Infl uence of altitude and tree class on climate-growth relationships in a larch plantation in subtropical China

Precise quantifi cation of climate-growth relationships can make a major contribution to scientifi c forest management.However,whether diff erences in the response of growth to climate at diff erent altitudes remains unclear.To answer this,264 trees of Larix kaempferi from 88 plots,representing diff erent altitudinal ranges(1000-2100 m)and tree classes were sampled and used to develop tree-ring chronologies.Tree-ring growth(TRG)was either positively(dominant)or negatively(intermediate and suppressed)correlated with climate in diff erent tree classes at diff erent altitudes.TRG was strongly correlated with growing season at low altitudes,but was less sensitive to climate at middle altitudes.It was mainly limited by precipitation and was highly sensitive to climate at low altitudes.Climate-growth relationships at high altitudes were opposite compared to those at low altitudes.TRG of dominant trees was more sensitive to climate change compared to intermediate and suppressed trees.Climate factors(annual temperatures;moisture,the number of frost-free days)had diff erent eff ects on tree-ring growth of diff erent tree classes along altitudinal gradients.It was concluded that the increase in summer temperatures decreased water availability,resulting in a signifi cant decline in growth rates after 2005 at lower altitudes.L.kaempferi is suitable for planting in middle altitudes and dominant trees were the best sampling choice for accurately assessing climate-growth relationships.

基于树木年轮的北京松山地区生态气候指标的重建

利用北京松山地区油松树木年轮资料,按照树木年轮学要求和方法,建立年轮宽度年表。根据油松年表数值同温度与降水量等气候因子的相关分析结果,基于延庆1959—2007年的气象资料,建立生态气候指标——湿润指数和干燥度指数。选择油松差值年表数值对1959—2007年间松山地区的干燥度指数进行重建,并对1933—1958年的干燥度指数进行模拟,将研究结果与历史文献灾害记录及前人研究成果相对照。结果表明:松山油松对降水量的响应相对于温度更敏感;利用年表进行重建和模拟有效;松山地区气候有变干趋势,这也与全球气候变化的趋势相一致。

Temperature variations recovered from tree-rings in the middle Qilian Mountain over the last millennium

Based on the cross-dated tree-ring samples collected from the middle Qilian Moun- tain, a standard ring-width chronology had been developed, which covered the period AD 1000 to 2000. The correlations between the chronology and climatic records from the nearby meteorological stations indicated that temperature was the dominant climatic factor for tree growth at upper timberline, and the most important climatic factor for the tree growth in the area was the mean temperature from previous December to current April. The temperature variations recovered from the ring-width data showed a cold period during the “Little Ice Age” and the con- tinuous warming during the twentieth century. Comparison between the ring-width chronology and δ18O records from the Dunde ice core in the Qilian Mountain indicated that there was a con- sistent trend in both time series. A significant correlation existed between our ring-width chro- nology and the Northern Hemispheric temperature, suggesting that the climate changes in the Qilian Mountain were not only driven by regional factors, but also responsive to the global cli- mate.

Exploratory Precipitation in North-Central China during the Past Four Centuries

Two robust precipitation reconstructions were conducted by combining tree-ring chronologies, dryness/wetness indices from historical documents, and climate data from the global grid. It was found that the recurrent drought history of a region can help us understand the variability of precipitation. Several dry/wet periods during the past four centuries and potential cycles of precipitation variation were determined. Furthermore, the reconstructions are not only consistent well with each other in North-central China, but also in good agreement with variations of precipitation in northeastern Mongolia, the Longxi area in Gangsu Province and the Dulan area of Qinghai Province, and the snow accumulation of the Guliya glacier. These synchronous variations indicate that it is valuable to study various climate records, find common information and determine the driving force of climate change.

Tree-ring-based drought variability in northern China over the past three centuries

Droughts are the most frequent natural disaster in regions at the margins of the East Asian summer monsoon(EASM),which pose threats to agriculture,the economy,and human lives.However,the limitations of only approximately 60 years of meteorological observations hamper our understanding of the characteristics and mechanisms of local hydroclimate.Trees growing in the marginal region of the EASM are usually sensitive to moisture variations and have played important roles in past hydroclimatic reconstructions.Here,a 303-year tree-ring-width chronology of Pinus tabulaeformis from Mt.Lama,which is located in the junction of the Liaoning Province and Inner Mongolia,China,was used to reconstruct the May-August Palmer drought severity index(PDSI)in the marginal region of the EASM.The transfer function explains 48.0%(or 47.2%after adjusting for the loss of the degrees of freedom)of the variance over the calibration period from 1946 to 2012.A spatial correlation analysis demonstrates that our PDSI reconstruction can represent the drought variability on the northernmost margin of the EASM.The winter Asian polar vortex area index showed a delayed impact on the summer EASM precipitation in the following year.

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.

基于树轮宽度指数的过去千年美国分区降水变化数据集

重建过去千年的区域高分辨率降水变化,对理解年代–百年尺度气候的区域差异具有独特意义。本文利用美国已有的1258个树轮宽度指数年表,结合1901–2015年的月降水量资料,分析了树轮宽度与年(上年10月至当年9月)降水量变化的相关性及降水变化的空间型;在此基础上,将美国分为12个降水变化区,遴选出与各区年降水变化具有显著正相关且长度达1750年之前的树轮宽度年表632个,采用分区、分段方法构建降水重建的校准方程,重建了美国12个区的年降水变化序列。结果显示:用于重建各区降水序列的校准方程方差解释量为28.96%–91.91%(平均值58.34%);重建序列长度超过千年的区域有4个,达500–1000年的区域为3个,其余5个区均为290–500年;其中,落基山脉南部的降水重建序列长度最长,达1858年(公元122–1979年);最短的美国东北部的大湖区为291年(公元1689–1979年)。本数据集包含了重建的12个区域年降水变化序列及其误差范围、预测方差解释量及构建校准方程的样本量等统计量;可为分析年代–百年际尺度美国与北半球其他地区(东亚、欧洲等)降水变化的异同,及其与气候模态的遥相关提供数据支撑。

树木年轮轮宽年表建立方法研究进展

树木年轮以其高分辨率、准确定年、样本广泛分布且可定量等优点,在全球变化特别是气候变化研究中广泛运用。去除以生长趋势为主的噪音,建立包含所需气候信息的轮宽年表是开展树木年轮气候学研究的关键。基于轮宽年表建立理论和树木径向生长概念模型,本文综述了轮宽年表建立过程中生长趋势拟合、指数化和均值化3个阶段的主要理论方法的研究进展;并详细介绍了最为关键的生长趋势拟合方法中,目前较为传统的曲线拟合类方法,和近20年来为克服曲线拟合类方法低频信息保留问题而受到关注和发展的区域曲线类方法;认为如何准确提取轮宽低频气候信息,将是树木年轮轮宽年表建立的主要发展趋势。

Contrasting responses of net primary productivity to inter-annual variability and changes of climate among three forest types in northern China

Aims A lack of explicit information on differential controls on net primary productivity(NPP)across regions and ecosystem types is largely responsible for uncertainties in global trajectories of terrestrial carbon balance with changing environment.The objectives of this study were to determine how NPP of different forest types would respond to inter-annual variability of climate and to examine the responses of NPP to future climate change scenarios across contrasting forest types in northern China.Methods We investigated inter-annual variations of NPP in relation to climate variability across three forest types in northern China,including a boreal forest dominated by Larix gmelinii Rupr.,and two temperate forests dominated by Pinus tabulaeformis Carr.and Quercus wutaishanica Mayr.,respectively,and studied the responses of NPP in these forests to predicted changes in climate for the periods 2011–40,2041–70 and 2070–100 under carbon emission scenarios A2 and B2 of Intergovernmental Panel on Climate Change.We simulated the responses of NPP to predicted changes in future climate as well as inter-annual variability of the present climate with the Biome-BGC version 4.2 based on site-and species-specific parameters.The modeled forest NPP data were validated against values in literature for similar types of forests and compared with inter-annual growth variations reflected by tree-ring width index(RWI)at the study sites.Important Findings Inter-annual variations in modeled NPP during the period 1960–06 were mostly consistent with the temporal patterns in RWI.There were contrasting responses of modeled NPP among the three forest types to inter-annual variability of the present climate as well as to predicted changes in future climate.The modeled NPP was positively related to annual mean air temperature in the L.gmelinii forest(P<0.001),but negatively in the P.tabulaeformis forest(P=0.05)and the Q.wutaishanica forest(P=0.03),while the relationships of modeled NPP with annual precipitation for the three forest types were all positive.Multiple stepwise regression analyses showed that temperature was a more important constraint of NPP than precipitation in the L.gmelinii forest,whereas precipitation appeared to be a prominent factor limiting the growth in P.tabulaeformis and Q.wutaishanica.Model simulations suggest marked,but differential increases in NPP across the three forest types with predicted changes in future climate.