conditions began. This apparent tipping point in recruitment success coincides with a switch from positive to negative impacts of rising temperatures. Warming-induced drought limitation has likely reduced the recruitment potential of alpine juniper shrubs in recent decades. Continued warming is thus expected to further alter the dynamics of alpine shrublines on the Tibetan Plateau and elsewhere.

Phylogenetic studies on the leaf unfolding date are expected to improve understanding of phenological change. However, it remains unclear whether the response of leaf unfolding date to temperature is phylogenetically conserved among close relatives across differential and harsh habitats. Meanwhile, the phenological mechanism underlying the role of phylogenetic relationship on plant phenology remains unclear. We used Blomberg's K to assess phylogenetic signal in leaf unfolding date, its sensitivities to daily mean, minimum and maximum temperatures, in growing-degree-days and average level of each of daily mean, minimum and maximum temperatures experienced by plants over a given period prior to leaf unfolding date for eighteen species at seventeen sites in the Tibetan Plateau. We showed that leaf unfolding date and its sensitivities to daily mean, minimum and maximum temperatures did not exhibit overall significant phylogenetic signals. Moreover, the sensitivity of leaf unfolding date to daily minimum temperature exhibited phylogenetic antisignal at species level, which indicated the trait difference among close relatives exceed that among distantly related lineages. However, there were overall significant phylogenetic signals in growing-degree-days and the average level of each of daily mean, minimum and maximum temperatures experienced by plants before leaf unfolding date. The signals were stronger for the growing-degree-days and the average level of each of daily mean, minimum and maximum temperatures in the period closer to leaf unfolding date. Our results imply that close relatives trace similar heat requirements for leaf unfolding date in the harsh and spatially heterogeneous environment of the Tibetan Plateau. However, the time when these lineage-specific heat requirements are met varies spatially depending on local conditions, thereby resulting in phylogenetic non-conservatism of leaf unfolding date and its temperature sensitivities. This provides a phenological explanation, for the first time, for phylogenetic non-conservatism in plant leafing phenology.

Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesized that there is a critical minimum temperature (CTmin) preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir (Abies georgei var. smithii) treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature (CTmin) for the onset and end of xylogenesis occurred at 0.7 ± 0.4 °C. A process-based modelling chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.

Little is known about whether increasing iWUE (intrinsic water use efficiency) can stimulate tree growth in the temperature-limited natural timberlines. Here, we presented the basal area increment (BAI) and iWUE chronologies of Smith fir ( Abies georgei var. smithii ) from 1900 to 2006 at a high-elevation (ca. 4400 m a.s.l.) timberline in the humid Sygera Mountains, southeastern Tibetan Plateau (TP). The commonality analysis model was applied to investigate the relationships among BAI, temperatures, atmospheric CO 2 concentration ( C a ) and iWUE during 1961–2006, taking into account of both pure and joint effects. As illustrated by the commonality analysis model, the pure effect of C a (39.15%) had more stronger influence on iWUE than that of the Tmean (annul mean temperature, 0.12%), but the joint effect between C a and Tmean (49.79%) on iWUE was stronger than any pure effect for the raw data with an increasing trend. For the first-difference data with year-to-year variations, the pure effect of C a (7.72%) on iWUE was stronger than that of Tmean (0.59%) and the joint effect between them (0.59%). All above imply the C a is the dominant factor for iWUE both for the 46-year trend and interannual variations. In addition, as showed by the commonality analysis model, the pure effect of iWUE (17.57%) played a much more important role on BAI than that of temperatures (smt, mean temperature during June, July, August of current year, 5.92%; amt, mean temperature during September, October, November of previous year, 3.04%), while joint effects of iWUE and temperatures contributed more (27.96%; 13.90%; 16.47%) to the BAI than their pure effects for the raw data with an increasing linear trend. For the first-difference data with interannual variations, the pure effect of smt (12.45%) had much more effect on BAI than that of iWUE (5.49%), at the same time the joint iWUE and temperatures contributed less (3.56%; 1.9%; 1.31%) to the BAI than their pure effects. These results suggest that an increasing iWUE could enhance 46-year increasing tree growth trend at humid and high-elevation timberlines, supporting the CO 2 fertilization hypothesis, while temperatures dominate the interannual variations of tree growth.

Moderate-severity fire disturbances can accelerate upslope shifts of alpine treelines by reducing interspecific interactions, providing additional evidence for the species interaction mechanism in controlling treeline dynamics. Biotic interactions between trees and other plants may modulate the responses of alpine treelines to climate. Moderate disturbances could, therefore, accelerate upward shifts of alpine treelines as the climate warms by reducing the coverage of competitor plants and resetting interspecific interactions. Larch (Larix potaninii var. macrocarpa) treelines disturbed by fire on the southeastern Tibetan Plateau are good locales for testing this hypothesis. We characterized treelines in five large rectangular plots spanning undisturbed and fire-disturbed fir (Abies georgei) and larch treelines. The fires in the 1960s caused gaps in the reconstructed age structures of the larches during the 1970s but did not lead to downslope shifts in treeline position. Recruitment has instead increased since the 1980s within the disturbed larch treelines, with treelines shifting upward by 11–44 m. In contrast, the undisturbed larch and fir treeline positions remained mostly unchanged. We hypothesize that upslope shifts of alpine treelines are likely a consequence of climatic warming, but fire disturbances can accelerate these dynamics by altering interspecific interactions.

Alpine biomes are climate change hotspots, and treeline dynamics in particular have received much attention as visible evidence of climate-induced shifts in species distributions. Comparatively little is known, however, about the effects of climate change on alpine shrubline dynamics. Here, we reconstruct decadally resolved shrub recruitment history (age structure) through the combination of field surveys and dendroecology methods at the world's highest juniper (Juniperus pingii var. wilsonii) shrublines on the south-central Tibetan Plateau. A total of 1,899 shrubs were surveyed at 12 plots located in four regions along an east-to-west declining precipitation gradient. We detected synchronous recruitment with 9 out of 12 plots showing a gradual increase from 1600 to 1900, a peak at 1900-1940, and a subsequent decrease from the 1930s onward. Shrub recruitment was significantly and positively correlated with reconstructed summer temperature from 1600 to 1940, whereas it was negatively associated with temperature in recent decades (1930-2000). Recruitment was also positively correlated with precipitation, except in the 1780-1830 period, when a trend toward wetter climate conditions began. Warming-induced drought limitation has likely reduced the recruitment potential of alpine juniper shrubs in recent decades. Ongoing warming without a simultaneous increase in precipitation is expected to further impair recruitment at the world's highest juniper shrublines and alter the dynamics and competitive balance between woody plant species throughout these alpine biomes.

Shrub willows (Salix species) are widespread beyond the latitudinal and altitudinal treelines. Their ring width has been shown to be a reliable ecological indicator for changes in the harsh cold conditions in the Arctic, but little is known on their growth in alpine conditions. The shrubby Salix oritrepha grows above the treeline on the northeastern Tibetan Plateau (TP), making it an interesting woody species to explore responses of alpine communities to ongoing climate warming in this area. Since precipitation increases with increasing elevation (until 4670 m) in the study area, we hypothesize that the growth of S. oritrepha is mainly constrained by cold summer temperature. We sampled 35 S. oritrepha individuals above the juniper treeline (4200 m), and took basal wood cross sections for dendrochronological analyses. Few missing rings were detected at the shoot base when serial sectioning was applied. Ring width (RW) and basal area increment (BAI) standard chronologies were established. We found ...

The threshold minimum air temperature driving xylem growth of alpine Rhododendron aganniphum is lower than that commonly observed at the treeline of conifers. Understanding how alpine shrubs grow and which environmental factors drive their biomass gain could help to functionally differentiate trees and shrubs. The cambium is the main meristem responsible for wood formation in trees and shrubs. Thus, a better knowledge of cambium growth dynamics in alpine shrubs would allow explaining why shrubs displace trees above the treeline. Here, we aim to investigate the timings and dynamics of xylogenesis and to identify the thermal thresholds controlling the onset of xylem growth of Rhododendron aganniphum, a tall shrub growing above the alpine treeline on the Tibetan Plateau. Timings of xylogenesis and radial growth rates were assessed from anatomical observations of the developing xylem during three growing seasons (2011, 2012, and 2013). The threshold temperature at which xylogenesis had a 0.5 probability of being active was calculated with logistic regressions. The onset of xylogenesis was observed between mid and late June, whereas the end of xylogenesis lasted from mid to late September. Overall, the duration of xylem growth lasted 88–101 days, and 94 % of the ring was formed from June to August. The threshold for the onset of xylem growth was observed at 2.0 ± 0.6 °C for the minimum air temperature, lower than that commonly observed for treeline conifers (ca. 6 °C). This low thermal threshold allows alpine shrubs to have a growing season long enough to complete xylem production and maturation during the warmest summer months. Our results suggest that the time required to complete xylogenesis is critical to understand why shrubs displace trees above the treeline.

Climate warming has induced substantial advances in the onset of vegetation green-up in the northern hemisphere during recent decades. To date, however, the temporal changes in green-up date have not been adequately explained by the statistical relationships between green-up date and climatic factors, posing challenges in the attribution and prediction of phenological change. In this study, we thus turned to focus on autumn phenology, a critical biotic factor that is likely to affect the subsequent spring phenology of vegetation. Using satellite-retrieved start and end of growing season (SOS and EOS) over the period from 1982 to 2015, we examined the association between the EOS and the SOS in the following year in northern middle and high latitudes (north of 25°N). Interannual changes in SOS were significantly (P

Understanding how severe disturbances affect forest dynamics is fundamental in ecology, conservation and management. Earthquakes of large magnitude severely impact mountain landscapes, causing strong disturbances on forests. However, it is unknown how the resilience of tree growth after strong earthquakes changes as a function of site factors as elevation. Herein, we investigated the radial-growth responses of surviving trees after the 1950-Zayu-Medog MW 8.6 earthquake which devastated the southeastern Tibetan Plateau. We reconstructed radial growth dynamics of Abies delavayi var. motuoensis after 1950 in six sites selected along an elevational transect located in the Medog valley. Post-earthquake growth responses were detected among 60% of sampled trees in the period 1950–1955, but these responses varied depending on site elevation. Trees at the alpine treeline were less disturbed compared to those located at mid and low elevations. Severe growth suppressions, including the formation of missing rings, occurred during the first three years after the earthquake, and were stronger at low elevations. Growth releases mostly occurred after 1954. Long-term growth release, lasting more than ten years, was mainly observed at low elevations, near talus fans prone to landslides and rock falls. Growth rates returned to pre-earthquake values 45 years after the earthquake occurrence. Our results evidence how tectonic influences on tree growth depend on local factors as elevation, and demonstrate that tree resilience after severe geo-hazards is contingent on site conditions.

Impacts of climatic means on spring phenology are well documented, whereas the role of climatic variance, such as occurrence of spring frosts, has long been neglected. A large elevational gradient of forests on the southeastern Tibetan Plateau provides an ideal platform to explore correlates of spring phenology and environmental factors. We tested the hypothesis that spring frost was a major factor regulating the timing of bud-leaf phenology by combining 5 years of in situ phenological observations of Abies georgei var. smithii with concurrent air temperature data along two altitudinal gradients. Mean lapse rate for the onset of bud swelling and leaf unfolding was 3.1 ± 0.5 days/100 m and 3.0 ± 0.6 days/100 m, respectively. Random forest analysis and conditional inference trees revealed that the frequency of freezing events was a critical factor in determining the timing of bud swelling, independent of topographic differences, varying accumulation of chilling days, and degree-days. In contrast, the onset of leaf unfolding was primarily controlled by the bud swelling onset. Thus, the timing of bud swelling and leaf unfolding appear to be controlled directly and indirectly, respectively, by spring frost. Using space-for-time substitution, the frequency of spring freezing events decreased by 7.1 days with 1 °C of warming. This study provides evidence for impacts of late spring frosts on spring phenology, which have been underappreciated in research on phenological sensitivity to climate but should be included in phenology models. Fewer spring freezing events with warming have important implications for the upward migration of alpine forests and treelines.

Climate warming is significantly affecting the composition and function of forest ecosystems. However, the forest responses to climate change in sub-humid and temperate areas are understudied compared with cold and semi-arid areas. Here, we investigate the radial-growth responses of two subalpine conifer species along an elevational gradient located in the Qinling Mountains, a sub-humid and temperate area situated in central China. Three sites dominated by larch (Larix chinensis Beissn.) and two other sites dominated by fir (Abies fargesii Franch.) located at different elevations were sampled. L. chinensis at a higher elevation showed more common and stronger climatic signals than A. fargesii at a lower elevation. The radial growth of L. chinensis was limited by low pre-growing season temperatures and showed an increasing growth trend in the last few years. On the other hand, A. fargesii growth was limited by summer water shortage and it was characterized by a declining trend in the most recent decade. Consequently, L. chinensis would benefit from climate warming, whereas A. fargesii could be regarded as a vulnerable tree species to warming-induced drought stress., This work was funded by the National Natural Science Foundation of China (41601192 and 41525001), and China Postdoctoral Science Foundation (2015M572591). J.J.C. thanks the support of the CGL2015-69186-C2-1-R project (Spanish Ministry of Economy).

Background and aims The onset of xylogenesis plays an important role in tree growth and carbon sequestration, and it is thus a key variable in modelling the responses of forest ecosystems to climate change. Temperature regulates the resumption of cambial activity, but little is known about the effect of water availability on the onset of xylogenesis in cold but semi-arid regions. Methods The onset of xylogenesis during 2009-2014 was monitored by weekly microcoring Juniperus przewalskii trees at upper and lower treelines on the north-eastern Tibetan Plateau. A logistic regression was used to calculate the probability of xylogenic activity at a given temperature and a two-dimensional reverse Gaussian model to fit the differences between the observed and estimated days of xylogenesis onset at given temperatures and precipitation within a certain time window. Key results The thermal thresholds at the beginning of the growing season were highly variable, suggesting that temperature was not the only factor initiating xylem growth under cold and dry climatic conditions. The onset of xylogenesis was well predicted for climatic thresholds characterized by a cumulative precipitation of 17.0 ± 5.6 mm and an average minimum temperature of 1.5 ± 1.4 °C for a period of 12 d. Conclusions Xylogenesis in semi-arid regions with dry winters and springs can start when both critical temperature and precipitation thresholds are reached. Such findings contribute to our knowledge of the environmental drivers of growth resumption that previously had been investigated largely in cold regions without water shortages during early growing seasons. Models of the onset of xylogenesis should include water availability to improve predictions of xylem phenology in dry areas. A mismatch between the thresholds of temperature and moisture for the onset of xylogenesis may increase forest vulnerability in semi-arid areas under forecasted warmer and drier conditions.

Field survey methods influence the assessment of treeline structure and inferences on reconstructed treeline dynamics. Numerous field studies have described the structure of alpine treeline ecotones encompassing the forest limit and treeline to infer their dynamics in response to climate warming. However, the inferred treeline dynamics may be biased due to the selection of different plot sizes and shapes. Rectangular large plots including the whole treeline ecotone, i.e., encompassing the forest limit and the treeline, and square small plots located at current treeline have been widely used. Nevertheless, little is known about how large a plot must be to capture the main features of treeline structure and dynamics. Here, we investigate this question at Smith fir treelines located in the Sygera Mountains, southeastern Tibetan Plateau. Six rectangular large treeline plots (30 × 150 m) were sampled and compared with six square small treeline plots (30 × 30 m). Six rectangular plots with lengths shorter than the treeline ecotone span (100–135 m) were also sampled and compared with the other two plot types. Dendrochronology was used to reconstruct the recruitment dynamics of treelines, which were related to summer mean minimum temperatures. Rectangular large plots better captured the main features of recent treeline dynamics such as the abundance of recruits from the 1950s onwards and the establishment of old trees. Therefore, large plots allowed reaching more robust conclusions on treeline dynamics as compared to small plots. On the other hand, smaller rectangular plots revealed similar findings to those inferred from large rectangular plots but with a much lower survey cost. We propose using smaller rectangular plot with its longest side being shorter than the ecotone span as the most reliable and practical method to characterize alpine treeline dynamics.

Semi-arid forests at the limit of their existence close to the Gobi Desert in Inner Asia might be vulnerable to warming-induced drought stress. Yet, not much is known about the impact of global-change-type droughts on these forests. Here, we show that warming-related tree mortality is recently taking place in high-elevation semi-arid Qinghai spruce (Picea crassifolia Kom.) forests of the north-eastern margin of the Tibetan Plateau (Qilian Mountains). Tree-ring samples were collected from 24 Qinghai spruce forest plots (20 m × 20 m) at three elevations (2600, 2700, 2800 m) along eight elevation transects on north-facing slopes. Three lines of evidence suggest that these forests are increasingly at risk of increased tree mortality as a consequence of global warming, (i) a strong precipitation and air humidity dependence of radial growth, (ii) increasing frequency of missing tree rings, and (iii) a rising tree mortality rate in recent decades. The recent drought episode on the north-eastern Tibetan Plateau may represent a precursor of future global-change-type drought events in large parts of Inner Asia. Warming-related tree mortality of the semi-arid forests may be interpreted as early-warning signs for the densely populated artificial oases surrounding the Gobi Desert, which largely depend on river run-off from the mountain forests on the edge of the Tibetan Plateau.

In harsh and treeless environments, shrubs constitute the dominant growth form of woody plants, thus offering the opportunity to extend dendrochronological networks beyond the uppermost and northernmost distribution limits of trees. However, shrub-based dendrochronology has so far resulted in only a few long and climate-responsive ring-width chronologies at such stressful sites, particularly above the alpine tree line. A previous study on an alpine Rhododendron shrub species resulted in 0.85), thus representing the longest shrub chronology available to date. A principal component analysis (PCA) converted the total variability of all six site chronologies into PCs. Then, the six site chronologies and the PC1, accounting for 65.9% of the total variance of the tree-ring width, were correlated with time series of monthly climate data. Based on this, the year-to-year variability of the ring-width indices was positively correlated with July temperature, which thus turned out to be the dominant factor controlling growth. Accordingly, such long shrub-ring chronologies may act as climatic and ecological proxies in treeless environments of the Tibetan Plateau. © 2015 Collegium Boreas., This work was supported by the National Natural Science Foundation of China (41471158, 41130529), Action Plan for West Development of the Chinese Academy of Science (KZCX2-XB3-08-02). J. Julio Camarero acknowledges the ARAID Foundation for funding. We appreciate the diligent creation of the micro-sections by Sergej Kaschuro, Hamburg, and the great support for our fieldwork by the Southeast Tibet Station for Alpine Environ-ment, Observation and Research, Chinese Academy of Sciences. We thank Prof. Jan A. Piotrowski, Dr Sofia Leal and an anonymous reviewer for useful comments and suggestions that improved the manuscript.

The vast alpine grasslands of the Tibetan Plateau are lined by a belt of oroboreal coniferous forests in the transition zone to the Central Asian semi-deserts and deserts which may play important roles in the hydrology and biogeochemistry of the region. Many of these forests exist under semi-arid climates, are exposed to rapid climate warming and suffer from intensive human impact. We investigated the carbon stocks in biomass and soil in the Picea crassifolia (Qinghai spruce) forests of the Qilian Mountains, north-eastern Tibetan Plateau. In 18 forest plots at 2600–2800 m elevation, we found ecosystem carbon stocks of 348 Mg C ha−1 with carbon densities of 43 Mg C ha−1 in the live and dead aboveground biomass, 12 Mg C ha−1 in roots, 3 Mg C ha−1 in litter and 305 Mg C ha−1 in the soil (SOC; 0–100 cm). The belowground carbon pools exceed averages reported for northern boreal forests and even more clearly for zonal forest vegetation in the temperate zone. The high SOC density in the P. crassifolia forests are probably the result of slow decomposition rates due to low soil temperatures in combination with low soil moisture. The widespread degradation of mountain spruce forests to shrubland reduces the ecosystem carbon stock by >85 Mg C ha−1, and is partly caused by a 15%-reduction in SOC. We conclude that the remaining mountain forests of spruce and other conifers at the northern fringe of the Tibetan Plateau play an important role in the regional carbon budget and need urgent conservation.

Background and Aims A series of studies have shown that temperature triggers the onset of xylogenesis of trees after winter dormancy. However, little is known about whether and how moisture availability influences xylogenesis in spring in drought-prone areas. Methods Xylogenesis was monitored in five mature Qilian junipers (Juniperus przewalskii) by microcore sampling from 2009 to 2011 in a semi-arid area of the north-eastern Tibetan Plateau. A simple physical model of xylem cell production was developed and its sensitivity was analysed. The relationship between climate and growth was then evaluated, using weekly wood production data and climatic data from the study site. Key Results Delayed onset of xylogenesis in 2010 corresponded to a negative standardized precipitation evapotranspiration index (SPEI) value and a continuous period without rainfall in early May. The main period of wood formation was in June and July, and drier conditions from May to July led to a smaller number of xylem cells. Dry conditions in July could cause early cessation of xylem differentiation. The final number of xylem cells was mainly determined by the average production rate rather than the duration of new cell production. Xylem growth showed a positive and significant response to precipitation, but not to temperature. Conclusions Precipitation in late spring and summer can play a critical role in the onset of xylogenesis and xylem cell production. The delay in the initiation of xylogenesis under extremely dry conditions seems to be a stress-avoidance strategy against hydraulic failure. These findings could thus demonstrate an evolutionary adaptation of Qilian juniper to the extremely dry conditions of the north-eastern Tibetan Plateau.

Temperature is considered to be a main driver of spring phenology, whereas the role of climate extremes (such as spring frosts) has long been neglected. A large elevational gradient of mature forests on the Tibetan Plateau provides a powerful space-for-time ‘natural experiment’ to explore driving forces of spring phenology. Combining 5-yr of in situ phenological observations of Smith fir (Abies georgei var. smithii) with concurrent air temperature data along two altitudinal gradients on the southeastern Tibetan Plateau, we tested the hypothesis that spring frost was a major factor regulating the timing of spring phenology. Onset of bud swelling and leaf unfolding in the study years occurred ≈ 18 or 17 days earlier, respectively, at the lowest (3800 m a.s.l.) elevation relative to upper treelines (4360 or 4380 m a.s.l.). The frequency of freezing events and last freezing date were critical factors in determining the timing of bud swelling along two altitudinal gradients, whereas onset of leaf unfolding was primarily controlled by the onset of bud swelling. This finding provides evidence for detrimental impacts of spring frost on spring phenology, which have been underappreciated in research on phenological sensitivity to climate but should be included in phenology models. It contributes to explain the declining global warming effects on spring phenophases, because climatic extreme events (e.g. spring frosts) tend to increase with warming.

The tree-ring cellulose oxygen isotopes (δ18O) for four trees of Hippophae tibetana and four trees of Abies georgei growing in different locations around the terminal moraine in Xincuo from 1951 to 2010 were measured to explore its potential for reconstructing climatic variations in the southeastern Tibetan Plateau. The mean and standard deviation of tree-ring δ18O at different heights do not have significant differences, and there are no significant differences in the mean and standard deviation of tree-ring δ18O between trees near the brook and trees at the top of moraine, indicating that we can collect samples for tree-ring δ18O analysis regardless of sampling heights and that the micro-environment does not affect tree-ring δ18O significantly. The mean inter-series correlations of cellulose δ18O for A. georgei/H. tibetana are 0.84/0.93, and the correlation between δ18O for A. georgei and H. tibetana is 0.92. The good coherence between inter-tree and inter-species cellulose δ18O demonstrates the possibility of using different species to develop a long chronology. Correlation analysis between tree-ring δ18O and climate parameters revealed that δ18O for A. georgei/H. tibetana had negative correlations (r = −0.62/r = −0.69) with relative humidity in July–August, and spatial correlation revealed that δ18O for A. georgei/H. tibetana reflected the regional Standardized Precipitation Evapotranspiration Index (29°–32° N, 88°–98° E). In addition, tree-ring δ18O in Xincuo has a significant correlation with tree-ring δ18O in Bhutan. The results indicate that cellulose δ18O for A. georgei and H. tibetana in Xincuo is a good proxy for the regional hydroclimate.

This is the first time to show that alpine Cassiope fastigiata shrubs form distinct annual growth rings and record climatic signals. Cassiope species grow as dwarf shrubs at high latitudes and high elevations. Unlike in the High Arctic, not much is known about their age and growth on the Tibetan Plateau and in the Himalayas. There, Cassiope fastigiata could potentially serve as indicator species for climate change. The objective of our study, therefore, was to investigate its dendroecological potential. For this purpose, 20 shoots were collected both on the south-eastern Tibetan Plateau (site 1) and in the central Himalayas (site 2). Cross-sections of 8–10 μm in thickness were cut and the widths of the clearly distinguishable growth rings were measured. No missing outer rings were detected at the shoot base when serial sectioning was applied. Of the 40 shoots, 19 at site 1 and 10 at site 2 showed similar growth patterns. The remaining shoots were excluded from further analyses. C. fastigiata formed up to 30 annual growth rings whose width varied from 13 to 150 μm. Its growth at both sites was positively associated with temperature in late winter/early spring, and at site 2 additionally with precipitation in late autumn of the preceding year and spring of the current year. Our study confirmed that C. fastigiata forms distinct annual growth rings. The growth response to precipitation at site 1 and the lack thereof at site 2 result from differences in hydrology between the south-eastern Tibetan Plateau and the central Himalayas.

Forests around the world are subject to risk of high rates of tree growth decline and increased tree mortality from combinations of climate warming and drought, notably in semi-arid settings. Here, we assess how climate warming has affected tree growth in one of the world's most extensive zones of semi-arid forests, in Inner Asia, a region where lack of data limits our understanding of how climate change may impact forests. We show that pervasive tree growth declines since 1994 in Inner Asia have been confined to semi-arid forests, where growing season water stress has been rising due to warming-induced increases in atmospheric moisture demand. A causal link between increasing drought and declining growth at semi-arid sites is corroborated by correlation analyses comparing annual climate data to records of tree-ring widths. These ring-width records tend to be substantially more sensitive to drought variability at semi-arid sites than at semi-humid sites. Fire occurrence and insect/pathogen attacks have increased in tandem with the most recent (2007-2009) documented episode of tree mortality. If warming in Inner Asia continues, further increases in forest stress and tree mortality could be expected, potentially driving the eventual regional loss of current semi-arid forests.

Himalayan birch (Betula utilis D. Don) is a long-lived, broadleaf tree species native to the Himalayas. However, it has received limited attention for dendroclimatological studies. Based on 49 tree-ring cores from 41 Himalayan birch trees at two sites in the Langtang National Park, central Nepal, a 458-year chronology (back to AD 1552) was developed. To date, this is the longest for this species in the Himalayas despite a low sample depth before AD 1785. The chronology statistics show the potential of Himalayan birch for dendroclimatology, as indicated by a positive correlation with precipitation in May and March–May (p

Physiological and ecological mechanisms that define treelines are still debated. It is suggested that the absence of trees above the treeline is caused by the low temperature that limits growth. Thus, we raise the hypothesis that there is a critical minimum temperature (CTmin) preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir (Abies georgei var. smithii) treeline sites on the south-eastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature (CTmin) for the onset and end of xylogenesis occurred at 0.7±0.4 °C. A process-based-modeled chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.

From the viewpoints of physical geography, river and lake terraces, glacial moraines, lake sediments, ice core, stalagmite, tree-rings, loess and paleo-soils, etc. provide broad materials and contain multi-proxies to reconstruct records of environmental changes. During past 30 years, Chinese scholars have achieved many progresses, such as pollen records from lake sediments in the Tibetan Plateau and northwestern arid areas, isotope records of ice cores, climatic factors derived from tree-rings, tectonic and climatic information and their relationships based upon natural sedimentary profiles. Part of them has produced widely international effects. For deeply developing the studies of records of environmental changes, it is important to enhance regional synthesizing, quantitative reconstruction, modern processes of proxies, new technologies for sampling and analyzing.

Land surface process studies over the Tibetan Plateau had made large achievements in the last three decades, focus mainly on: (1) Multi-sphere interactions in the Tibetan Plateau and their impacts on regional climate, hydrology and ecosystem. (2) Mechanisms and impacts of cryospheric hazards, including cold regions engineering. (3) tempo-spatial patterns of paleoenvironment. Achievement was also made in the changes of polar cryosphere and their influences to high/middle latitudinal climate. Future expectation includes enhancing the modeling work on cryosphere research, multi-discipline research considering multi-sphere interaction, and the potential new directions linked to social activities.

The alpine treeline is commonly regarded as being sensitive to climatic warming because regeneration and growth of trees at treeline generally are limited by low temperature. The alpine treelines of the Tibetan Plateau (TP) occur at the highest elevations (4,900 m above sea level) in the Northern Hemisphere. Ongoing climatic warming is expected to shift treelines upward. Studies of treeline dynamics at regional and local scales, however, have yielded conflicting results, indicating either unchanging treeline elevations or upward shifts. To reconcile this conflict, we reconstructed in detail a century of treeline structure and tree recruitment at sites along a climatic gradient of 4 °C and mean annual rainfall of 650 mm on the eastern TP. Species interactions interacted with effects of warming on treeline and could outweigh them. Densification of shrubs just above treeline inhibited tree establishment, and slowed upward movement of treelines on a time scale of decades. Interspecific interactions are major processes controlling treeline dynamics that may account for the absence of an upward shift at some TP treelines despite continued climatic warming.

Seasonal asymmetry in the interannual variations in the daytime and nighttime climate in the Northern Hemisphere (NH) is well documented, but its consequences for vegetation activity remain poorly understood. Here, we investigate the interannual responses of vegetation activity to variations of seasonal mean daytime and nighttime climate in NH (>30 °N) during the past decades using remote sensing retrievals, FLUXNET and tree ring data. Despite a generally significant and positive response of vegetation activity to seasonal mean maximum temperature ("Equation missing") in ~22–25% of the boreal (>50 °N) NH between spring and autumn, spring-summer progressive water limitations appear to decouple vegetation activity from the mean summer "Equation missing", particularly in climate zones with dry summers. Drought alleviation during autumn results in vegetation recovery from the marked warming-induced drought limitations observed in spring and summer across 24–26% of the temperate NH. Vegetation activity exhibits a pervasively negative correlation with the autumn mean minimum temperature, which is in contrast to the ambiguous patterns observed in spring and summer. Our findings provide new insights into how seasonal asymmetry in the interannual variations in the mean daytime and nighttime climate interacts with water limitations to produce spatiotemporally variable responses of vegetation growth.

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.

Little is known about variations in tree phenology and their driving forces on the Tibetan Plateau. Herein, we monitored shoot growth and needle unfolding of Smith fir (Abies georgei var. smithii) between 3,800 and 4,360 m a.s.l. in the Sygera Mountains, southeastern Tibetan Plateau. The trees were 0.45–1.48 m high and 12–39 years old. Their phenology was observed every week between May 5 and August 26, 2011. With increasing elevation, shoot growth and needle unfolding started increasingly later, thus indicating a thermal driving force. Although the weekly shoot increment was decreasing with increasing elevation, height growth at various elevations ended in the same week, implying other factors than temperature being responsible for the end of height growth. The accumulated heat sum for the onset of shoot growth appeared to be lower between 4,200 and 4,360 m than between 3,800 and 4,000 m. The anticipated spring warming will likely induce an earlier onset of shoot growth, whereas shoot growth will apparently not benefit from autumn warming. However, the lack of long-term data records precluded a robust statistical test of the underlying cause-and-effect relationships involved in the phenological variations of height growth and needle unfolding.

Severe droughts were evaluated using a tree-ring network of 12 chronologies (1700−2005) from the Qilian Mountains on the northeastern Tibetan Plateau. A total of 98 drought years, including 78 moderate, 15 severe, and 5 extreme events, were identified for the past 306 yr. Following the starting year of a drought phase, drought commonly continued for 1 to 2 yr. The spatial patterns of moisture conditions in central and eastern China corresponding to 19 major drought years during the period 1700−2000 were grouped into 3 clusters, with one particular pattern showing droughts of nation-wide impact (i.e. 1721, 1928 and 1966). Drought events became more frequent during the 20th century. Moreover, the multi-year event during the late 1920s and early 1930s was the longest in the past 306 yr. As shown by the tree-ring data, this extreme drought event occurred first in the western Qilian Mountains, and then progressed gradually toward the central and eastern parts of the area, culminating in 1928. Comparison with historical documents demonstrates that the climatic information imbedded in the tree-ring network can provide quantitative measures of drought severity and fill the gaps where historical documents are lacking and/or incomplete.

Tree-ring data from timberlines have been widely used to reconstruct past temperature variability. High-quality reconstructions depend on successful calibrations in which tree-ring records are compared with instrumental observations of climatic factors to establish quantitative relationships between tree growth and climate. Climatic data used in the calibrations are mostly from nearby meteorological stations, located generally in the valleys near human settlements of mountainous areas, regardless of whether climatic records at low elevations are representative for the upper timberline. In order to better understand the characteristics of the alpine environment at the upper timberline of blackseed juniper (Juniperus saltuaria) in the eastern side of the Sygera Mountains, southeastern Tibetan Plateau, an automatic weather station was established. We found that the variation in the daily/5-day/10-day/monthly mean temperatures and sums of precipitation on the valley bottom (3000 m a.s.l.) as well as the daily/seasonal sums of precipitation from the TRMM (Tropical Rainfall Measuring Mission) are highly correlated with the measurements at the upper timberline (4400 m a.s.l.). Thus, the variations of the valley bottom temperature and precipitation records are confident indicators of the conditions at the upper timberline on the southeastern Tibetan Plateau and hence can be used for the calibration in the dendroclimatic reconstructions based on timberline tree-ring data. For 5-day mean temperature pooled by individual months, the R2 values of the regression models > 0.60 between the valley bottom and timberline in February–August and October, and 0.60 in March–July and October–December, and

Summary • As one of the world’s highest natural tree lines, the Smith fir (Abies georgei var. smithii) tree line on the southeastern Tibetan Plateau is expected to vary as a function of climate warming. However, the spatial patterns and dynamics of the Smith fir tree line are not yet well understood. • Three rectangular plots (30 m · 150 m) were established in the natural alpine tree-line ecotone on two north-facing (Plot N1, 4390 m asl; Plot N2, 4380 m asl) and one east-facing (Plot E1, 4360 m asl) slope. Dendroecological methods were used to monitor the tree-line patterns and dynamics over a 50-yr interval. • The three study plots showed a similar pattern of regeneration dynamics, characterized by increased recruitment after the 1950s and an abrupt increase in the 1970s. Smith fir recruitment was significantly positively correlated with both summer and winter temperatures. However, Smith fir tree lines do not show a significant upward movement, despite warming on the Tibetan Plateau. • The warming in the past 200 yr is already having a significant impact on the population density of the trees, but not on the position of the Smith fir tree line.

Although the southeastern Tibetan Plateau has one of the world’s highest natural treelines, little is known about its microclimatic conditions. In order to characterize microclimatic conditions for natural Blackseed juniper (Juniperus saltuaria [Rehd & Wils], syn: Sabina saltuaria )t reeline (4390 masl) in the Sygera (Sergyemla) Mountains, southeastern Tibetan Plateau, an in situ field measurement based on an automatic weather station (AWS) has been running since November 2006. The annual mean air temperature ranged from 0 to 0.8uC from 2007–2009. The mean air temperature for the warmest month (July) was 7.9 6 0.5uC, while mean air temperatures during the growing season were 6.8 6 0.3uC (Index 1) and 6.2 6 0.2uC (Index 2, corresponding to the global scale), based on a definition of the growing season according to a daily mean air temperature of .5uC and soil temperature at 10 cm depth .3.2uC. However, the mean soil temperature at a depth of 10 cm during the growing season (8.0 6 0.2uC) was higher than that measured for the global treelines. The juniper treeline is characterized by a humid microclimate, as shown by the mean daily relative humidity of 76.4%, annual total precipitation of 871.3 mm, and mean soil volumetric moisture content of 35.5% during periods when the soil is not frozen. The annual mean wind speed was 0.9 6 0.1 m/s. Uninterrupted in situ micrometeorological field measurements for alpine treelines should be the next step to achieve a better understanding of treeline ecological conditions and treeline formation on the 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. (C) 2010 Elsevier Ltd. All rights reserved.

Chir pine (Pinus roxburghii Sarg.) is a common tree species with ecological and economic importance across the subtropical forests of the central Himalayas. However, little is known about its growth response to the recent warming and drying trends observed in this region. Here, we developed a 268-year-long ring-width chronology (1743&ndash, 2010) from western Nepal to investigate its growth response to climate. Based on nearby available meteorological records, growth was positively correlated with winter (November to February, r = 0.39, p &lt, 0.05) as well as March to April (r = 0.67, p &lt, 0.001) precipitation. Growth also showed a strong positive correlation with the sum of precipitation from November of the previous year to April of the current year (r = 0.65, p &lt, 0.001). In contrast, a negative relationship with the mean temperature in March to April (r = &minus, 0.48, p &lt, 0.05) suggests the influence of warming-induced evapotranspiration on tree growth. Spring droughts lasting 4&ndash, 6 months constrain Chir pine growth. These results are supported by the synchronization between droughts and very narrow or locally missing rings. Warming and drying tendencies during winter and spring will reduce forest growth and resilience and make Chir pine forests more vulnerable and at higher risk of growth decline and dieback.