Climate Signals from Tree Ring Chronologies of the Upper and Lower Treelines in the Dulan Region of the Northeastern Qinghai-Tibetan Plateau

The radial growth of trees In mountainous areas is subject to environmental conditions associated with changes In elevation. To assess the sensitivity of tree-ring growth to climate variation over a wide range of elevations, we compared the chronological characteristics of Sabina przewalskii Kom. and their relationships with climatic variables at the upper and lower treellnes In the Dulan region of the northeastern Qlnghal-Tlbetan Plateau. It was found that the radial growth in this region was controlled primarily by precipitation in late spring and early summer （from May to June）. In addition, a higher temperature from April to June could Intensify drought stress and lead to narrow tree rings. The significant similarity In climate-tree growth relationships at both the upper and lower treellnes Indicated that tree rings of S. przewalskU In this region are able to provide common regional climate information. However, the chronologies at the lower forest limits showed a higher standard deviation and more significant correlations with climatic factors, suggesting that the radial growth there was more significantly Influenced by climate variation. The first principal component of the four chronologies showed a common growth response to local climate. The second principal component showed a contrasting growth response between different sampling sites. The third principal component revealed different growth patterns In response to altitudinal variation. Further analysis Indicated that the precipitation In late spring and early summer controlled the growth of S. przewalskii on a regional scale and that other factors, such as mlcroenvlronment at the sampling sites, also affected the strength of the climatic response of tree growth.     

Radial Growth of Qilian Juniper on the Northeast Tibetan Plateau and Potential Climate Associations

There is controversy regarding the limiting climatic factor for tree radial growth at the alpine treeline on the northeastern Tibetan Plateau. In this study, we collected 594 increment cores from 331 trees, grouped within four altitude belts spanning the range 3550 to 4020 m.a.s.l. on a single hillside. We have developed four equivalent ring-width chronologies and shown that there are no significant differences in their growth-climate responses during 1956 to 2011 or in their longer-term growth patterns during the period AD 1110–2011. The main climate influence on radial growth is shown to be precipitation variability. Missing ring analysis shows that tree radial growth at the uppermost treeline location is more sensitive to climate variation than that at other elevations, and poor tree radial growth is particularly linked to the occurrence of serious drought events. Hence water limitation, rather than temperature stress, plays the pivotal role in controlling the radial growth of Sabina przewalskii Kom. at the treeline in this region. This finding contradicts any generalisation that tree-ring chronologies from high-elevation treeline environments are mostly indicators of temperature changes.     

Drought variations in the middle Qilian Mountains,northeast Tibetan Plateau,over the last 450 years as reconstructed from tree rings

Based on the tree-ring width chronology of Sabina przewalskii Kom., a 450-year Palmer Drought Severity Index (PDSI) series was reconstructed in the middle Qilian Mountains, northeast Tibetan Plateau. During the calibration period of 1957–2004, the predictor variable accounts for 47% of the variance in the modeled PDSI data. There were three sustained severe multiyear droughts during the periods of 1705–1723, 1814–1833, and 1925–1941 before the instrumental period of 1957–2004, while no drought event lasting longer than 10 years occurred during the instrumental period. Although the modeled PDSI during the 1957–2004 period adequately assessed the intensity of the multiyear droughts for the last 450 years, the potential for prolonged droughts was underestimated. In the multidecadal scale, the drought of 1640–1730 had the greatest magnitude and the longest duration, the drought of 1808–1846 had the highest intensity, and the drought of 1917–1973 was moderate. Both the multiyear and decadal scale droughts in the middle Qilian Mountains corresponded to the droughts in the northeast Tibetan Plateau, demonstrating that drought occurrences in the northeast Tibetan Plateau are synchronous in decadal to multidecadal scales. The drought variations in the middle Qilian Mountains have significant periodicities of 2.05–2.31, 54.44, 98, and 122.5 years at a 99% confidence level.     

藏东南色季拉山急尖长苞冷杉(Abies georgei var. smithii)林线的生态气候特征

高山林线因其对气候因子的敏感性和自身结构的不稳定性而被视为气候变化的"监视器",通过自动微气象站对藏东南色季拉山急尖长苞冷杉(Abies georgei var. smithii)林线气象因子的连续监测,探讨了色季拉山高山林线的生态气候特征.结果表明:在色季拉山急尖长苞冷杉林线处,年平均温度为1.3℃,年平均相对湿度为79.4%,全年降水量为892.6 mm,主要集中在6、7、8、9月4个月份.林线最热月平均温度为9.4℃,最冷月平均温度为-6.4℃,年生物温度为3.1℃,温暖指数是11.6℃月,寒冷指数是-55.9℃月,生长季内平均温度为7.7℃,生长季长度为133d,大陆度指数为34.0,湿润指数为217.5.其温暖指数与我国两种山地森林树种祁连圆柏和喜马拉雅冷杉的分布上限较为接近.林线的最热月温度、年生物学温度和生长季平均温度与全国高山林线的平均值十分接近.从全球范围来看,色季拉山林线最热月平均温度9.4℃与全球均值10℃很接近.生长季内10cm深度的土壤均温为6.22℃,接近Krner观测的(6.7±0.8)℃全球均值.     

Growth variation in Abies georgei var. smithii along altitudinal gradients in the Sygera Mountains, southeastern Tibetan Plateau

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

Disentangling the Legacies of Climate and Management on Tree Growth

Ecosystems - Legacies of past climate conditions and historical management govern forest productivity and tree growth. Understanding how these processes interact and the timescales over which they...     

A modern pollen–climate calibration set based on lake sediments from the Tibetan Plateau and its application to a Late Quaternary pollen record from the Qilian Mountains

Aim Fossil pollen spectra from lake sediments on the Tibetan Plateau have been used for qualitative climate reconstruction, but no modern pollen–climate calibration set based on lake sediments is available to infer past climate quantitatively. This study aims to develop such a dataset and apply it to fossil data. Location The Tibetan Plateau, between 30 and 40° N and 87 and 103° E. Methods We collected surface sediments from 112 lakes and analysed them palynologically. The lakes span a wide range of mean annual precipitation (P_ann; 31–1022 mm), mean annual temperature (T_ann; −6.5 to 1 °C), and mean July temperature (T_July; 2.6–19.7 °C). Redundancy analysis showed that the modern pollen spectra are characteristic of their respective vegetation types and local climate. Transfer functions for P_ann, T_ann and T_July were developed with weighted averaging partial least squares. Model performance was assessed by leave-one-out cross-validation. Results The root mean square errors of prediction (RMSEP) were 104 mm (P_ann), 1.18 °C (T_ann) and 1.17 °C (T_July). The RMSEPs, when expressed as percentages of the gradient sampled, were 10.6% (P_ann), 15.7% (T_ann) and 11.9% (T_July). These low values indicate the good performance of our models. An application of the models to fossil pollen spectra covering the last c. 50 kyr yielded realistic results for Luanhaizi Lake in the Qilian Mountains on the north-eastern Tibetan Plateau (modern P_ann 480 mm; T_ann−1 °C). T_ann and P_ann values similar to present ones were reconstructed for late Marine Isotope Stage 3, with minimum values for the Last Glacial Maximum (c. 300 mm and 2 °C below present), and maximum values for the early Holocene (c. 70 mm and 0.5 °C greater than present). Main conclusions The modern pollen–climate calibration set will potentially be useful for quantitative climate reconstructions from lake-sediment pollen spectra from the Tibetan Plateau, an area of considerable climatic and biogeographical importance.     

Tree growth responses and resilience after the 1950-Zayu-Medog earthquake,southeast Tibetan Plateau

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 M_W 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.     

Group size effect on vigilance: evidence from Tibetan gazelle in Upper Buha River, Qinghai-Tibet Plateau

Tibetan gazelle Procapra picticaudata is a threatened and endemic species to the Qinghai-Tibet Plateau. With the method of group scan sampling, we observed the behaviours of males and females of the gazelle in the two summers of 2005 and 2006, in order to test the group size effect on group vigilance. We found that male gazelles were significantly more vigilant than the females at both group scan level (percentage of individuals scanning during a session) and group scan frequency (percentage of intervals with at least one individual scanning). We also found a negative correlation between group scan level and group size and a positive correlation between group scan frequency and group size, showing the group size effect on vigilance was testified in Tibetan gazelle. The predation factor might be the main driving force for the group size effect.     

Dynamic relationships between Picea crassifolia growth and climate at upper treeline in the Qilian Mts., Northeast Tibetan Plateau, China

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

Growth Rings,Phenology, Hurricane Disturbance and Climate in Cyrilla racemiflora L., a Rain Forest Tree of the Luquillo Mountains,Puerto Rico1

The growth phenology of Cyrilla racemiflora L., the dominant tree species of the montane rain forest, (subtropical lower montane rain forest, sensu Holdridge) of the Luquillo Mountains of Puerto Rico was studied intensively during 1989, and then semiannually through mid-1993 to determine the periodicity of changes in xylem structure. Four trees at 770 m were monitored for flowering, branch elongation, leaf litterfall, and xylem cell growth and differentiation in the lower stem, and these events were related to local seasonal patterns of rainfall and temperature. Hurricane Hugo defoliated study trees in September, 1989. Bud-break and branch elongation in March, 1989 were followed by earlywood xylem cell production in the lower stem in April and the onset of flowering in May. Leaf litterfall was greatest between April and June, coinciding with peak branch growth and new leaf formation. Latewood xylem was produced in December. The general phenological pattern was synchronized between trees and over study years. Vessel diameter and density were monitored along with thickness of earlywood and latewood and the former converted to vessel lumen area, a measure of xylem conductance capacity. Annual growth rings were formed with periods of earlywood and latewood production coinciding with traditional summer (rainy) and winter (dry) seasons, respectively, in the Luquillo Mountains. Hurricane defoliation was followed by heavy flowering in 1990, a year of reduced branch elongation and annual xylem ring width, and was associated with maximum vessel lumen area, as was flowering in 1989, prior to the hurricane. Hurricane Hugo provided a perturbation that, through its elicited stress response, allowed for the demonstration of the interplay between flowering, branching, structural growth of xylem, and xylem function.     

Summer temperature variability inferred from tree-ring records in the central Hengduan Mountains,southeastern Tibetan Plateau

Current understanding of the paleoclimatic variability across the Tibetan Plateau (TP) is still limited because of the lack of long-term climatic records. We developed a regional tree–ring width chronology of Picea likiangensis var. balfouriana from the central Hengduan Mountains region, in the southeastern TP. Climate-growth correlation analysis revealed that the current year’s July (cJuly) and the current year’s August (cAugust) mean minimum temperature was the main climatic factor controlling tree-ring growth. Using a linear regression function, we reconstructed this indicator for the past 214 years (1795–2008) to produce the first mean minimum temperature reconstruction for the central Hengduan Mountains. The reconstruction satisfied all statistical calibration and validation tests, and represented 35.9% of the temperature variance recorded over the 1958–2008 instrumental period (34.6% after adjusting for the loss of the degrees of freedom). During the past 214 years, two major cold periods were identified from 1839 to 1853 and 1857–1942, and four major warm periods from 1802 to 1813, 1819–1838, 1972–1981, and 1988–2008. The degree of warming from 1988 to 2008 was unprecedented over the past two centuries. Spatial field correlation with the gridded temperature dataset revealed that our reconstruction captures large-scale regional temperature variations for the southeastern TP and its vicinity. The reconstructed variations were consistent when compared to other regional temperature datasets, historical documents, and records of glacier fluctuations in the surrounding high mountains. This consistency with multiple records suggests that our reconstructed sequence is reliable and it could represent historical large-scale temperature changes on the southeastern TP.     

Variation of maximum tree height and annual shoot growth of Smith fir at various elevations in the Sygera Mountains, southeastern Tibetan Plateau

Little is known about tree height and height growth (as annual shoot elongation of the apical part of vertical stems) of coniferous trees growing at various altitudes on the Tibetan Plateau, which provides a high-elevation natural platform for assessing tree growth performance in relation to future climate change. We here investigated the variation of maximum tree height and annual height increment of Smith fir (Abies georgei var. smithii) in seven forest plots (30 m×40 m) along two altitudinal transects between 3,800 m and 4,200/4,390 m above sea level (a.s.l.) in the Sygera Mountains, southeastern Tibetan Plateau. Four plots were located on north-facing slopes and three plots on southeast-facing slopes. At each site, annual shoot growth was obtained by measuring the distance between successive terminal bud scars along the main stem of 25 trees that were between 2 and 4 m high. Maximum/mean tree height and mean annual height increment of Smith fir decreased with increasing altitude up to the tree line, indicative of a stress gradient (the dominant temperature gradient) along the altitudinal transect. Above-average mean minimum summer (particularly July) temperatures affected height increment positively, whereas precipitation had no significant effect on shoot growth. The time series of annual height increments of Smith fir can be used for the reconstruction of past climate on the southeastern Tibetan Plateau. In addition, it can be expected that the rising summer temperatures observed in the recent past and anticipated for the future will enhance Smith fir's growth throughout its altitudinal distribution range.     

Tree growth and climate sensitivity in open and closed forests of the southeastern Tibetan Plateau

The creation of forest openings is a frequently observed phenomenon in many types of forests. On the southeastern Tibetan Plateau, where the average elevation is greater than 4000 m above sea level, differences in tree growth between forest stands with openings and completely closed stands are poorly characterized. Here, we presented a dendrochronological study of Tibetan juniper (Juniperus tibetica Kom.) and Sikkim spruce (Picea spinulosa (Griff.) Beissn.) in an open and a closed stand, near Qamdo of eastern Tibet. We found that the growth of juniper responded to climate in a similar way in the open and closed stands, and was positively correlated with temperature from October to January and with the Palmer Drought Severity Index (PDSI) from September to June. In contrast, the growth of spruce responded to climate differently in the open and closed stands: growth was positively correlated with the PDSI from September to May in the open stand, whereas it was positively correlated to November and December temperatures (of the prior year) and current June temperature in the closed stand. Interannual variation in, and standard deviations among, juniper tree ring widths were similar in both stands for the past four centuries, whereas they differed in spruce over the past two centuries, particularly in the 1900s. These results suggest that juniper tree ring growth is less sensitive to stand structure than that of spruce, thus providing more reliable climate signals. The data obtained from our study will help forest managers understand the ecology of juniper and spruce in open and closed stands and are therefore useful for management planning.     

三参数增长模型拟合:以季风常绿阔叶林中两个优势乔木种群为例

Logistic、Mitscherlich、Gompertz方程是一类三参数饱和增长曲线模型,广泛地应用于许多学科领域．本文基于logistic方程饱和值K估计的三点法、四点法,推导出Mitscherlich、Gompertz方程K值的三点法、四点法估计公式,并以南亚热带季风常绿阔叶林中两种优势乔木厚壳桂、黄果厚壳桂种群为例,先用三点法或四点法估计出K值,再通过线性回归与非线性回归相结合的方法,可获得三个增长模型中三个参数的最优无偏估计．实例研究表明,两个优势种群增长数据均符合三个增长模型,但更符合增长曲线呈S形的logistic、Gompertz方程,且以logistic方程最适合于观察;黄果厚壳桂种群增长快于厚壳桂种群．     

Leaf traits and associated ecosystem characteristics across subtropical and timberline forests in the Gongga Mountains,Eastern Tibetan Plateau

Knowledge of how leaf characteristics might be used to deduce information on ecosystem functioning and how this scaling task could be done is limited. In this study, we present field data for leaf lifespan, specific leaf area (SLA) and mass and area-based leaf nitrogen concentrations (N_mass, N_area) of dominant tree species and the associated stand foliage N-pool, leaf area index (LAI), root biomass, aboveground biomass, net primary productivity (NPP) and soil available-N content in six undisturbed forest plots along subtropical to timberline gradients on the eastern slope of the Gongga Mountains. We developed a methodology to calculate the whole-canopy mean leaf traits to include all tree species (groups) in each of the six plots through a series of weighted averages scaled up from leaf-level measurements. These defined whole-canopy mean leaf traits were equivalent to the traits of a leaf in regard to their interrelationships and altitudinal trends, but were more useful for large-scale pattern analysis of ecosystem structure and function. The whole-canopy mean leaf lifespan and leaf N_mass mainly showed significant relationships with stand foliage N-pool, NPP, LAI and root biomass. In general, as elevation increased, the whole-canopy mean leaf lifespan and leaf N_area and stand LAI and foliage N-pool increased to their maximum, whereas the whole-canopy mean SLA and leaf N_mass and stand NPP and root biomass decreased from their maximum. The whole-canopy mean leaf lifespan and stand foliage N-pool both converged towards threshold-like logistic relationships with annual mean temperature and soil available-N variables. Our results are further supported by additional literature data in the Americas and eastern China.     

祁连山冷龙岭南麓垂直带植被移地试验中鹅绒委陵菜克隆生长特征

在祁连山东段冷龙岭南麓海拔3 200～3 800 m的4个样地间按主要植被类型进行双向移地试验,以自然垂直带移地样方内鹅绒委陵菜(Potentilla anserina)为研究对象,调查其克隆生长对气候变化的响应和适应特征.结果表明:鹅绒委陵菜从海拔3 200 m和3 400 m分别双向移至4个不同海拔区生长1年后,所有样地中1条匍匐茎的植株最多(占43.66%),4条匍匐茎的最少(占4.23%);随海拔升高,它们的匍匐茎总条数分别表现为逐渐增多和减少-增加-减少的趋势,基株高度和基叶数均呈先增加后减少的显著变化趋势,分株数逐渐增加,间隔子长度分别呈先增加后减少和增加-减小-增加的趋势;匍匐茎长度在移到3 400 m时最大,移到3 800 m时最小.研究发现,移地后鹅绒委陵菜的匍匐茎数、基株高度、基叶数、分株数、间隔子长度等均可发生变化;鹅绒委陵菜对不同海拔高度的生态环境表现出不同的克隆生长特征,以适应环境稳定种群.     

Projections of Water Stress Based on an Ensemble of Socioeconomic Growth and Climate Change Scenarios: A Case Study in Asia

The sustainability of future water resources is of paramount importance and is affected by many factors, including population, wealth and climate. Inherent in current methods to estimate these factors in the future is the uncertainty of their prediction. In this study, we integrate a large ensemble of scenarios—internally consistent across economics, emissions, climate, and population—to develop a risk portfolio of water stress over a large portion of Asia that includes China, India, and Mainland Southeast Asia in a future with unconstrained emissions. We isolate the effects of socioeconomic growth from the effects of climate change in order to identify the primary drivers of stress on water resources. We find that water needs related to socioeconomic changes, which are currently small, are likely to increase considerably in the future, often overshadowing the effect of climate change on levels of water stress. As a result, there is a high risk of severe water stress in densely populated watersheds by 2050, compared to recent history. There is strong evidence to suggest that, in the absence of autonomous adaptation or societal response, a much larger portion of the region’s population will live in water-stressed regions in the near future. Tools and studies such as these can effectively investigate large-scale system sensitivities and can be useful in engaging and informing decision makers.     

青藏高原高寒草甸生态系统高原鼠兔种群调查及其防控阈值研究（英文）

认识高原鼠兔Ochotona curzoniae在草地退化中的角色和地位,对于加强高寒草甸生态系统高原鼠兔种群管理具有重要的意义。以高原鼠兔有效洞穴密度为调查对象,根据所调查的12个样地遴选出4个不同鼠洞等级的研究样地去评估鼠兔数量和植物生物量变化之间的关系。主要结论如下:高原鼠兔活动并非引起草地退化的原因,而是作为草地退化的标志性信号,然而高频度的鼠兔活动会加剧草地逆向演替的进程。因此,一些综合措施诸如减少牲畜数量、动态的轮牧、草地恢复管理技术、社区参与式管理等可以有效提高草地生产力和防止鼠害爆发。对各类型退化草地进行综合治理时,应加强对害鼠种群动态的监测,当种群密度超过经济阈值或达到高密度种群时,应急性、常规性灭鼠工作才可以实施,为重度型退化草地重建、植被恢复和土壤发育提供可能性。