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.     

Difference in tree growth responses to climate at the upper treeline: Qilian Juniper in the Anyemaqen Mountains

Three ring-width chronologies were developed from Qilian Juniper (Sabina przewalskii Kom.) at the upper treeline along a west-east gradient in the Anyemaqen Mountains.Most chronological statistics,except for mean sensitivity (MS),decreased from west to east.The first principal component (PC1) Ioadings indicated that stands in a similar climate condition were most important to the variability of radial growth.PC2 Ioadings decreased from west to east,suggesting the difference of tree-growth between eastern and western Anyemaqen Mountains.Correlations between standard chronologies and climatic factors revealed different climatic influences on radial growth along a west-east gradient in the study area.Temperature of warm season (July-August) was important to the radial growth at the upper treeline in the whole study area.Precipitation of current May was an important limiting factor of tree growth only in the western (drier) upper treeline,whereas precipitation of current September limited tree growth in the eastern (wetter) upper treeline.Response function analysis results showed that there were regional differences between tree growth and climatic factors in various sampling sites of the whole study area.Temperature and precipitation were the important factors influencing tree growth in western (drier) upper treeline.However,tree growth was greatly limited by temperature at the upper treeline in the middle area,and was more limited by precipitation than temperature in the eastern (wetter) upper treeline.     

Treeline dynamics in relation to climatic variability in the central Tianshan Mountains, northwestern China

Aim Climate variability may be an important mediating agent of ecosystem dynamics in cold, arid regions such as the central Tianshan Mountains, north‐western China. Tree‐ring chronologies and the age structure of a Schrenk spruce (Picea schrenkiana) forest were developed to examine treeline dynamics in recent decades in relation to climatic variability. Of particular interest was whether tree‐ring growth and population recruitment patterns responded similarly to climate warming. Location The study was conducted in eight stands that ranged from 2500 m to 2750 m a.s.l. near the treeline in the Tianchi Nature Reserve (43°45′?43°59′ N, 88°00′?88°20′ E) in the central Xinjiang Uygur Autonomous Region, northwestern China. Methods Tree‐ring cores were collected and used to develop tree‐ring chronologies. The age of sampled trees was determined from basal cores sampled as close as possible to the ground. Population age structure and recruitment information were obtained using an age–d.b.h. (diameter at breast height) regression from the sampled cores and the d.b.h. measured on all trees in the plots. Ring‐width chronologies and tree age structure were both used to investigate the relationship between treeline dynamics and climate change. Results Comparisons with the climatic records showed that both the radial growth of trees and tree recruitment were influenced positively by temperature and precipitation in the cold high treeline zone, but the patterns of their responses differed. The annual variation in tree rings could be explained largely by the average monthly minimum temperatures during February and August of the current year and by the monthly precipitation of the previous August and January, which had a significant and positive effect on tree radial growth. P. schrenkiana recruitment was influenced mainly by consecutive years of high minimum summer temperatures and high precipitation during spring. Over the last several decades, the treeline did not show an obvious upward shift and new recruitment was rare. Some trees had established at the treeline at least 200 years ago. Recruitment increased until the early 20th century (1910s) but then decreased with poor recruitment over the past several decades (1950–2000). Main conclusions There were strong associations between climatic change and ring‐width patterns, and with recruitments in Schrenk spruce. Average minimum temperatures in February and August, and total precipitation in the previous August and January, had a positive effect on tree‐ring width, and several consecutive years of high minimum summer temperature and spring precipitation was a main factor favouring the establishment of P. schrenkiana following germination within the treeline ecotone. Both dendroclimatology and recruitment analysis were useful and compatible to understand and reconstruct treeline dynamics in the central Tianshan Mountains.     

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.     

天山东部西伯利亚落叶松树轮生长对气候要素的响应分析

天山东部西伯利亚落叶松的树木年轮学研究可以看出：森林上限树轮宽度年表之间相关性较高而下限年表间相关稍低,表明下限小生境要素对树木生长干扰较大。森林上下限树轮年表中样本的总解释量（ESP）和信噪比（SNR）都比较高,说明树木中都含有较多的环境信息;但标准年表中平均敏感度（M．S．）和轮宽指数的标准差（S．D．）都是森林上限数值低于下限,这表明森林上限树木生长对环境变化响应的敏感性降低;相关分析和响应分析也发现森林下限生长的树木对气候因子的响应较为显著。就温度而言,森林上限和下限表现基本一致,树木生长多与温度负相关,其中下限树木生长与春季均温和3．6月份均温显著负相关;降水表现出一定的差别,上限树木生长与春季、夏季及年降水量有较高的负相关,而对下限树木生长影响最大的则是冬季和3—6月份降水。湿润指数与降水基本一致即上限呈负相关而下限正相关,温暖指数全为负相关,寒冷指数下限负相关显著;显然该地区森林上下限树木生长的生态模式存在着一定的差异。研究发现,冬春季节的不同水热组合则是形成树木年轮宽窄的限制因素;同时,前期生长的滞后效应对年轮形成有重要的影响。     

Growth patterns of <Emphasis Type="Italic">Nothofagus pumilio</Emphasis> trees along altitudinal gradients in Tierra del Fuego,Argentina

The influence of ecological factors resulting from altitude on growth characteristics of Nothofagus pumilio was analyzed. N. pumilio forests grow in the southern Andes from near sea level to 600 m.a.s.l. Eight study sites were selected in the southwestern area of Tierra del Fuego, on north- and south-facing slopes, and distributed along an altitudinal gradient (200–600 m.a.s.l.). Growth cycles throughout time were identified. The correlation between climate and tree growth was determined. Tree diameter and height decreased whereas stand density increased towards tree-line. South-facing slopes showed higher values in common growth variability, probably because of stronger climatic controlling factors. Climate-growth correlation models revealed long-term temperature influences on growth variability, and showed variations among the different plots. Differences were detected in the spectral power component of the chronologies throughout the altitudinal profile. The series had a significant spectral peak at frequencies around 7 years, possibly related to mast seeding cycles. This signal became weaker as the altitude increased probably due to lower seed production. These results suggest a strong altitudinal component in growth variability of N. pumilio in Tierra del Fuego.     

祁连山中部地区树轮宽度年表特征随海拔高度的变化

利用采自祁连山中部地区不同海拔高度的四个采样点的青海云杉树轮样芯 ,分别建立了树木年轮宽度年表。发现随海拔高度的上升 ,树轮宽度指数的振幅减小 ,年表的平均敏感性降低 ,样本间的一致性也逐步减小 ,上限年表与气候因子的相关性最低 ,这与目前大家普遍认同的上限树木的生长受温度控制的概念并不一致。进一步的分析表明 ,年表的敏感性随海拔高度降低主要是由于该区域树木生长的限制因子是春季降水 ,而降水随海拔高度的升高而增加 ,从而使得春季降水对树木生长的限制作用随海拔升高而逐步减弱 ;生物学指标的测定结果表明 ,生长在高海拔的树木对环境的生态适应策略发生变化 ,其生理代谢维持在较低水平 ,以避免环境变化带来的影响 ,因此生长在高海拔的青海云杉对环境变化的敏感性较差。     

Interannual growth response of Norway spruce to climate along an altitudinal gradient in the Tatra Mountains, Poland

Ring-width chronologies of Picea abies (L.) Karst. from ten sites in the Tatra Mountains, Poland, were developed to explore growth/climate responses in stands along an altitudinal gradient ranging from 839 to 1468 m a.s.l. There were positive relationships between current-year radial growth and mean monthly temperatures in March, April, June and July, but with increasing elevation, the strength of this correlation declined for March–April and increased for June–July temperatures. The mean monthly temperature in October of the previous year positively influenced radial growth of trees at all sites. Lower mean temperatures in January negatively affected growth of trees at the high-elevation sites. Trees at the low-elevation sites responded positively to a warm early spring, whereas trees at the high-elevation sites showed positive growth responses to higher summer temperatures. Growth of trees at the high-elevation sites was better explained by the temperature regime than was growth at the lower-elevation sites. Therefore, it is likely that these sites may be particularly sensitive to potential effects of temperature change.     

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.     

坡向对海拔梯度上祁连圆柏树木生长的影响

选择青海省同德县南部河北林场的一个连续坡面,根据不同海拔和坡向设置4个采样点,采集祁连圆柏(Sabina przewalskii)树轮数据,分析不同海拔和坡向对树木生长的影响。结果表明:坡面上部3个采样点的树轮年表特征值均呈一定的变化规律——平均敏感值(MS)和标准差(SD)随海拔升高而增大,一阶自相关(AC)随海拔升高而递减,下限年表特征值均表现出与其他3点的不同,都是最值(MS和SD均最大,AC最小);年表间相关和主成分分析结果都显示出海拔梯度上的变化规律,但下限差异显著;树轮指数与当年6–8月平均气温的相关系数呈增强趋势,森林上限受当年7、8月平均气温影响较大,下限树轮指数不仅与当年6月和前一年11月的气温显著负相关,而且受前一年8月和当年5月的月降水量影响显著。与通常情况"下限树木生长受降水制约"比较,这里的温度作用增强而降水限制减弱。显然,坡向扭转是海拔梯度上影响祁连圆柏生长变化的重要因子。     

Temporal dynamic of wood formation in Pinus cembra along the alpine treeline ecotone and the effect of climate variables

We determined the temporal dynamic of cambial activity and xylem development of stone pine (Pinus cembra L.) throughout the treeline ecotone. Repeated micro-sampling of the developing tree ring was carried out during the growing seasons 2006 and 2007 at the timberline (1,950 m a.s.l.), treeline (2,110 m a.s.l.) and within the krummholz belt (2,180 m a.s.l.) and the influence of climate variables on intra-annual wood formation was determined. At the beginning of both growing seasons, highest numbers of cambial and enlarging cells were observed at the treeline. Soil temperatures at time of initiation of cambial activity were c. 1.5°C higher at treeline (open canopy) compared to timberline (closed canopy), suggesting that a threshold root-zone temperature is involved in triggering onset of above ground stem growth. The rate of xylem cell production determined in two weekly intervals during June through August 2006–2007 was significantly correlated with air temperature (temperature sums expressed as degree-days and mean daily maximum temperature) at the timberline only. Lack of significant relationships between tracheid production and temperature variables at the treeline and within the krummholz belt support past dendroclimatological studies that more extreme environmental conditions (e.g., wind exposure, frost desiccation, late frost) increasingly control tree growth above timberline. Results of this study revealed that spatial and temporal (i.e., year-to-year) variability in timing and dynamic of wood formation of P. cembra is strongly influenced by local site factors within the treeline ecotone and the dynamics of seasonal temperature variation, respectively.     

Climate response of Picea schrenkiana based on tree-ring width and maximum density

The effect of global warming on alpine forests is complex. It is crucial, therefore, to investigate the effects of climate change on the radial growth of trees at different altitudes. The tree growth–climate relationship remains poorly understood at large spatial scales in the Tianshan Mountains, China. Schrenk spruce (P. schrenkiana) is a unique tree species to this area. In this study, we collected tree-ring width and maximum density data from nine plots along an altitudinal gradient. Results showed that altitude affected both tree-ring width and maximum density. At high altitudes, tree-ring width was positively correlated with temperature in February of the current year. Tree-ring width was also positively correlated with precipitation in July of the previous year, and January and July of the current year, and negatively correlated with the monthly diurnal temperature range (DTR). At low altitudes, tree-ring width was negatively correlated with temperature in the early growing season and the growing season. Tree-ring width was positively correlated with precipitation in June and September of the previous year, and May of the current year. The tree-ring maximum density was positively correlated with temperature and the DTR of the growing season, and negatively correlated with precipitation in winter and growing season. Moving correlation analysis showed that the positive response of tree-ring width to precipitation in the growing season was enhanced over time at high altitudes. In the low-altitude trees, the negative response of tree-ring width to temperature in the growing season was reduced, while the positive response to precipitation in the growing season was enhanced. The positive response relationship between tree-ring maximum density and the temperature in July weakened over time. At low altitudes, the negative response of tree-ring maximum density to winter precipitation was strengthened, and a stable negative response to July precipitation was observed. As the climate becomes wetter and warmer in the Tianshan Mountains, our results suggest that the radial growth of trees may benefit at elevations above 2400 m a.s.l. There was no obvious elevation limit for the increase in tree-ring maximum density. These findings provide a basis for sustainable forest management under global climate change.     

阿尼玛卿山地不同海拔青海云杉(Picea crassifolia)树轮生长特性及其对气候的响应

利用位于同一坡面的青海云杉树芯样本,建立了4个海拔高度的树轮宽度指数年表。分析结果表明年表序列特征值大都因海拔而不同,各年表序列对气候因子的相关性在不同高度也表现出一定的差异:树木生长都与前一年10月份月均温显著正相关,与前一年8月份和当年5、6月份月均温显著负相关;与前一年9、10月份和当年5月份的降水量都呈显著正相关,但都随海拔升高呈波状变化。树轮宽度指数与不同时段的温度和温暖指数都呈负相关,表明5～9月是该地区青海云杉生长较为活跃的季节。响应函数分析结果表明该地区低海拔生长的青海云杉受温度和降水的影响都比高海拔生长的更显著,显然不同于以前研究的森林上下限树木的生长模式。4a表主成分中的第一主分量贡献率为81.071%,表明同一坡面影响树木生长的大环境因子是一致的。第一主分量与气候因子的相关分析同样显示出前一年生长季末和当年生长季初的水热组合是树木生长的主要限制因子,区域模拟也进一步证明了这一点。并认清了同一坡面青海云杉树轮记录的共性和差异,为今后树轮采样和研究提供一定的理论依据。     

芦芽山阳坡不同海拔华北落叶松径向生长对气候变化的响应

为研究树木生长对气候变化的响应状况,选取芦芽山阳坡的3个海拔高度建立了华北落叶松(Larix principis-rupprechtii)的树轮宽度年表。年表的统计参数表明,3条年表均为研究气候信息的可靠资料。结果表明,芦芽山阳坡华北落叶松的径向生长和生长与气候的关系均具有海拔差异,中海拔(2440 m)和高海拔(2540 m)的华北落叶松具有相似年际生长变化,而二者均与低海拔(2330 m)华北落叶松的年际生长不同。低海拔华北落叶松的生长与4月平均气温和上一年11月降水量显著负相关,而中海拔和高海拔的生长均与上一年10月平均气温和6月降水量显著负相关。通过年表与气候因子之间的滑动相关分析发现,3个海拔高度华北落叶松生长与气候因子的关系均不稳定,生长与气温条件之间的显著相关关系是随着气温升高而出现的。气温的升高引起了华北落叶松生长与气温因子关系的海拔差异,以及径向生长的海拔差异。这一结果对于气候变化对植被垂直梯度影响的研究具有一定参考价值。     

Climatic responses of Pinus pseudostrobus and Abies religiosa in the Monarch Butterfly Biosphere Reserve,Central Mexico

Understanding the effects of climate on the growth of trees is important to project the response of forests to climate change. Dendrochronological analysis offers a “proxy” source for the effects of climatic variation on tree growth at different spatial and temporal scales. To examine influences of temperature and precipitation on radial growth of Pinus pseudostrobus and Abies religiosa, this study combines measurements of radial growth patterns of forest trees in the Monarch Butterfly Biosphere Reserve (MBBR) in central Mexico with temperature and precipitation variables from instrumental records. Dendrochronological samples were collected as cross sections and increment cores by using a chainsaw and increment borers, respectively. Total ring-width chronologies were developed for each site. Principal component analyses (PCA) were used to identify common temperature, precipitation and tree growth variation patterns. Correlation and response function analyses between chronologies and records of temperature and precipitation were used to evaluate the relation of climate variables on tree growth. The months during which tree growth was most strongly affected by precipitation were January, February and October from the previous year; only the temperature of September from the previous year affected the tree growth. In some chronologies, May’s average monthly maximum temperature was negatively correlated with tree growth. PCA and a comparison of PCA factor scores of climatic variables and chronologies showed no significant differences between northern, central or southern portions of the MBBR. Apparently, tree growth in the MBBR is reduced in years of low January–May precipitation combined with high summer (September of the previous year) temperatures, a scenario which is likely to occur as a consequence of global climate change.     

Long-term changes in tree-ring–climate relationships at Mt. Patscherkofel (Tyrol,Austria) since the mid-1980s

Although growth limitation of trees at Alpine and high-latitude timberlines by prevailing summer temperature is well established, the loss of thermal response of radial tree growth during last decades has repeatedly been addressed. We examined long-term variability of climate–growth relationships in ring width chronologies of Stone pine (Pinus cembra L.) by means of moving response functions (MRF). The study area is situated in the timberline ecotone (ca. 2,000–2,200 m a.s.l.) on Mt. Patscherkofel (Tyrol, Austria). Five site chronologies were developed within the ecotone with constant sample depth (≥19 trees) throughout most of the time period analysed. MRF calculated for the period 1866–1999 and 1901–1999 for ca. 200- and ca. 100-year-old stands, respectively, revealed that mean July temperature is the major and long-term stable driving force of Pinus cembra radial growth within the timberline ecotone. However, since the mid-1980s, radial growth in timberline and tree line chronologies strikingly diverges from the July temperature trend. This is probably a result of extreme climate events (e.g. low winter precipitation, late frost) and/or increasing drought stress on cambial activity. The latter assumption is supported by a <10% increase in annual increments of ca. 50-year-old trees at the timberline and at the tree line in 2003 compared with 2002, when extraordinary hot and dry conditions prevailed during summer. Furthermore, especially during the second half of the twentieth century, influence of climate variables on radial growth show abrupt fluctuations, which might also be a consequence of climate warming on tree physiology.     

Vegetation structure along the altitudinal gradient at the treeline of Mount Paektu,North Korea

Vegetation structure of the treeline was studied on the southeastern slope of Mount Paektu (North Korea). Fifteen temporary plots (20m×20m) were situated along the altitudinal transect. Seven square samples (phytosociological relevés 5 m×5 m) were analyzed in each plot. Although the character of the vegetation was rather continuous altitudinally, five similar groups of vegetation samples were distinguished by the TWINSPAN procedure. The distribution of samples in the classification showed not only the effect of altitude but also the effect of competition between the tree and the shrub layers and other factors. In the canonical correspondence analysis (CCA) ordination several environmental variables were used (such as altitude of each plot, distance of each plot from the forest edge and the cover percentage of tree, shrub, herb and moss/lichen layers). The variable ‘cover of tree layer’ had the strongest relation to the species data. Continuous changes of species richness along the altitude were confirmed. Species richness decreased significantly with altitude.     

Growth responses to climate in a tree-ring network of European beech (Fagus sylvatica L.) from the eastern limit of its natural distribution area

The first dendrochronological network of European beech (Fagus sylvatica L.) from eastern limit of its distribution was established covering the species’ altitudinal range (210–1160 m a.s.l.) and three eco-regions. Statistical analysis revealed spatial trends among the 14 chronologies, with increasing tree-ring variability and synchronicity towards the east, particularly expressed by rBAR (mean interseries correlation). By means of HCA (Hierarchical Cluster Analysis) and PCA (Principal Component Analysis), the chronologies were divided into three main groups: a Mountain, Plateau and Eastern class. These correspond to the Alpine South, Continental and Pannonian bioclimatological zones. Dendroclimatological analysis revealed a general climate response pattern, with summer temperatures, April–May precipitation and April–June drought being the main limiting factors in the study area. The intensity of the correlations increases towards the eastern distribution limits and decreases towards the upper treeline of European beech. Similarly, the length of the climate-sensitive period changes, with the precipitation window increasing from April in the Mountains region to March–May in the East region and the scPDSI (self-calibrated Palmer drought severity index) window increasing from April–June in the Mountains to the previous July to the current September in the East. The western and uppermost site shows signs of being limited by low July temperatures. This chronology network represents a sensitive monitoring instrument to quantify the impact and adaptability of European beech to actual and future climatic change.     

不同海拔温度和降水对新疆阿尔泰山西伯利亚落叶松径向生长的影响

为定量并分离关键气候因子对新疆阿尔泰山不同海拔树木径向生长的影响,通过对高、中和低海拔的西伯利亚落叶松(Larixsibirica)树轮宽度标准年表与气候因子分别进行相关、多元线性回归等统计分析,并进一步计算了线性模型中不同气候因素的绝对和相对贡献率。结果表明,高海拔地区,当年6月温度和上年7月降水分别与径向生长呈显著正相关和负相关,两者共同解释西伯利亚落叶松径向生长变异的33.1%,相对贡献率分别为66.2%和33.8%;中海拔地区,当年6月温度和上年6月降水分别与径向生长呈显著正相关和负相关,两者共同解释径向生长变异的26.8%,相对贡献率分别为40.1%和59.9%;低海拔地区,上年6月温度和7月降水分别与径向生长呈显著负相关和正相关,两者共同解释径向生长变异的29.4%,相对贡献率分别为31.9%和68.1%。这表明限制树木径向生长的主要影响因子随海拔的不同而异,在高海拔地区,温度是主要限制因子;而在低海拔地区,降雨是主要限制因子。     

Age-dependent tree-ring growth responses to climate in Qilian juniper (Sabina przewalskii Kom.)

Qilian juniper (Sabina przewalskii kom.) is one of the dominant tree species on Qinghai-Tibetan Plateau and has been used in dendroclimatological studies. Here we designed a test to examine whether or not the climate–growth responses in tree rings of Qilian Juniper vary with the change in tree's age. A total number of 135 increment cores were sampled from Qilian Juniper trees at five sites, in which 112 cores were selected and grouped into five 100-year age classes for analysis of age-dependent climate–growth relationships. Chronology statistics, response functions and ANOVA F-test were used to test the consistency of five age-class mean chronologies (AGCs). The results showed that mean sensitivity (MS) and standard deviation (SD) did not change significantly with age. Response function analysis indicated that (a) climate accounts for a high amount of variance in tree-ring widths; (b) tree-ring growth has significant positive correlation with mean monthly air temperature of previous October and November, and with total monthly precipitation of current January and June, while has significant negative correlation with mean monthly air temperature of current May; and (c) AGC-2, AGC-3 and AGC-4 have stronger response to climate change than AGC-1 and AGC-5. The ANOVA F-test showed that generally there are significant differences between the first age class and other four age classes, but among the four classes in which trees are older than 200 years, the differences are usually insignificant. Overall the long-lived Qilian Juniper is still an ideal tree species for dendroclimatic reconstruction.