Rising utilization of stable isotopes in tree rings for climate change and forest ecology

Analyses of stable isotopes(C,O,H)in tree rings are increasingly important cross-disciplinary programs.The rapid development in this field documented in an increasing number of publications requires a comprehensive review.This study includes a bibliometric analysis-based review to better understand research trends in tree ring stable isotope research.Overall,1475 publications were selected from the Web of Science Core Collection for 1974-2023.The findings are that:(1)numbers of annual publications and citations increased since 1974.From 1974 to 1980,there were around two relevant publications per year.However,from 2020 to 2022,this rose sharply to 109 publications per year.Likewise,average article citations were less than four per year before 1990,but were around four per article per year after 2000;(2)the major subjects using tree ring stable isotopes include forestry,geosciences,and environmental sciences,contributing to 42.5%of the total during 1974-2023;(3)the top three most productive institutions are the Chinese Academy of Sciences(423),the Swiss Federal Institute for Forest,Snow and Landscape Research(227),and the University of Arizona(204).These achievements result from strong collaborations;(4)review papers,for example,(Dawson et al.,Annu Rev Ecol Syst 33:507-559,2002)and(McCarroll and Loader,Quat Sci Rev 23:771-801,2004),are among the most cited,with more than 1000 citations;(5)tree ring stable isotope studies mainly focus on climatology and ecology,with atmospheric CO_(2) one of the most popular topics.Since 2010,precipitation and drought have received increasing attention.Based on this analysis,the research stages,key findings,debated issues,limitations and direc-tions for future research are summarized.This study serves as an important attempt to understand the progress on the use of stable isotopes in tree rings,providing scientific guid-ance for young researchers in this field.

Winter-spring minimum temperature variations inferred from tree-ring δ^(13)C in southeastern China

Long-term temperature variations inferred from high-resolution proxies provide an important context to evaluate the intensity of current warming.However,tem-perature reconstructions in humid southeastern China are scarce and particularly lack long-term data,limiting us to obtain a complete picture of regional temperature evolution.In this study,we present a well-verified reconstruction of winter-spring(January–April)minimum temperatures over southeastern China based on stable carbon isotopic(δ^(13)C)records of tree rings from Taxus wallichiana var.mairei from 1860 to 2014.This reconstruction accounted for 56.4%of the total observed variance.Cold periods occurred during the 1860s–1910s and 1960s–1970s.Although temperatures have had an upward trend since the 1920s,most of the cold extremes were in recent decades.The El Niño-Southern Oscillation(ENSO)variance acted as a key modulator of regional winter-spring minimum temperature variability.However,teleconnections between them were a nonlinear process,i.e.,a reduced or enhanced ENSO variance may result in a weakened or intensified temperature-ENSO relationship.

Stability assessment of tree ring growth of Pinus armandii Franch in response to climate change based on slope directions at the Lubanling in the Funiu Mountains,China

Global warming will affect growth strategies and how trees will adapt.To compare the response of tree radial growth to climate warming in different slope directions,samples of Pinus armandii Franch were collected and tree-ring chronologies developed on northern and western slopes from the Lubanling in the Funiu Mountains.Correlation analyses showed that two chronologies were mainly limited by temperatures in the previous June-August and the com-bination of temperatures and moisture in the current May-July.The difference of the climate response to slopes was small but not negligible.Radial growth of the LBLO1 site on the northern slope was affected by the combined maximum and minimum temperatures,while that of the LBLO2 site was affected by maximum temperatures.With regards to moisture,radial growth of the trees on the north slope was influenced by the relative humidity in the current May-July,while on the western slope,it was affected by the relative humidity in the previous June-August,the current May-July and the precipitation in the current May-July.With the change in climate,the effects of the main limiting factors on growth on different slopes were visible to a certain extent,but the differences in response of trees on different slopes gradually decreased,which might be caused by factors such as different slope directions and the change in diurnal temperature range.These results may provide information for forest protection and ecological construction in this region,and a scientific reference for future climate reconstruction.

Stability assessment of tree ring growth of Pinus armandii Franch in response to climate change based on slope directions at the Lubanling in the Funiu Mountains,China

Global warming will affect growth strategies and how trees will adapt.To compare the response of tree radial growth to climate warming in different slope directions,samples of Pinus armandii Franch were collected and treering chronologies developed on northern and western slopes from the Lubanling in the Funiu Mountains.Correlation analyses showed that two chronologies were mainly limited by temperatures in the previous June–August and the combination of temperatures and moisture in the current May–July.The difference of the climate response to slopes was small but not negligible.Radial growth of the LBL01 site on the northern slope was affected by the combined maximum and minimum temperatures,while that of the LBL02 site was affected by maximum temperatures.With regards to moisture,radial growth of the trees on the north slope was influenced by the relative humidity in the current May–July,while on the western slope,it was affected by the relative humidity in the previous June–August,the current May–July and the precipitation in the current May–July.With the change in climate,the effects of the main limiting factors on growth on different slopes were visible to a certain extent,but the differences in response of trees on different slopes gradually decreased,which might be caused by factors such as different slope directions and the change in diurnal temperature range.These results may provide information for forest protection and ecological construction in this region,and a scientific reference for future climate reconstruction.

Climate warming is significantly influenced by rising summer maximum temperatures:insights from tree-ring evidence of the Western Tianshan Mountains,China

As one of the regions most affected by global climate warming,the Tianshan mountains has experienced several ecological crises,including retreating glaciers and water deficits.Climate warming in these mountains is considered mainly to be caused by increases in minimum temperatures and winter temperatures,while the influence of maximum temperatures is unclear.In this study,a 300-year tree-ring chronology developed from the Western Tianshan Mountains was used to reconstruct the summer(June-August)maximum temperature(Tmax6-8) variations from 1718 to2017.The reconstruction explained 53.1% of the variance in the observed Tmax6-8.Over the past 300 years,the Tmax6-8reconstruction showed clear interannual and decadal variabilities.There was a significant warming trend(0.18 ℃/decade) after the 1950s,which was close to the increasing rates of the minimum and mean temperatures.The increase in maximum temperature was also present over the whole Tianshan mountains and its impact on climate warming has increased.The Tmax6-8variations in the Western Tianshan mountains were influenced by frequent volcanic eruptions combined with the influence of solar activity and the summer North Atlantic Oscillation.This study reveals that climate warming is significantly influenced by the increase in maximum temperatures and clarifies possible driving mechanisms of temperature variations in the Western Tianshan mountains which should aid climate predictions.

Climate warming is significantly influenced by rising summer maximum temperatures: insights from tree-ring evidence of the Western Tianshan Mountains, China

As one of the regions most affected by global cli-mate warming,the Tianshan mountains has experienced sev-eral ecological crises,including retreating glaciers and water deficits.Climate warming in these mountains is considered mainly to be caused by increases in minimum temperatures and winter temperatures,while the influence of maximum temperatures is unclear.In this study,a 300-year tree-ring chronology developed from the Western Tianshan Moun-tains was used to reconstruct the summer(June-August)maximum temperature(T_(max6-8))variations from 1718 to 2017.The reconstruction explained 53.1% of the variance in the observed T_(max6-8).Over the past 300 years,the T_(max6-8)reconstruction showed clear interannual and decadal vari-abilities.There was a significant warming trend(0.18°C/decade)after the 1950s,which was close to the increasing rates of the minimum and mean temperatures.The increase in maximum temperature was also present over the whole Tianshan mountains and its impact on climate warming has increased.The T_(max6-8) variations in the Western Tianshan mountains were influenced by frequent volcanic eruptions combined with the influence of solar activity and the sum-mer North Atlantic Oscillation.This study reveals that cli-mate warming is significantly influenced by the increase in maximum temperatures and clarifies possible driving mech-anisms of temperature variations in the Western Tianshan mountains which should aid climate predictions.

More tree growth reduction due to consecutive drought and its legacy effect for a semiarid larch plantation in Northwest China

Extreme climate has increasingly led to negative impacts on forest ecosystems globally,especially in semiarid areas where forest ecosystems are more vulnerable.However,it is poorly understood how tree growth is affected by different drought events.In 2006–2009,the larch plantations in the semiarid areas of Northwest China were negatively affected by four consecutive dry years,which was a very rare phenomenon that may occur frequently under future climate warming.In this study,we analyzed the effect of these consecutive dry years on tree growth based on the data of the tree rings in the dominant layer of the forest canopy on a larch plantation.We found that the tree-ring width index(RWI)in dry years was lower than that in normal years,and it experienced a rapidly decreasing trend from 2006 to 2009(slope=-0.139 year^(-1),r=-0.94)due to water supply deficits in those dry years.Drought induced legacy effects of tree growth reduction,and consecutive dry years corresponded with greater growth reductions and legacy effects.Growth reductions and legacy effects were significantly stronger in the third and fourth consecutive dry years than that of single dry year(p<0.05),which might have been due to the cumulative stress caused by consecutive dry years.Our results showed that larch trees experienced greater tree growth reduction due to consecutive dry years and their legacy effect,and the trees had lower recovery rates after consecutive dry years.Our results highlight that consecutive dry years pose a new threat to plantations under climate warming,and thus,the effect of climate extremes on tree growth should be considered in growth models in semiarid areas.

Aging Mongolian pine plantations face high risks of drought-induced growth decline:evidence from both individual tree and forest stand measurements

Discerning vulnerability differences among different aged trees to drought-driven growth decline or to mortality is critical to implement age-specific countermeasures for forest management in water-limited areas.An important species for afforestation in dry environments of northern China,Mongolian pine(Pinus sylvestris var.mongolica Litv.)has recently exhibited growth decline and dieback on many sites,particularly pronounced in old-growth plantations.However,changes in response to drought stress by this species with age as well as the underlying mechanisms are poorly understood.In this study,tree-ring data and remotely sensed vegetation data were combined to investigate variations in growth at individual tree and stand scales for young(9-13 years)and aging(35-52 years)plantations of Mongolian pine in a water-limited area of northern China.A recent decline in tree-ring width in the older plantation also had lower values in satellited-derived normalized difference vegetation indices and normalized difference water indices relative to the younger plantations.In addition,all measured growth-related metrics were strongly correlated with the self-calibrating Palmer drought severity index during the growing season in the older plantation.Sensitivity of growth to drought of the older plantation might be attributed to more severe hydraulic limitations,as reflected by their lower sapwood-and leaf-specific hydraulic conductivities.Our study presents a comprehensive view on changes of growth with age by integrating multiple methods and provides an explanation from the perspective of plant hydraulics for growth decline with age.The results indicate that old-growth Mongolian pine plantations in water-limited environments may face increased growth declines under the context of climate warming and drying.

Long-term changes in radial growth of seven tree species in the mixed broadleaf-Korean pine forest in Northeast China:Are deciduous trees favored by climate change?

The role of the temperate mixed broadleaf-Korean pine forest(BKF)in global biogeochemical cycles will depend on how the tree species community responds to climate;however,species-specific responses and vulner-abilities of common trees in BKF to extreme climates are poorly understood.Here we used dendrochronological meth-ods to assess radial growth of seven main tree species(Pinus koraiensis,Picea jezoensis,Abies nephrolepis,Fraxinus mandshurica,Phellodendron amurense,Quercus mongolica,and Ulmus davidiana)in an old-growth BKF in response to climate changes in the Xiaoxing’an Mountains and to improve predictions of changes in the tree species compo-sition.Temperature in most months and winter precipita-tion significantly negatively affected growth of P.jezoensis and A.nephrolepis,but positively impacted growth of P.koraiensis and the broadleaf species,especially F.mandshu-rica and U.davidiana.Precipitation and relative humidity in June significantly positively impacted the growth of most tree species.The positive effect of the temperature during the previous non-growing season(PNG)on growth of F.mandshurica and Q.mongolica strengthened significantly with rapid warming around 1981,while the impact of PNG temperature on the growth of P.jezoensis and A.nephrolepis changed from significantly negative to weakly negative or positive at this time.The negative response of radial growth of P.jezoensis and A.nephrolepis to precipitation during the growing season gradually weakened,and the negative response to PNG precipitation was enhanced.Among the studied species,P.koraiensis was the most resistant to drought,and U.davidiana recovered the best after extreme drought.Ulmus davidiana,P.jezoensis and A.nephrolepis were more resistant to extreme cold than the other species.Climate warming generally exacerbated the opposite growth patterns of conifer(decline)and broadleaf(increase)spe-cies.Deciduous broadleaf tree species in the old-growth BKF probably will gradually become dominant as warming continues.Species-specific growth-climate relationships should be considered in future models of biogeochemical cycles and in forestry management practices.

Effects of Climatic Factors on Tree-ring Maximum Latewood Density of Picea schrenkiana in Xinjiang, China

Based on two tree-ring maximum latewood density （MXD） chronologies of Picea schrenkiana from the Manas River Basin, Xinjiang, the response characteristics of MXD to climate variation was discussed. Correlation analysis between MXD chronologies and instrumental records from Shihezi meteorological station showed that each chronology was significantly and positively correlated with the maximum monthly average temperature in July-August, and especially, the regional chronology （RC） was the most highly correlated variable （r=0.54, P〈0.001）. Afterwards, the maximum average temperature in July-August was reconstructed using RC. Comparison among reconstructed temperature, observed values, and the drought index （Is） confirmed that precipitation would affect MXD when the absolute value of Is is greater than 1.5σ （｜Is｜ 〉 2.5 during 1953-2008） or near to 1.5a over a 2-3 year period. The response characteristics are related to the semiarid climate of the study area. In dry years, lack of precipitation would limit the thickening of latewood cell walls and, as a result, impact MXD. Therefore, compared with relatively humid regions, the response of tree-ring MXD to air temperature similarly would be influenced by extreme moisture conditions in semiarid areas, and MXD, as a temperature proxy, should be used prudently on a limited scale.

R软件包MtreeRing在生长轮宽度测量中的应用

介绍了使用R软件包MtreeRing自动测量生长轮宽度的方法。MtreeRing使用数学形态学和边缘检测方法对数字图像中的生长轮边界进行识别,并且可以校正倾斜生长轮带来的测量误差。此外,MtreeRing还提供了具有图形用户界面的小程序,满足了不同编程水平用户的需求。两个针叶树种的对比分析表明,MtreeRing测量的生长轮宽度与WinDENDRO无显著差异,自动检测提高了测量效率,图形用户界面也增强了R软件的易用性。相比WinDENDRO等商业工具,MtreeRing无需软件成本,生长轮宽度序列可以直接在R软件中进行后续分析,或使用rwl等通用格式导出。

Correlation Between Chemical Element Contents in Tree Rings and Soils

The annual growth rings of ten trees and the soils near the tree roots were sampled from the mining area of lead-and zinc-dominant metals in the Xixia Mountain, Nanjing, for the determination of chemical element contents. The study results showed that the elemental contents in the tree rings were correlated with those in the soils, i. e., the elemental contents in the tree rings increased with those in the soils, even in the cases of different environments and different tree species. Therefore, a time-concentration sequence could be set up on the basis of determining the elemental contents in the successive annual growth rings of trees to qualitatively reflect the annual variations of relevant elements in the soils, and a time-concentration sequence of elemental contents in soils could also be established in terms of related model to reproduce the dynamic changes of the surroundings.

Improved EEMD-based standardization method for developing long tree-ring chronologies

Long tree-ring chronologies can be developed by overlapping data from living trees with data from fossil trees through cross-dating.However,low-frequency climate signals are lost when standardizing tree-ring series due to the"segment length curse".To alleviate the segment length curse and thus improve the standardization method for developing long tree-ring chronologies,here we first calculated a mean value for all the tree ring series by overlapping all of the tree ring series.The growth trend of the mean tree ring width(i.e.,cumulated average growth trend of all the series)was determined using ensemble empirical mode decomposition.Then the chronology was developed by dividing the mean value by the growth trend of the mean value.Our improved method alleviated the problem of trend distortion.Long-term signals were better preserved using the improved method than in previous detrending methods.The chronologies developed using the improved method were better correlated with climate than those developed using conservative methods.The improved standardization method alleviates trend distortion and retains more of the low-frequency climate signals.

Chrono-Sequences of Elemental Contents in Tree Ringsand Soils

There exists a logarithmic linear correlation, i. e., In C'(Z, t) = a(Z) + b(Z) ln(Z, t) where Z is the atomicnumber of element and t the year when tree ring grows between the chemical element contents in tree ringsC(Z, t) and those in the soils near the tree roots C'(Z, t).By determining the elemental contents of the annual growth rings of trees, we could establish the chrono-sequences of elemental contents in the tree rings, thus calculating that of the soil, that is, reproducing thedynamic changes of contents of elements in the soil C'(Z, t). The background values of elements in the soilunder site conditions of the tree could be estimated from the minimum C(Z, t_0) in the chrono-sequences ofelemental contents in the tree rings.

Using a Tree Ring δ^(13)C Annual Series to Reconstruct Atmospheric CO_2 Concentration over the Past 300 Years

The annual series of δ13C were measured in tree rings of three Cryptomeria fortunei disks （OF-1, OF-2, and OF- 3） collected from West Tianmu Mountain, Zhejiang Province, China, according to cross-dating tree ring ages. There was no obvious decreasing trend of the δ13C annual time series of CF-2 before 1835. However, from 1835 to 1982 the three tree ring δ13C annual series exhibited similar decreasing trends that were significantly （P ≤ 0.001） correlated. The distribution characteristics of a scatter diagram between estimated δ13C series of CF-2 from modeling and the atmospheric CO2 concentration extracted from the Law Dome ice core from 1840 to 1978 were analyzed and a curvilinear regression equation for reconstructing atmospheric CO2 concentration was established with R2 = 0.98. Also, a test of independent samples indicated that between 1685 and 1839 the reconstructed atmospheric CO2 concentration .using the δ13C series of CF-2 had a close relationship with the Law Dome and Siple ice cores, with a standard deviation of 1.98. The general increasing trend of the reconstructed atmospheric CO2 concentration closely reflected the 10ng-term variation of atmospheric CO2 concentration recorded both before and after the Industrial Revolution. Between 1685 and 1840 the evaluated atmospheric CO2 concentration was stable, but after 1840 it exhibited a rapid increase. Given a longer δ13C annual time series of tree rings, it was feasible to rebuild a representative time series to describe the atmospheric CO2 concentration for an earlier period and for years that were not in the ice core record.

Reconstruction of hydrological changes based on tree-ring data of the Haba River, northwestern China

Reconstructing the hydrological change based on dendrohydrological data has important implications for understanding the dynamic distribution and evolution pattern of a given river. The widespread, long-living coniferous forests on the Altay Mountains provide a good example for carrying out the dendrohydrological studies. In this study, a regional composite tree-ring width chronology developed by Lariat sibirica Ledeb. and Picea obovata Ledeb. was used to reconstruct a 301-year annual （from preceding July to succeeding June） streamflow for the Haba River, which originates in the southern Altay Mountains, Xinjiang, China. Results indicated that the reconstructed streamflow series and the observations were fitting well, and explained 47.5% of the variation in the observed streamflow of 1957-2008. Moreover, floods and droughts in 1949-2000 were precisely captured by the streamflow reconstruction. Based on the frequencies of the wettest/driest years and decades, we identified the 19th century as the century with the largest occurrence of hydrological fluctuations for the last 300 years. After applying a 21-year moving average, we found five wet （1724-1758, 1780-1810, 1822-1853, 1931-1967, and 1986-2004） and four dry （1759-1779, 1811-1821, 1854-1930, and 1968-1985） periods in the streamflow reconstruction. Furthermore, four periods （1770-1796, 1816-1836, 1884-1949, and 1973-1997） identified by the streamflow series had an obvious increasing trend. The increasing trend of streamflow since the 1970s was the biggest in the last 300 years and coincided with the recent warming-wetting trend in northwestern China. A significant correlation between streamflow and precipitation in the Altay Mountains indicated that the streamflow reconstruction contained not only local, but also broad-scale, hydro-climatic signals. The 24-year, 12-year, and 2.2-4.5-year cycles of the reconstruction revealed that the streamflow variability of the Haba River may be influenced by solar activity and the atmosphere-ocean system.

Study on Model of Correlation Between Chemical Ele－ment Contents in Tree Rings and Soils near Tree Roots

The chemical element contents in tree rings are correlated with those in the soils near the tree roots. Theresults in the present study showed that the correlation between them could be described using the followinglogarithmic linear correlation model:lgC'(Z) = α(Z) + b(Z)lgC(Z).Therefore, by determining the chrono-sequence C(Z, t), where Z is the atomic number and t the year ofelemental contents in the annual growth rings of trees, we could get the chrono-sequence C'(Z, t) of elementalcontents in the soil, thus inferring the dynamic variations of relevant elemental contents in the soil.

Tree ring based drought variability in Northwest Tajikistan since 1895 AD

Determining the mechanisms controlling the changes of wet and dry conditions will improve our understanding of climate change over the past hundred years,which is of great significance to the study of climate and environmental changes in the arid regions of Central Asia.Forest trees are ecologically significant in the local environment,and therefore the tree ring analysis can provide a clear record of regional historical climate.This study analyzed the correlation between the tree ring width chronology of Juniperus turkestanica Komarov and the standardized precipitation evapotranspiration index(SPEI)in Northwest Tajikistan,based on 56 tree ring samples collected from Shahristan in the Pamir region.Climate data including precipitation,temperature and the SPEI were downloaded from the Climate Research Unit(CRU)TS 4.00.The COFECHA program was used for cross-dating,and the ARSTAN program was used to remove the growth trend of the tree itself and the influence of non-climatic factors on the growth of the trees.A significant correlation was found between the radial growth of J.turkestanica trees and the monthly mean SPEI of February–April.The monthly mean SPEI sequence of February–April during the period of 1895–2016 was reconstructed,and the reconstruction equation explained 42.5%of the variance.During the past 122 a(1895–2016),the study area has experienced three wetter periods(precipitation above average):1901–1919,1945–1983 and 1995–2010,and four drier periods(precipitation below average):1895–1900,1920–1944,1984–1994 and 2011–2016.The spatial correlation analysis revealed that the monthly mean SPEI reconstruction sequence of February–April could be used to characterize the large-scale dry-wet variations in Northwest Tajikistan during the period of 1895–2016.This study could provide comparative data for validating the projections of climate models and scientific basis for managing water resources in Tajikistan in the context of climate change.

January to August temperature variability since 1776 inferred from tree-ring width of Pinus tabulaeformis in Helan Mountain

Tree-ring standardized chronologies are developed by 78 cores collected from the eastern and western Helan Mountain. Statistical analysis shows that both the STD and RES chronologies correlate negatively with the temperature of different periods of early half year, especially with January to August mean （JA） temperature, which means that JA temperature is one of the predominant limiting factors of tree growth in the Helan Mountain. Based on this analysis, we reconstructed JA temperature, and the explained variance is 43.3% （F=21.422, p〈0.001 ）. The comparatively high temperature periods in the reconstruction were： 1805-1818 1828-1857, 1899-1907, 1919-1931 and 1968-1995; and the comparatively low temperatu re periods happened in 1858-1872, 1883-1895 and 1935-1953. Ten-year moving average curve shows three slow uplifting trends： 1766-1853, 1862-1931 and 1944-1995. Each temperature increase was followed by a sudden temperature decrease about 10 years, that is to say, the JA temperature in the Helan Mountain is characterized by slow increase and sudden decrease. The 70- and 10.77-year periodicities detected in the temperature series correspond to the Gleissberg （80-year） and Schwabe （11-year） periodicities of solar activity respectively, the 2.11-2.62 years cycles are considered to be influenced by QBO （Quasi-Biennial-Oscillation） and the local environmental change.

Tree-ring response of Larix chinensis on regional climate and sea-surface temperature variations in alpine timberline in the Qinling Mountains

Tree-ring width chronologies of Larix chinensis were developed from the northern and southern slopes of the Qinling Mountains in Shaanxi Province,and climatic factors affecting the tree-ring widths of L.chinensis were examined.Correlation analysis showed that similar correlations between tree-ring width chronologies and climatic factors demonstrated that radial growth responded to climate change on both slopes.The radial growth of L.chinensis was mainly limited by temperature,especially the growing season.In contrast,both chronologies were negatively correlated with precipitation in May of the previous year and April of the current year.Spatial climate-correlation analyses with gridded land-surface climate data revealed that our tree-ring width chronologies contained a strong regional temperature signal over much of northcentral and eastern China.Spatial correlation with seasurface temperature fields highlights the influence of the Pacific Ocean,Indian Ocean,and North Atlantic Ocean.Wavelet coherence analysis indicated the existence of some decadal and interannual cycles in the two tree-ring width chronologies.This may suggest the influences of El Nin˜o-Southern Oscillation and solar activity on tree growth in the Qinling Mountains.These findings will help us understand the growth response of L.chinensis to climate change in the Qinling region,and they provide critical information for future climate reconstructions based on this species in semi-humid regions.