云南小中甸地区丽江云杉径向生长对气候变化的响应

丽江云杉原始林是云南省香格里拉县小中甸地区的主要森林类型.本文采用树轮年代学的方法分析了丽江云杉年轮宽度对气候变化的响应;选取相对保守的结果负指数曲线或线性回归拟合生长趋势建立年表,进行了不同时间尺度的气候因素与差值年表(RES)序列的相关及响应函数分析,并利用特征年分析了产生宽窄年轮的原因.结果表明:研究区丽江云杉的径向生长与温度升高在1990-2008年存在一定的“分离现象”;上一生长季的水热状况是限制丽江云杉当年生长的主要气候因子,特别是上年7月的气温对当年径向生长具有负反馈作用,而上年7月的充足降水则促进当年的径向生长;上年生长季温度与降水变化的相反趋势是导致宽窄年轮形成的主要原因;丽江云杉的生长对帕尔默干旱指数(PDSI)的变化不敏感.     

西大别山小林海黄山松树轮宽度的气候意义

基于树轮年代学研究方法,在鄂、豫、皖交界的西大别山北坡进行黄山松研究,建立了1915—2011年的树轮宽度标准年表（STD）.结果表明： 年表中较高的平均敏感度表明树轮中含有较多的气候变化的高频信息;较高的一阶自相关系数表明树轮生长存在显著的前期生长滞后效应;高信噪比和样本解释总量暗示树轮中含有较多的环境信息.标准年表序列指数与1959—2011年间气象因子的相关分析表明,黄山松树轮宽度生长受生长季末（9—10月）温度、降水量和相对湿度的影响较大;与9—10月帕尔默干旱指数呈显著正相关. 9、10月的水热组合是影响小林海黄山松树轮生长的主要因子.
     

利用树轮揭示人类活动对柴达木盆地巴音河径流量的影响

评估人类活动对径流的影响,对区域水资源开发管理有借鉴和指导意义。利用柴达木盆地北部山区7个祁连圆柏树轮宽度数据,建立区域平均树轮宽度年表。通过对区域平均树轮宽度年表与巴音河水文站径流量进行相关、滑动相关和回归分析,模拟了巴音河1956—2002年6月天然径流量变化,进而分析出人类活动对径流量的影响。结果表明: 树轮平均年表与6月径流量的相关性最强(r=0.63,P<0.01),两者相关系数在1986年后下降;基于1956—1986年树轮平均年表与6月径流量建立的转换方程,方差解释量为50.8%;基于转换方程模拟的1987—2002年径流量均值与实际观测径流量存在显著差异,模拟均值比观测均值大3.01 m³·s^-1。上游人类活动已经对巴音河径流量的变化带来了明显的影响。因此,在巴音河流域未来水资源开发利用规划中,有必要将人类活动作为重要的影响因素加以考虑,以保障可持续的水资源利用。     

不同去趋势方法对树轮年表气候信号的影响——以卧龙地区为例

基于川西卧龙地区林线位置岷江冷杉(Abies faxoniana)的树轮宽度数据, 结合地面气象站和空间网格化气象数据, 对不同去趋势年表对气候条件的响应特征进行了比较分析。研究表明: 不同去趋势年表的气候响应特征具有很大的相似性, 具体表现为前一年9月份、当年3月份和7月份的气温, 以及前一年10-12月份的降水、当年4月份和7月份的降水对树木生长的正影响作用; 前一年11月份到当年3月份的相对湿度, 以及当年2-3月份和7-8月份的霜冻频率对树木生长的负影响作用。从不同去趋势方法对气候响应的异质性特征来看, 保守曲线、67%样芯长度步长、60年步长和90年步长的平滑样条函数去趋势年表间具有很强的相关性, 对气候响应也最明显, 特征基本一致。30年步长的平滑曲线去趋势年表与其他去趋势年表的相关性较弱, 与气候要素的相关性也明显较小。另外, 未经去趋势处理的树轮宽度年表统计参量数值要明显高于去趋势年表, 它与气候要素的相关特征也基本反映出川西卧龙地区树木生长对气候响应的基本特征。     

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。     

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。     

长白山不同海拔树木生长对气候变化的响应差异

以长白落叶松和红松为例,探讨了长白山地区不同海拔树木生长对气候变化的响应。利用长白山北坡不同海拔4个长白落叶松样点和6个红松样点的树轮宽度资料建立差值年表,通过聚类分析、相关分析和响应分析等方法,研究树木生长特征及其气候响应。结果表明:两个树种年表的平均敏感度、树轮宽度指数的年际变率、信噪比等特征值较高,反映年表含有较强的环境信息。随海拔升高,长白落叶松年表特征值呈先下降后增加的趋势,红松年表特征值则呈先增加后下降的趋势。聚类分析将长白落叶松年表分成高、低海拔两类,红松年表分成高、中、低海拔三类。树木生长对气候响应存在海拔差异。高海拔长白落叶松生长受当年气温影响;低海拔长白落叶松生长对气候存在"滞后响应"。高海拔红松不仅受降水限制,且对气温有"滞后响应";中海拔红松不仅受气温限制,且对降水有"滞后响应";低海拔红松生长主要受气温限制。     

不同去趋势方法对树轮气候信号识别的影响

树木生长受到气候因子、随年龄增长的内在生长趋势、环境干扰和其他扰动信号的影响。目前存在不同的去趋势方法对树木年轮进行去趋势以识别树木生长中的气候信号。以往的研究多基于单个方法识别树轮气候信号，而不同去趋势方法识别的树轮气候信号可能会有一定的差别。为了对比不同去趋势方法对树轮气候信号识别的影响，我们基于国际年轮数据库网站获取中国西部地区68个点的树轮宽度数据，采用最常用的"signal-free"方法（SsfCrn）、线性和负指数函数法（std）、67%样条函数法（spline）、firedman方法、以及基于经验模式分解去趋势方法（EEMD）5种去趋势方法分别建立树轮年表，并对比分析同一地点的不同年表对气候响应的异同。结果表明：不同去趋势方法得到的年表对温度、降水以及相对湿度等气候因素的响应具有明显差异。其中，SsfCrn去趋势方法建立的年表对温度（月平均温、月最低温、月平均最低温）响应中相关最高的样点在所有样点中占比最高；EEMD去趋势方法建立的年表对降水量、相对湿度和月最高温响应中相关最高的样点在所有样点中占比最高；firedman去趋势方法建立的年表对月平均最高温响应中相关最高的样点在所有样点中占比最高。研究结果表明SsfCrn，EEMD和firedman方法在识别树轮气候信号方法具有一定的优势。在不同研究区域中，不同去趋势方法建立的年表对不同气候条件响应有差异，因此选择不同的去趋势方法识别树木生长趋势，分析哪种方法可以更好的反应气候变化对树木生长的影响显得尤为重要。     

不同去趋势方法的新疆东天山高低海拔雪岭云杉树轮宽度年表对气候的响应

利用新疆东天山高低海拔雪岭云杉(Picea schrenkiana Fisch.et Mey.)年轮样本,采用样条函数法、负指数函数法和区域曲线法3种去趋势方法研制树轮宽度标准化年表,通过分析不同去趋势方法的新疆东天山高低海拔云杉树轮宽度标准化年表特征、年表与气候响应的关系和年表间在不同频域互相关,及其与其它资料对比发现:(1)3种去趋势法对东天山年表质量影响较小,低海拔树轮年表含有更多可靠的气候变化信息。(2)高海拔的雪岭云杉树木径向生长与6—9月平均气温均呈显著正相关,其中标准化树轮年表与7月平均气温相关系数达0.553(P0.01,n=58),夏季温度可能是东天山高海拔雪岭云杉径向生长的主要限制因子;低海拔雪岭云杉树木径向生长与春季降水显著正相关,同时与春季平均气温显著负相关,春季高温和缺水共同作用的春旱可能是影响低海拔雪岭云杉径向生长的主导因子,且负指数函数年表对气候响应更敏感。(3)区域曲线法能够保留树轮标准化年表中更多低频信息,但优势不明显。高低海拔标准化年表在低频域相关系数较大,并和历史干旱事件有很好的对应。在东天山高低海拔雪岭云杉的去趋势方法研究中,负指数函数法比样条函数法和区域曲线法更适合。     

中国祁连山西段青海云杉树轮密度记录的气候信号

树轮气候学是研究过去气候变化的重要手段之一。以往研究表明,树轮密度是生长季温度的重要代用资料。本文建立了祁连山西段青海云杉132～135年的树轮最大密度年表、树轮最小密度年表、树轮晚材平均密度年表和树轮早材平均密度年表,比较了不同密度年表指示的最优气候信号及其季节组合,评估了其作为气候代用资料的潜力与价值。结果表明:树轮晚材平均密度和树轮早材平均密度对于树木生长季气候信号的响应远低于树轮最大密度和树轮最小密度;树轮早材平均密度和树轮最小密度与帕尔默干旱指数有很强的联系,表明树轮早材平均密度和树轮最小密度有成为干旱代用指标的潜力。     

detrendeR – A Graphical User Interface to process and visualize tree-ring data using R

In this paper, we present the package detrendeR, a Graphical User Interface to facilitate the visualization and analysis of dendrochronological data, using the R computing environment. This package offers an easy way to perform most of the traditional tasks in dendrochronology: detrending, chronology building and graphical presentation of time series. The advantage of detrendeR, compared with the program ARSTAN, is the graphical interface that provides the user with an easy way to use R language, rich in graphics and handling routines, with no need to type commands. The detrendeR uses a simple and familiar dialog-box interface and it can read Tucson decadal-format files (*.rwl and *.crn) as well as plain text files. In addition, detrendeR has the ability to test temporal changes of the common signal using moving intervals. The detrendeR should make it easier to perform detrending and chronology building of tree-ring series, taking advantage of the R statistical programming environment.     

The effect of end-point adjustments on smoothing splines used for tree-ring standardization

The cubic smoothing spline has been a popular method for detrending tree-ring data since the 1980s. The common implementation of this procedure (e.g., ARSTAN, dplR) uses a unique method for determining the smoothing parameter that is widely known as the %n criterion. However, this smoothing parameter selection method carries the assumption that end point effects are ignorable. In this paper, we complete the mathematical derivation and show how the original method differs from the complete version, both in the interpretation of the smoothing parameter and in the spline fit. Frequency response curves (FRC) demonstrate how the smoothing parameter is affected by the original assumption. For example, the FRC results indicate that a tree core of 250-year length has a 14% difference in the cut-off frequency when looking at the 67%n criterion. The FRC analysis shows that the existing approach produces a more flexible fit than anticipated, i.e., it is removing more variance than previously thought. For example, a 67%n spline under the existing approach corresponds to a 53%n spline fit. By using both simulated tree-core sequences and a dataset from a Midwest forest, we discuss which conditions result in greater differences between the spline fits and which conditions will have small differences. Tree-core sequences that have more curvature, such as a large-amplitude growth release, will lead to greater differences. Finally, we provide approximations to the end-point effect procedure. For example, using an 83%n criterion under the original approach produces a spline fit approximating the 67%n fit under the complete approach. These approximations could be easily implemented within existing programs like ARSTAN.     

Does signal-free detrending increase chronology coherence in large tree-ring networks?

Over the past decade, dendrochronologists have increasingly adopted the signal-free detrending (SFD) method to remove age-size trends in tree-ring measurement series, amplify the common stand-wide signal in composite chronologies, and recover medium- to low-frequency patterns that may be inadvertently removed by other detrending approaches. However, since its introduction in 2008, no systematic evaluation of the effects of SFD on tree-ring chronologies has been performed. Here we conduct the first review of SFD in dendrochronology and assess its effects when applied to large tree-ring networks. We analyzed the PAGES North America 2 K database of nearly 300 temperature-sensitive chronologies and the Missouri River database of over 350 chronologies curated for the purpose of reconstructing Missouri River streamflow. Both databases contain multiple versions of each chronology generated by different detrending methods, including those produced with (and without) the signal-free procedure applied. We evaluated (i) whether SFD increases chronology coherence at the site level by boosting the between-tree agreement, (ii) whether SFD increases coherence on a regional basis by making neighboring chronologies more similar to each other, and (iii) whether signal-free chronologies retained more medium- to low-frequency variability than their traditional counterparts. We find that, while SFD increased the strength of common signals in many instances, the effect was not universal and some sites even show a decrease in signal coherence. At regional scales, SFD increases chronology coherence in temperature-sensitive records but had no detectable effect on moisture-sensitive records. Our results demonstrate the importance of evaluating the effects of SFD prior to deploying this method for chronology development and paleoclimate reconstruction.     

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。     

大兴安岭北部樟子松树木生长与气候因子的关系

 在大兴安岭北部漠河(MH I、MH II 2个样点)、塔河蒙克山(MKS)、满归(MG)地区共采集樟子松(Pinus sylvestris var. mongolica)年轮样芯139个, 成功地建立了MH I、MH II、MKS和MG 4个样点的樟子松差值年表, 最长达377年(1631–2007年, 有效年表为1743–2007年)。樟子松年轮指数与气候因子的响应函数分析表明, 气温是这4个样点樟子松径向生长的主要限制因子。但4个样点限制其生长的月份有所差异, 漠河的2个样点樟子松年轮指数与6月气温负相关, 满归和塔河蒙克山樟子松年轮指数与前一年10月气温正相关。樟子松年表与区域气候的冗余分析(redundancy analysis, RDA)基本与响应函数分析的结果一致, 进一步验证了气温对大兴安岭北部樟子松生长的限制作用。该研究为全球变暖下大兴安岭北部樟子松林的经营管理及区域气候重建提供了基础数据。     

Development of tree-ring maximum latewood density chronologies for the western Tien Shan Mountains,China: Influence of detrending method and climate response

Three tree-ring maximum latewood density chronologies were developed from high elevation Picea schrenkiana sites in the western Tien Shan Mountains using different detrending methods. The new chronologies extend back to the early 16th and late 17th centuries, and contain significant late spring and summer temperature signals, respectively. An assessment of varying detrending methods and band-pass filtering the chronologies revealed only slightly differing low frequency trends retained in the maximum latewood densities. The distance between sampling sites and the varying seasonality of limiting climatic factors are identified as key drivers affecting the correlation among the maximum latewood density records in the study region. The new chronologies represent reliable proxies of high elevation late spring and summer temperature variability in an area underrepresented by such data, and are ready-to-use for network analyses addressing longer-term climate variations in eastern central Asia.     

川西米亚罗林区不同海拔岷江冷杉生长对气候变化的响应

为分析青藏高原东缘半湿润区树木生长与气候关系随海拔变化的规律,于川西米亚罗林区分别在高、中、低海拔选取3个采样点,共采集132棵岷江冷杉年轮样芯,建立了最长达170a(1842-2011年)3个海拔高度的差值年表.岷江冷杉年轮指数与气候因子的相关分析表明:随海拔高度降低,温度与生长的负相关呈增加趋势.高海拔岷江冷杉径向生长与前—年冬季最低温呈显著正相关,中低海拔与当年春季均温、最高温和年均最高温呈显著负相关.低海拔岷江冷杉与当年4月降水呈显著正相关,随海拔升高降水与岷江冷杉生长的相关性降低.中低海拔岷江冷杉年表与4、5月帕尔默干旱指数(P DSI)呈显著正相关,表明在中低海拔存在春季干旱胁迫,抑制了岷江冷杉的生长.另外,大龄树木比小龄树木对气候变化的响应更敏感.     

Dendrochronological potential of the Azorean endemic gymnosperm Juniperus brevifolia (Seub.) Antoine

Tree-ring inter-annual pattern variation is crucial in dendrochronology, allowing the identification of possible limiting factors on growth. Thus, trees exposed to subtropical or tropical climates without a marked seasonality may show a low degree of interannual variation, impeding a straightforward dendroclimatological approach. Meanwhile, subtropical regions, and areas in transitional climates such as the Azores archipelago, are widely unexplored in terms of dendroclimatology, providing opportunities to work with endemic trees, including the dominant Azorean tree Juniperus brevifolia (Seub.) Antoine. To evaluate the dendrochronological potential of J. brevifolia, we analyzed tree-ring patterns, crossdating capabilities, and correlation with climate parameters. We sampled 48 individual trees from two natural populations (São Miguel and Terceira islands) using an increment borer. Besides, a Trephor tool was used to obtain wood microcores for micro-anatomical analysis. Although the transition between early and latewood was evident, partially indistinct ring boundaries and wedging rings were present in some cases, affecting the crossdating process, but not impeding the establishment of reliable ring-width chronologies. Following detrending, master chronologies were built and correlated with monthly temperature and precipitation data using the treeclim R package. The climate-growth relationships indicated negative correlations with late summer temperature in both populations. Considering our results and the importance of J. brevifolia as a dominant tree in the Azores natural forests, we conclude that it shows an acceptable potential for dendrochronological research. Thus, this study provides baseline information to help fill the knowledge gap regarding the climate-growth relationship of Azorean trees.