Climate–growth analysis of Qilian juniper across an altitudinal gradient in the central Qilian Mountains, northwest China

In the context of global warming, it is of high importance to assess the influence of climatic change and geographic factors on the radial growth of high-elevation trees. Using tree-ring data collected from four stands of Qilian juniper (Juniperus przewalskii Kom.) across an altitudinal gradient in the central Qilian Mountains, northwest China, we compared the radial growth characteristics and climate–growth relationships at different elevations. Results indicated that there was little difference in the tree-ring parameters of the four chronologies. Correlation analyses both for unfiltered and 10-year high-passed data of monthly climatic variables and chronologies were presented to investigate the climatic forcing on tree growth, and results revealed that the correlation patterns were consistent among the four sites, especially for high-passed data. We employed the principal components analysis method to obtain the first principal component (PC1) of the four chronologies and computed the correlations between PC1 and climate factors. The PC1 correlated significantly with winter (November–January) temperature, prior August and current May temperature, and precipitation in the previous September and current January and April, indicating that tree growth in this region was mainly limited by cold winter temperature and drought in early growing season and prior growing season (prior August and September). However, the climate–growth relationships were unstable; with an increase in temperature, the sensitivity of tree growth to temperature had decreased over the past few decades. Considering the instability of the climate–growth relationships, climate reconstructions based on tree rings in the study area should be approached with more caution.     

Tree growth and its association with climate between individual tree-ring series at three mountain ranges in north central China

Individual tree-ring series may show changed growth trends and divergent climate–growth associations even within a site, highlighting the need to examine tree growth and its climate association before building a chronology. We provided a case study for the stratification and temporal variability of tree growth and its climate associations of individual cores for three mountain ranges in north central China. Tree growth is mainly limited by moisture conditions in previous July–September and current June–August. Repeated sampling and field investigations of Picea wilsonii at Xinglong Mountain over a growth year of 2004 suggested that the growing season is from about the end of April to the end of September. It appears that the moisture conditions in previous and current growing seasons are crucial for tree growth in this region. However, a decrease in drought limitation was observed for a few tree-ring series. We thereby built the pooled chronology and sub-site chronologies with only drought-sensitive tree rings similar climate–growth relationships from the three mountain slopes. Growth disturbances of tree-ring series are detected by checking the occurrence of successively low values of the biweight series, which are treated by fitting a flexible curve.     

Individual and time-varying tree-ring growth to climate sensitivity of Pinus tabuliformis Carr. and Sabina przewalskii Kom. in the eastern Qilian Mountains, China

Individual tree-ring width chronologies and mean chronologies from Pinus tabuliformis Carr. (Chinese pine) and Sabina przewalskii Kom. (Qilian juniper) tree cores were collected and analyzed from two sites in the eastern Qilian Mountains of China. The chronologies were used to analyze individual and time-varying tree-ring growth to climate sensitivity with monthly mean air temperature and total precipitation data for the period 1958–2008. Climate–growth relationships were assessed with correlation functions and their stationarity and consistency over time were measured using moving correlation analysis. Individuals’ growth–climate correlations suggested increased percentages of individuals are correlated with certain variables (e.g., current June temperature at the P. tabuliformis site; previous June, December and current May temperature and May precipitation at the S. przewalskii site). These same climatic variables also correspond to the mean chronology correlations. A decreased percentage of individuals correlated with these climatic variables indicates a reduced sensitivity of the mean chronology. Moving correlation analysis indicated a significant change over time in the sensitivity of trees to climatic variability. Our results suggested: (1) that individual tree analysis might be a worthwhile tool to improve the quality and reliability of the climate signal from tree-ring series for dendroclimatology research; and (2) time-dependent fluctuations of climate growth relationships should be taken into account when assessing the quality and reliability of reconstructed climate signals.     

Growth decline of Pinus Massoniana in response to warming induced drought and increasing intrinsic water use efficiency in humid subtropical China

Pinus Massoniana is the most widely distributed coniferous species in southern China and one of the most distributed species for plantation in China. It is not uncertain about the responses of tree growth to the combined effects of regional drying and the increase in the intrinsic water-use efficiency (iWUE) due to increased atmospheric CO₂. This study addressed this issue by comparing the tree growth patterns as represented by three tree-ring width chronologies with climate variables and three iWUE series derived from three tree-ring stable carbon isotope discrimination chronologies (Δ¹³C) from Pinus Massoniana in Daiyun Mountain, central Fujian province of China. Among these chronologies, we reported the first tree-ring carbon isotope discrimination chronologies (Δ¹³C) from Fuzhou area spanning last 210 years. It was found that tree radial growth is mainly limited by dry condition from May to October. Growth limitation by cold condition was only found in one high altitude site (780m) in early spring and late autumn. The tree-ring carbon discrimination was enhanced under conditions with low relative humidity and sufficient sunshine in late summer and autumn. In general, the iWUE showed a significantly increasing trend since the 1850s for all the sites in response to the increase in atmospheric CO₂. However, the growth promotion of the increased iWUE on tree growth could not compensate the growth limitation caused by drought. Especially since the 1960s, a growth decline was found at two drought stressed sites at low altitudes. On the other hand, the increase in temperature of spring and autumn and iWUE has most likely enhanced tree growth at the high altitude site.     

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 response of three tree species growing at different elevations in the Lüliang Mountains of Northern China

In this study, we present the results of a dendroclimatological investigation of three coniferous tree species, Larix principis-rupprechtii, Picea meyeri and Pinus tabulaeformis, growing along an altitudinal gradient at the Lüliang Mountains in Northern China. Totally five tree-ring width chronologies were developed to explore the climate-growth responses of these tree species. No obviously regular trend associated with the increase of elevation was found by comparing the statistical characteristics of the chronologies. Correlation analysis indicated that the chronologies from lowerest to middle-high sites (SZ, BWD, BDGL and BDGP, respectively) were highly correlated, and different species from the same site showed the highest correlation. Growth–climate analysis indicated that the chronology of Larix principis-rupprechti at the uppermost site near the tree line (XWS) did not exhibit a significant response to the seasonal climatic factors, whereas the other four lower chronologies were consistently and significantly influenced by both the mean temperature from May to July and the total precipitation from March to June, regardless of tree species and elevation. The similarity of the tree growth–climate relationships of different species growing at different elevations (except that from the tree line) suggests that the trees in this region can provide common regional climate information, and combinations of multiple species (RC) are more successful in reconstructing the climate data than single species. The results of this research are very crucial for the future forest management and dendroclimatological sampling strategy in the arid to semi-arid area of northern China.     

Forward modeling analyses of Qilian Juniper <Emphasis Type="Italic">(Sabina przewalskii)</Emphasis> growth in response to climate factors in different regions of the Qilian Mountains,northwestern China

Key message

The process-based Vaganov–Shashkin model simulations accurately represent the nonlinear process of Qilian Juniper growth–climate relationship over different regions of the Qilian Mountains.

Abstract

The Qilian Mountains (QM), northeastern edge of the Tibetan Plateau (TP), is one of the most studied areas in China for tree-ring research; considerable dendroclimatic reconstructions have been carried out and a series of important achievements made over this region. However, most reconstructions were primarily based on empirical relationships between tree growth and climate factors identified through statistical analysis. Reliable information on the physiological processes of tree responses to climate change in different regions is still scarce. Here, the process-based Vaganov–Shashkin (VS) model was used to simulate regional patterns of climate–tree growth relationships using observed temperature and precipitation over the different regions of the QM. Results showed that the sequences of simulated growth curves were broadly consistent with the actual tree-ring chronologies in all three regions of the QM. VS model simulations accurately represented the effect of climatic controls on the growth of Qilian Juniper (Sabina przewalskii). VS model outputs closely corresponded to statistical relationships between tree-ring width and climate factors as well as observational physiological behavior; i.e., available water in May and June had the largest contribution to ring formation in Qilian Juniper over the QM. The simulated and actual data analyses revealed that the radial growth of trees in the western QM was more sensitive to moisture conditions in May and June, compared with growth in the central and eastern QM. Tree growth in this region is representative of large areas in northwestern China with drought conditions.

     

Tree growth–climate relationships of Juniperus tibetica along an altitudinal gradient on the southern Tibetan Plateau

The southern Tibetan Plateau forms the ecotone between forest areas and alpine steppes and thus, tree growth is expect to react sensitive to climate variability in this semi-humid region. We sampled 328 increment cores from 169 trees at two study sites at four elevations along altitudinal transects from 4,000 to 4,500 m a.s.l. to evaluate elevation-dependent tree growth–climate relationships of Juniperus tibetica. Standard dendrochronological statistical parameters like mean inter-series correlation (Rbar), expressed population signal as well as signal-to-noise ratio is not significantly correlated to elevation. Mean segment lengths and average growth rates of the tree-ring series increase with elevation. Correlation and response function analysis with available climate data indicate that elevation has no significant effect on tree growth–climate relationships. Instead, local tree growth is mainly driven by common regional climatic signals as it is also indicated by significant correlations between all chronologies over their common period of A.D. 1550–2010. Moisture variability during April–June has the highest impact on tree growth, even close to the upper tree limit.     

Significant Mean and Extreme Climate Sensitivity of Norway Spruce and Silver Fir at Mid-Elevation Mesic Sites in the Alps

Climate forcing is the major abiotic driver for forest ecosystem functioning and thus significantly affects the role of forests within the global carbon cycle and related ecosystem services. Annual radial increments of trees are probably the most valuable source of information to link tree growth and climate at long-term time scales, and have been used in a wide variety of investigations worldwide. However, especially in mountainous areas, tree-ring studies have focused on extreme environments where the climate sensitivity is perhaps greatest but are necessarily a biased representation of the forests within a region. We used tree-ring analyses to study two of the most important tree species growing in the Alps: Norway spruce (Picea abies) and silver fir (Abies alba). We developed tree-ring chronologies from 13 mesic mid-elevation sites (203 trees) and then compared them to monthly temperature and precipitation data for the period 1846–1995. Correlation functions, principal component analysis and fuzzy C-means clustering were applied to 1) assess the climate/growth relationships and their stationarity and consistency over time, and 2) extract common modes of variability in the species responses to mean and extreme climate variability. Our results highlight a clear, time-stable, and species-specific response to mean climate conditions. However, during the previous-year''s growing season, which shows the strongest correlations, the primary difference between species is in their response to extreme events, not mean conditions. Mesic sites at mid-altitude are commonly underrepresented in tree-ring research; we showed that strong climatic controls of growth may exist even in those areas. Extreme climatic events may play a key role in defining the species-specific responses on climatic sensitivity and, with a global change perspective, specific divergent responses are likely to occur even where current conditions are less limited.     

Climate–tree growth relationships of longleaf pine (Pinus palustris Mill.) in the Southeastern Coastal Plain, USA

Knowledge of tree growth/climate response relationships is important to dendroecological studies and dendroclimatic reconstructions, particularly in the Southeastern Coastal Plain where few such studies have been attempted. To this end, we developed tree-ring chronologies of total ring width, earlywood width, and latewood width from longleaf pine (Pinus palustris Mill.) at three sites in the Southeastern Coastal Plain to examine the climate–growth relationships for this tree species. The length of these chronologies is unprecedented for southern pine chronologies in the Southeast. We compared the tree-ring chronologies to monthly temperature, precipitation, Palmer drought severity index (PDSI), and Palmer hydrological drought index (PHDI) data from the pertinent climate divisions. We found that PDSI and PHDI have the highest correlation with longleaf pine growth, and the strongest relationships between longleaf pine growth and these variables occur between July and November. Precipitation in the spring and summer was also positively related to growth at all sites. The relationship between temperature and growth was the weakest among all climate variables, but warm summer temperatures had a consistent, negative relationship with longleaf pine growth. The climate signal in the latewood was generally more robust than for total ring width and earlywood width.     

Climate–growth relationships of the dominant tree species from semi-arid savanna woodland in Ethiopia

Long-term climate–growth relationships, were examined in tree rings of four co-occurring tree species from semi-arid Acacia savanna woodlands in Ethiopia. The main purpose of the study was to prove the presence of annual tree rings, evaluate the relationship between radial growth and climate parameters, and evaluate the association of El Niño and drought years in Ethiopia. The results showed that all species studied form distinct growth boundaries, though differences in distinctiveness were revealed among the species. Tree rings of the evergreen Balanites aegyptiaca were separated by vessels surrounding a thin parenchyma band and the growth boundary of the deciduous acacias was characterized by thin parenchyma bands. The mean annual diameter increment ranged from 3.6 to 5.0 mm. Acacia senegal and Acacia seyal showed more enhanced growth than Acacia tortilis and B. aegyptiaca. High positive correlations were found between the tree-ring width chronologies and precipitation data, and all species showed similar response to external climate forcing, which supports the formation of one tree-ring per year. Strong declines in tree-ring width correlated remarkably well with past El Niño Southern Oscillation (ENSO) events and drought/famine periods in Ethiopia. Spectral analysis of the master tree-ring chronology indicated occurrences of periodic drought events, which fall within the spectral peak equivalent to 2–8 years. Our results proved the strong linkage between tree-ring chronologies and climate, which sheds light on the potential of dendrochronological studies developing in Ethiopia. The outcome of this study has important implications for paleoclimatic reconstructions and in restoration of degraded lands.     

长白山东坡不同海拔长白落叶松径向生长对气候变化的响应

为了解高山林线附近树木生长对气候变化的敏感性, 选取长白山东坡火山喷发后形成的过渡性植物群落长白落叶松(又称黄花落叶松) (Larix olgensis)林为研究对象, 并建立不同海拔高度长白落叶松的3个年轮宽度年表, 研究不同生境长白落叶松径向生长对气候变化的响应, 并利用冗余分析对不同海拔的年轮指数与气候因子的关系做进一步分析。主要结果如下: (1)高海拔年轮年表的统计特征更显著, 比低海拔径向生长对气候因子的响应更加敏感; (2)高海拔径向生长主要受上年生长季前期和生长季气温的限制, 尤其是上年6月和8月气温的限制作用, 低海拔径向生长主要与降水量有关, 受当年9月降水量和当年8月帕尔默干旱指数(PDSI)的共同影响; (3)林线内树木对气候响应的敏感性强于林线外, 林线外小生境的异质性及干扰事件频发可能掩盖了树木对气候因子的敏感性, 林线下方可能是检验林线处树木生长对气候响应平均状态的最佳位置; (4)不同海拔年轮年表与气候因子的冗余分析与响应函数分析的结果基本一致, 进一步证明了冗余分析可以有效地量化树轮指数与气候因子的关系。该研究为全球变暖背景下长白山东坡长白落叶松林的管理及该区域气候重建提供了基础数据。     

Response of radial growth to climate change for Larix olgensis along an altitudinal gradient on the eastern slope of Changbai Mountain,Northeast China

AimsTo further understand the sensitivity of tree growth to climate change and its variation with altitude, particularly the growth-climate relationship near the timberline, the radial growth of Larix olgensis in an oldgrowth forest along an altitudinal gradient on the eastern slope of Changbai Mountain was investigated. MethodsThe relationships between climate factors and tree-ring index were determined using bootstrapped response functions analysis with the software DENDROCLIM2002. Redundancy analysis, a multivariate “direct” gradient analysis, and its ordination axes were constrained to represent linear combinations with meteorological elements. The analysis was used to clarify the relationship between tree-ring width indexes at different elevations and climate factors during the period 1959-2009.Important findings indicated: (1) Tree ring chronologies from high altitudes were more superior than other samples in terms of growth-climate relationship, revealing that trees at high altitudes are more sensitive to climate variation than at low sites, (2) Tree growth was mainly affected by temperatures of from before and through growing season in previous year, especially in June and August. In comparison, tree growth in the low elevation was regulated by the combination of precipitation of August and Palmer drought severity index (PDSI) of September in current year, (3) Trees growing below timberline appeared to be more sensitive to climate warming; small extents of habitat heterogeneity or disturbance events beyond timberline may have masked the response, hence the optimal sites for examining growth trends as a function of climate variation are considered to be just below timberline, and (4) Redundancy analysis between the three chronologies and climate factors showed the same results as that of the correlation analysis and response function analysis, and this is in support of previous conclusion that redundancy analysis is also effective in quantifying the relationship between tree-ring indexes and climate factors.     

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.     

Diverging growth and resilience of Pinus tabulaeformis and Pinus massoniana to droughts in north-south transition zone,central China

Climate transition zone is a sensitive area of climate change and ecological transition where forests are vulnerable to climate extremes. Extreme droughts are increasing in frequency and magnitude under climate change, resulting in structure and function changes of forest ecosystems. Here, to analyze climate-growth relationships and quantify tree resilience to extreme droughts, we developed six tree-ring-width chronologies from P. tabulaeformis and P. massoniana sampling sites in Mt. Jigong region, Central China. The results indicated that all chronologies from the two species had good consistency, precipitation in current April and mean temperature in current August or mean minimum temperature from current August to October were the main limiting factors of the two tree species growth, but the responses of P. massoniana ring-width to climatic factors was more complex than that of P. tabulaeformis. The results also showed that tree growth of 1999–2005 was the lowest growing period during 1979–2018, and P. massoniana grew better than P. tabulaeformis before 2005 and vice versa after 2005. Comparing low growth years of trees, we identified to study tree growth resilience. The calculations from 1988, 1999–2005 and 2011 drought years indicated that P. tabulaeformis had more increased resilience to extreme droughts than that of P. massoniana, and the two species had stronger ecological recovery and resilience under global warming and non-extreme drought conditions in the recent 40 years. These results have implications for predicting tree resilience and identifying tree species in heterogeneous forest landscapes vulnerable to future climate change in climatic transition zone.     

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。     

芦芽山华北落叶松(Larix principis-rupprechtii)树轮宽度年表对气候因子的响应

在芦芽山地区采集3个不同海拔的华北落叶松(Larix principis-rupprechtii),在传统去趋势的基础上,采用"signal-free"方法对拟合曲线进行修正,避免了中等频率的气候信息引起的拟合偏差,最终建立3个不同海拔树轮宽度标准年表(STD)。同时以10a为界对上述年表进行滤波处理,得到3个低频年表。年表特征值表明,随着海拔升高,年轮平均轮宽变窄,敏感性和高频信息增强,低频信息减弱,这可能与逐渐恶劣的生境有关。中、低海拔年表的低频信息更一致,中、高海拔的高频信息更接近,而高、低海拔无论是标准年表还是高频、低频年表相似性均较差。树轮气候响应分析显示,低海拔STD年表与5月最低温负相关最为显著,STD和低频年表均与5、6月份土壤温度显著负相关,说明生境暖干,树木主要受生长季的干旱胁迫;中海拔STD年表与当年5月最高温正相关最为显著,STD和低频年表与土壤温度相关均不显著,说明生境逐渐变得冷湿,生长季的低温成为树木生长的限制因子;高海拔STD年表与气象要素相关不显著,低频年表与当年4月土壤温度正相关,说明高海拔最为冷湿,并有季节性冻土分布,生长季的土壤低温成为树木生长的限制因子。因此,全球变暖的趋势将更有利于高海拔树木的生长,而低海拔树木的干旱胁迫进一步加剧。     

Effect of climate on tree growth in the Pampa biome of Southeastern South America: First tree-ring chronologies from Uruguay

Tree-ring research in the highland tropics and subtropics represents a major frontier for understanding climate-growth relationships. Nonetheless, there are many lowland regions – including the South American Pampa biome – with scarce tree ring data. We present the first two tree-ring chronologies for Scutia buxifolia in subtropical Southeastern South America (SESA), using 54 series from 29 trees in two sites in northern and southern Uruguay. We cross-dated annual rings and compared tree growth from 1950 to 2012 with regional climate variability, including rainfall, temperature and the Palmer Drought Severity Index – PDSI, the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Overall, ring width variability was highly responsive to climate signals linked to water availability. For example, tree growth was positively correlated with accumulated rainfall in the summer-fall prior to ring formation for both chronologies. Summer climate conditions were key for tree growth, as shown by a negative effect of hot summer temperatures and a positive correlation with PDSI in late austral summer. The El Niño phase in late spring/early summer favored an increase in rainfall and annual tree growth, while the La Niña phase was associated with less rainfall and reduced tree growth. Extratropical climate factors such as SAM had an equally relevant effect on tree growth, whereby the positive phase of SAM had a negative effect over radial growth. These findings demonstrate the potential for dendroclimatic research and climate reconstruction in a region with scarce tree-ring data. They also improve the understanding of how climate variability may affect woody growth in native forests – an extremely limited ecosystem in the Pampa biome.     

Age structure and climate sensitivity of a high Andean relict forest of Polylepis rodolfo-vasquezii in central Peru

For a better understanding of forest ecology, tree-ring studies can provide information on climate sensitivity, tree growth patterns and population age structure that can inform about stand dynamics such as recruitment of new individuals, and other interspecific interactions related to competition and facilitation. Little is known about the ecology of the recently identified high Andean tree species Polylepis rodolfo-vasquezii. Here, we analyzed the relationship between tree size and age of two P. rodolfo-vasquezii forest stands located in the central Peruvian Andes at 11°S in latitude, and compared their growth patterns and climate sensitivity. We measured the height and diameter of each individual tree and collected tree core samples of living trees and cross sections of dead standing trees to generate two centennial tree-ring chronology at Toldopampa (1825–2015 CE) and at Pomamanta (1824–2014 CE) sites. The dendrochronological dates were evaluated by ¹⁴C analysis using the bomb-pulse methods analyzing a total of 9 calendar years that confirm the annual periodicity of this tree species. At the Toldopampa stand most trees ranged from 70 to 80 years old, with a 190-year old individual, being an older and better preserve forest than Pomamanta, with younger trees, probably because more human disturbances due to closer village proximity. No significant relationships were found between tree age and size in the oldest stand alerting that tree diameter should not be used as a metric for estimating tree ages as a general rule. The distinct growth patterns and the size-age relationship observed at the two forests may reflect distinct histories regarding human activities such as fire and logging. Nevertheless, both the Toldopampa and the Pomamanta tree-ring width chronologies exhibited common growth patterns and shared a similar positive response to temperature of the current growing season. Overall, our study confirmed the annual radial growth periodicity in P. rodofolfo-vasquezii trees using an independent method such as ¹⁴C analyses and a strong climate sensitivity of this tree species. These findings encourage the development of an extensive P. rodolfo-vasquezii tree-ring network for ecological and paleoclimate studies in the tropical Andes in South America.     

Spatial and temporal differences in the response of Larix sibirica to climate change in the central Altai Mountains

Because climate change impacts different ecosystems and geographies in myriad ways, it is important to study how forests in different regions respond to changing climatic conditions. In northwestern China, the transition in recent decades from a warm and dry climate to a warm and wet climate is well documented. However, the response of forests to this transition is poorly understood. To better understand these changes, we collected tree-ring samples of Larix sibirica from 12 plots on the southern slope of the central Altai Mountains and established site-specific tree-ring width residual chronologies. Through hierarchical cluster analysis, we could divide the sites into two levels: high-elevation level (HEL, >1900 m) and low-elevation level (LEL, <1900 m). We then used the first principal component of each level as the regional residual chronology and performed a moving correlation analysis with climate factors (monthly temperature, monthly precipitation, scPDSI) over the period 1957–2016. We found that changes in HEL trees are mainly related to temperature: from 1957–1967, growth was positively correlated with the temperature in July of the previous year. From the 1960s to present, growth was negatively correlated with the temperature in April of current year. Since the 1980s, however, temperature in current year January has been the most important factor limiting growth. The relationship between LEL tree growth and climate has been stable throughout the period of observation, and is significantly and positively correlated with moisture. We predict that the radial growth of HEL trees will be inhibited by continued warming, whereas LEL trees will benefit from improved moisture conditions in the future. Our findings help to provide a more comprehensive understanding of the effects of climate change on forest ecosystems, and provide a scientific reference for forest management and carbon sequestration and emission mitigation policies.