基于黄山松树轮重建华东天目山地区1809—2018年4—7月平均气温

利用浙江北部西天目山高海拔黄山松树轮样品,建立了340年的整轮、早材和晚材宽度年表,根据子样本信号强度大于0.8的标准,确定年表的可靠时段为1810—2019年,通过对年表与气候要素进行相关分析,研究了树轮生长对气候的响应。结果表明: 黄山松径向生长对气温的响应远高于对降水的响应。综合考虑原始序列和一阶差序列相关分析结果,发现早材宽度与上年生长季前期平均气温、平均最高气温显著相关,晚材宽度与上年5月和当年9月平均气温、平均最高气温显著相关。整轮响应时段与早材较为一致,但相关性较低。最优相关组合为早材宽度与上年4—7月平均气温。基于这一关系,重建了华东天目山地区1809—2018年4—7月平均气温,方差解释量达61.5%,原始序列和一阶差序列均通过分段检验。重建气温序列中的偏冷时段为1834—1964年,偏暖时段为1809—1833和1965—2018年。20世纪60年代以来,气温进入快速上升阶段,从低频趋势上看,20世纪80年代之后气温达到过去210年来的最高水平。空间相关分析表明,重建序列较好地代表了华东地区气温的变化情况,与华东地区的区域重建序列对比也具有较好的一致性。黄山松在华东地区古气候重建方面具有较大潜力。     

1801年以来河南尧山地区油松高温变化及影响机制

基于建立的河南尧山地区油松树轮宽度标准年表,分析了油松径向生长与该地区气温、降水等气候因子之间的关系以及气温升高前后树木生长与平均最高气温间的相关性,结果表明:4—7月平均最高气温与树轮年表的相关系数高达-0.64,是该地区油松径向生长的主要限制因子;气候变暖后树轮年表与9、10月份平均最高气温显著正相关,与2、3月降水显著正相关,与4—7月平均最高气温间的相关性较为稳定。因此,重建了尧山地区1801年来4—7月平均最高气温,其方差解释量达40%(调整自由度后为38.9%)。过去216年的高温重建历史中经历了6个较暖的时期:1801—1825,1845—1853,1876—1889,1922—1944,1957—1975,1996—2013年和5个较冷的时期:1826—1844,1854—1875,1890—1921,1945—1956,1978—1995年,其结果与过去伏牛山龙池曼地区5—7月温度重建序列具有很好的一致性。周期分析结果发现该地区4—7月平均最高气温变化存在着2—4年(ENSO周期)和35.23—48.47年的主要变化周期,小波分析发现在1920年前后气候由长周期变为短周期变化;空间相关分析显示重建的高温序列很好地代表了豫东平原地区的温度变化,同时也发现与北太平洋副热带高压850 hPa上空的温度有非常高的正相关关系,表明豫东高温的波动可能与北太平洋海气振荡有关,这一研究结果为山区森林管理及平原区农业生产提供基础服务数据。     

基于树轮宽度数据重建的阴山东部过去399年降水变化

基于阴山东部油松树轮样芯,建立采样区域树轮宽度年表,并计算器测时期(AD 1952—2007)月均温和月降水量与树轮宽度年表的相关系数。结果表明: 树轮宽度年表与上一年9月至当年6月降水量变化的相关性最高(r=0.73,n=56,P<0.01),基于此重建了阴山东部过去399年(AD 1619—2017)上一年9月至当年6月的降水量变化历史。该重建解释了器测时期上一年9月至当年6月降水量54.9%的方差,经“留一法”交叉验证和分段独立检验证明,重建方程稳定可靠。在年代际尺度上,过去399年存在4个湿润时期(AD 1619—1663、AD 1705—1711、AD 1945—1963和AD 1979—2017)和4个干旱时期(AD 1734—1767、AD 1786—1814、AD 1839—1867和AD 1888—1942)。其中,AD 1979—2017是最湿润的时期,而AD 1888—1942是干旱持续最长的时段,包含最干旱时期1920s晚期。功率谱分析显示,过去399年该区降水具有2～7年和125年准周期变化。通过与邻近区域重建对比及空间相关分析表明,本降水重建序列可以较好地代表研究区域的降水变化。     

基于油松树轮重建陕西省镇安县165年以来3—4月平均最高气温

采集木王国家森林公园的油松树轮样芯,建立树轮宽度标准化年表(STD),与镇安气象站的气候因子进行相关分析,利用线性回归分析重建了镇安县1853—2017年(165年)3—4月平均最高气温。结果表明: 树轮序列与3—4月平均最高气温相关性最大(r=0.596,n=60,P<0.01)。3—4月平均最高气温重建方程的方差解释量为33.2%,重建方程稳定可靠,结果可信。重建序列中偏暖年份出现25次,偏冷年份出现29次,偏暖年份较多地伴随着洪涝事件,偏冷年份较多地伴随着干旱事件。重建序列存在明显的冷暖变化,存在2个偏冷时期(1902—1917年、1953—2000年)、4个偏暖时期(1868—1892年、1917—1937年、1941—1953年、2001—2012年)。重建序列有明显的2～7、8～15、18～28、75～96、100～125年周期变化特征,其中准113、88、22年的周期变化分别为时段内的第一、第二及第三主周期,这些周期性变化可能与太阳活动、季风和厄尔尼诺-南方涛动的变化存在一定的关系。     

近144年来秦岭太白山林线区3-6月平均气温的重建

秦岭太白山林线植被因海拔较高且受人为扰动较轻,对气候变化的响应尤为敏感,为获取过去气候变化信息提供了可靠代用资源。然而,结合树木年代学方法及Arcgis空间插值功能进行秦岭林线气候变化重建的工作至今仍处于空白。利用采自太白山林线地带太白红杉(Larix chinensis)所建立的树轮宽度资料,与提取自太白山保护区气温栅格数据中的采样点位置气象数据进行相关分析。结果表明,太白红杉与3—6月平均气温相关性最显著,采用线性回归建立了两者的拟合模型,剔除重建方程中的1997、1998年之后,方差解释量达57.2%(调整自由度后为55.5%);重建气温序列显示偏冷时段平均跨度(16年)较偏暖时段平均跨度(10.8年)长,偏冷时段有:1870—1881年、1903—1918年和1977—1996年;偏暖的时段有:1882—1892年、1919—1929年和1997—2013年;在1931—1978年这一时期,气温相对稳定,1988年之后升温强烈;周期分析显示近144年以来3—6月气温存在22—31 a,18—22 a以及10—13 a的3个振荡周期,可能与大尺度气候驱动及太阳活动存在联系。以上结果均得到历史记录以及周边重建结果的支持。     

雅鲁藏布江黑颈鹤越冬地气温时空变化特征

利用雅鲁藏布江黑颈鹤越冬地周边13个气象站点1980—2015年气温资料,对雅鲁藏布江黑颈鹤越冬地年际气温和越冬期气温变化进行研究。结果表明:1980—2015年,越冬地年平均气温、年平均最高气温和年平均最低气温均呈极显著增加趋势,越冬期气温年际变化波动振幅相对全年平均变化较大。其中越冬期最高气温增温速率最快,较年际增暖率高0.09℃/10a。越冬地年气温和越冬期气温增温速率变化趋势在空间上表现较为一致。越冬期平均气温、最高气温和最低气温的周期变化较全年均有所提前,存在一个2年的周期振荡。越冬期平均气温、平均最高气温、平均最低气温在统计时段内发生了突变,突变年份分别为1995年、1998年、1993年,气温日较差没有发生突变,越冬期气温和越冬期气温突变的方向除气温日较差以外都是由冷位相到暖位相突变。开展雅鲁藏布江黑颈鹤越冬分布区气候变化的长期监测,对于分析和精准识别气候变化对黑颈鹤越冬地分布区生境的影响,强化对黑颈鹤越冬地的保护研究有着重要的意义。     

基于红松树轮重建小兴安岭南麓过去140年6月份平均温度变化

基于建立的小兴安岭南麓红松树轮宽度标准年表,分析红松径向生长与该地区温度和降水间的关系以及1982年升温突变对此相关性的影响。结果表明：6月平均温度与树轮宽度年表在变暖前后始终呈极显著负相关,是该地区红松径向生长的主要限制因子。基于此构建的区域1843—1982年6月平均温度重建方程稳定可靠。重建温度序列的偏暖时期和偏冷时期分别持续7年和29年,偏暖时段为1915—1921年,偏冷时段为1880—1891年和1932—1948年。小波分析结果显示6月平均温度存在2—7a周期变化。空间相关分析结果表明重建温度序列能很好的代表小兴安岭南麓及附近区域的温度变化。本研究拓展了研究区现有的气候数据,可为掌握小兴安岭气候变化规律和科学预测未来气候提供数据支撑。     

昌岭山两个优势树种径向生长对气候变化的响应

在气候变暖背景下,树木径向生长对气候变化的响应存在不稳定性。利用采自祁连山东部余脉昌岭山两个优势树种油松和青海云杉的树轮样芯,建立树轮宽度标准年表,通过分析树轮宽度年表与气候要素的相关关系,探讨两个树种径向生长对气候变化的响应。结果表明：（1）油松年表比青海云杉年表包含更多的气候信息,其平均敏感度、标准差、信噪比和样本对总体的代表性等统计量均高于青海云杉标准年表。（2）气候要素对不同树种径向生长限制程度不同,油松径向生长主要与降水（前一年9月和当年3-8月）和气温（前一年9月）有关,但对降水的响应更为敏感,而青海云杉径向生长则受到气温（当年9月）和降水（前一年9月、当年3月和7月）的共同作用。（3）气温突变后,油松和青海云杉年表与各气温要素的相关性显著增强,而青海云杉年表与气温要素的相关性变化更明显,指示了青海云杉径向生长对气温的响应更不稳定。（4）生长季平均最低气温的升高诱导的干旱胁迫是油松和青海云杉树木径向生长-气温响应变化的主要原因。     

树轮记录的贺兰山区近百年来的干旱事件

利用采自东亚夏季风最北缘、地处干旱-半干旱地区的贺兰山区的树轮样芯,建立了贺兰山地区最近93年来的树轮宽度年表。与气象观测记录的相关分析结果表明,降水是限制贺兰山区树木生长的主要因素,其中5~7月份的降水与树轮宽度呈显著正相关关系,相关系数为0.522(通过95%的信度检验)。在贺兰山的树轮宽度记录中有两个主要的低生长期即20世纪20年代和70年代末到90年代末,这两个低生长期均与该区域的干旱事件相对应。通过分析还发现在干旱事件中不仅出现低降水而且同时与高气温相伴。也就是说在干旱时期内,高温和低降水的水热组合对树木影响十分显著,从而由单纯降水减少变为一种低降水高蒸发的环境,加剧了气候的干旱程度从而使树木生长出现低的生长期,形成窄轮。这种水热组合引起树轮宽度的变化对于理解过去干旱事件及其过程具有重要意义。     

太白山南北坡高山林线太白红杉对气候变化的响应差异

气候变化对秦岭植被生长的影响已经引起了人们的广泛关注,在相同的立地条件下,植被对气候变化的响应会因坡向不同而产生差异,秦岭的分水岭太白山尤为典型,为更进一步揭示不同坡向太白红杉(Larix chinensis)对气候变化响应的差异,以树木年代学为依据,利用采自太白山南、北坡相同海拔的太白红杉树芯样本分别建立了树轮年表,并分析了两者的年表特征,探讨了树轮宽度指数与气候因子之间的相关性及逐步线性回归方程。结果表明:太白山南、北坡太白红杉年表的平均敏感度、样本间平均相关系数、样本总体代表性等特征值较高,表明两个不同坡向年表中皆含有丰富的环境信息,相对而言,北坡样地植被对气候的响应较南坡样地敏感;由相关性分析可知,南北坡太白红杉差值年表对气温和降水响应显著的月份有所差异,北坡样地轮宽指数与当年和前一年1—6月平均气温皆为显著正相关关系,而南坡样地轮宽指数仅与当年5—6月平均气温通过显著性检验。南、北坡太白红杉径向生长都明显受到前一年6月降水"滞后效应"的一致影响,但北坡仅与当年8月的降水呈显著正相关,南坡与当年1—4月的平均降水量存在十分显著的负相关;多元线性逐步回归模型显示,气温因子对回归方程的贡献最大值均大于降水因子的贡献最大值,表明气温因子的变化更易引起太白红杉树轮宽度的变化,另外,气温因子对北坡样地回归模型的贡献值比气温因子对南坡样地回归模型的贡献值大,表明北坡样地处树轮宽度指数对气温因子更敏感,并且与相关分析结果一致。     

不同生境和去趋势方法下的祁连圆柏径向生长对气候的响应

利用青海不同生境祁连圆柏树木年轮样本,采用3种不同去趋势方法建立树轮年表,结合青海30个气象站的气象资料,分析不同生境和去趋势方法下祁连圆柏径向生长对气候的响应差异。结果表明,祁连山区,生长季前期的平均气温是祁连圆柏树木径向生长的主要限制性因子,NEP树轮标准化宽度年表与生长季前期冬季平均气温相关最好;在柴达木盆地,生长季降水量是该地区树木径向生长的限制性因子,SPL树轮年表对生长季降水量相关较好;在青南高原,祁连圆柏径向生长对春季温度响应最为敏感,而SPL年表与春季温度呈现明显的负相关关系,相关系数达-0.606;而在青海东部地区,祁连圆柏树木径向生长对气候的响应总体不显著。位于青海西部和北部的柴达木盆地和祁连山区祁连圆柏径向生长受西风气候的影响显著,尤其是柴达木盆地,其气候受西风主导;而青南高原受西南季风影响更为显著,该地区祁连圆柏径向生长同时受西南季风气候和海拔高度两方面影响;在青海东部,祁连圆柏径向生长受东亚季风影响更为显著。     

Maximum June–July temperatures in the southwest Yukon over the last 300 years reconstructed from tree rings

A network of seven high-elevation white spruce tree-ring chronologies from the southwest Yukon is used to reconstruct June–July maximum temperatures (T_max) back to 1684 AD, explaining 46.6% of the climatic variation over the 1946–1995 calibration period. The chronologies are characterised by low interannual ring-width variability and display similar patterns of ring-width variation across the sample area over the last 300 years. The driving force of this common signal appears to be a tree growth response to summer temperatures across the region. The reconstruction compares well with regional records of temperature variability derived from annual ring-width and maximum density data. Periods of cooler temperatures correspond with solar minima and glacier advances, particularly during the early 18th and the early 19th centuries. The maximum reconstructed temperatures are in the 1940s with 20th century values averaging 0.46 °C higher than the 1684–1899 period. In contrast to several regional studies, there does not appear to be a reduction in the sensitivity of tree growth to temperature at these sites during the late 20th century. Instead, a slight increase in the strength of the temperature–tree growth relationship is observed during recent decades. A possible explanation for this difference is the absence of significant summer season warming in the southwest Yukon region in comparison to other areas that have demonstrated this response change. This research is part of an ongoing project aimed at assessing the spatial and temporal potential of dendroclimatic reconstructions from the Yukon Territory.     

Temperature variations since the mid-18th century for western Nepal, as reconstructed from tree-ring width and density of Abies spectabilis

The climate of western Nepal was reconstructed for the past 249 years using ring width and wood density of Abies spectabilis (D. Don) Spach from western Nepal. A total of 46 increment core samples were collected from 23 individual trees growing in an open A. spectabilis stand near timberline of 3850 m a.s.l. in Humla District, western Nepal. The core samples were subjected to densitometric analysis to obtain chronologies of ring width and three kinds of intra-annual bulk densities, i.e., minimum, maximum, and mean. Response analysis of tree-ring parameters with climate records revealed that the ring width was correlated negatively with March–May (pre-monsoon) temperature and positively with March–May precipitation, while the minimum density was correlated positively with March–July temperature and negatively with March–May precipitation. On the other hand, the maximum and mean densities were positively correlated with August–September and March–September temperatures, respectively. These results indicate that the ring width and minimum density are primarily controlled by the pre-monsoon temperature and precipitation, while the latewood density by the late monsoon temperature. Finally based on these results of the response analysis, a transfer function was established, with which March–September temperature was reconstructed for the past 249 years, which shows a warming trend from 1750s until approximately 1790, followed by cooling until 1810, then by a gradual warming trend extending to 1950, and a notable cold period continuing up to the present. No evidence of a consistent warming trend over the last century or two commonly appearing in higher latitudes was found in the present reconstruction, but possible factor behind the widespread glacial retreat in the Nepal Himalayas was discussed.     

川西米亚罗林区主要树木生长对气候响应的差异

为分析青藏高原东缘半湿润区不同树种树木生长对气候变化的响应规律,于川西米亚罗林区海拔3000 m左右(低海拔)采集铁杉、岷江冷杉、紫果云杉,海拔4000 m左右林线位置(高海拔)采集岷江冷杉、四川红杉,共计182棵树木年轮样芯,建立了不同树种的树轮宽度年表,对不同树种的年轮指数与各月气候因子进行相关分析.结果表明： 在低海拔处,树木生长与4、5月气温呈负相关,与4、5月降雨呈正相关,受到春季干旱胁迫的影响;但树种之间存在显著差异： 铁杉的生长受春季干旱胁迫影响最严重,岷江冷杉次之,紫果云杉所受影响很小.在高海拔处,树木生长主要受生长季温度的影响,岷江冷杉年轮指数与当年2、7月最低气温呈显著正相关,与上一年10月最高气温亦呈正相关;四川红杉年轮指数与5月最高气温呈显著正相关,但与2月均温、3月最低气温呈显著负相关.近几十年青藏高原东北缘气候有干暖化趋势,如果这种趋势持续发生,低海拔紫果云杉长势将超过铁杉和岷江冷杉;高海拔处的升温更有利于岷江冷杉的生长.     

玉龙雪山3个针叶树种在海拔上限的径向生长及气候响应

树木生长对气候变化的响应是国内外研究的热点。选择滇西北高原玉龙雪山海拔分布上限3个主要树种(长苞冷杉(Abies georgei)、丽江云杉(Picea likiangensis)和大果红杉(Larix potaninii Batal var.macrocarpa Law)),对其径向生长特征进行研究,构建差值年表,并分析其与温度和降水的相互关系。研究结果表明:(1)温度和降水均为玉龙雪山海拔上限树木生长的主要影响因子,但不同树种响应的时期和关系存在差异;(2)大果红杉生长主要受限于生长初期(5—6月)的水热条件,主要表现为与当年5月、6月以及生长初期(5—6月)的平均温呈显著正相关,以及与当年5月、6月以及生长初期的降水呈显著负相关;(3)长苞冷杉生长主要受限于生长初期(5—6月)的水分条件,表现为显著负相关,同时生长盛期(7—8月)温度的升高有利于其径向生长;(4)丽江云杉的生长则主要受限于生长季开始以前的气候条件,与上年12月以及当年5月的平均温呈显著负相关,与当年1月的降水呈显著正相关。本研究的结果可为气候变化对滇西北高原树木生长影响的研究提供参考,并为该地区历史气候重建提供科学基础。     

Testing for tree-ring divergence in the European Alps

Evidence for reduced sensitivity of tree growth to temperature has been reported from multiple forests along the high northern latitudes. This alleged circumpolar phenomenon described the apparent inability of temperature-sensitive tree-ring width and density chronologies to parallel increasing instrumental temperature measurements since the mid-20th century. In addition to such low-frequency trend offset, the inability of formerly temperature-sensitive tree growth to reflect high-frequency temperature signals in a warming world is indicated at some boreal sites, mainly in Alaska, the Yukon and Siberia. Here, we refer to both of these findings as the ‘divergence problem’ (DP), with their causes and scale being debated. If DP is widespread and the result of climatic forcing, the overall reliability of tree-ring-based temperature reconstructions should be questioned. Testing for DP benefits from well-replicated tree-ring and instrumental data spanning from the 19th to the 21st century. Here, we present a network of 124 larch and spruce sites across the European Alpine arc. Tree-ring width chronologies from 40 larch and 24 spruce sites were selected based on their correlation with early (1864–1933) instrumental temperatures to assess their ability of tracking recent (1934–2003) temperature variations. After the tree-ring series of both species were detrended in a manner that allows low-frequency variations to be preserved and scaled against summer temperatures, no unusual late 20th century DP is found. Independent tree-ring width and density evidence for unprecedented late 20th century temperatures with respect to the past millennium further reinforces our results.     

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.     

Elevation-dependent climate sensitivity in Eucalyptus pauciflora Sieb. ex Spreng

We examine climate sensitivity in tree-ring chronologies from Eucalyptus pauciflora Sieb. ex Spreng at three elevations—1,350, 1,475 and 1,600 m above the sea level. Consistent with the principle that the sensitivity of tree-ring chronologies increases with proximity to the limits of tree growth, statistics reflecting chronology reliability increased with elevation. Climatological analyses of the three elevation classes revealed that whilst ring width is significantly and positively correlated with maximum air temperature during spring (September–November) in the chronology from the highest elevation class, significant correlations with maximum temperature are not present at low elevations. Similarly, whilst ring width in the chronology from 1,350 m was significantly and positively correlated with precipitation during late summer and early autumn, no significant correlations are evident at higher elevations. Our results illustrate the importance of careful site selection in dendroclimatological studies of eucalypts and demonstrate the potential of E. pauciflora for climatological studies.     

Crossdating and analysis of eucalypt tree rings exhibiting terminal and reverse latewood

We investigated crossdating and climate sensitivity in tree-ring series from Eucalyptus delegatensis Baker, R.T. and E. obliqua L'Herit. We first visually crossdated the measured ring width series and then independently verified this crossdating using Xmatch and cross-correlation significance tests. Crossdating was verified in 28 of the 32 study trees. Crossdating success differed between E. delegatensis and E. obliqua. In E. delegatensis crossdating success appears to be related to tree dominance and elevation. In E. obliqua radial azimuth appears to affect crossdating success. We developed two chronologies for each of the species studied. The first of these chronologies was based on all visually crossdated radii and the other on radii for which crossdating had been independently verified. Signal strength was higher in the verified chronologies. Correlation analysis between the verified chronologies and climate data revealed no significant correlation between precipitation and ring width for either species. E. obliqua ring width was significantly correlated with mean minimum and maximum air temperature and vapour pressure deficit during summer of the growing season. The E. delegatensis chronology was significantly correlated with air temperature and frequency of frost during the preceding winter. Ring width in both species was significantly correlated with air temperature during the preceding summer. Potential physiological explanations for these results are discussed. Further study is required to verify the results of climatological analysis and to explore the causes of variation in signal strength within and between trees.