Characteristics of a multi-species conifer network of wood properties chronologies from Southern Australia

Progress in quantitative wood anatomy has resulted in a growing number of increasingly understood proxies from the tree-ring archive. Much of this work has been based on tree species in the Northern Hemisphere. Here, we present and examine a relatively dense network of wood property chronologies (wood density, tracheid radial diameter, cell wall thickness and ring width) from several species in Tasmania, southern Australia. We ask how the relationships amongst the different types of chronologies differ within and amongst species. We also consider how each chronology responds to monthly climate. In general terms, and similar to findings in the Northern Hemisphere, relationships between the various wood properties and climate are stronger than those between climate and ring width chronologies. An important exception to this is the highest elevation Lagarostrobos franklinii site. Additionally, strongest response to climate for the wood properties generally occurs for the concurrent growing season compared to the prior growing season for ring width. Relationships amongst the various chronology types differ for the various species, with L. franklinii also showing some variation in these relationships by site (possibly associated with elevation). Results suggest there is considerable value in further exploring the potential for developing anatomical wood chronologies for climate reconstruction from other species for which ring widths do not exhibit a strong climate signal.     

A dendroclimatic analysis of mountain hemlock (Tsuga mertensiana) ring-width and maximum density parameters,southern British Columbia Coast Mountains,Canada

The growth of mountain hemlock trees in Pacific North America demonstrates a complex relationship to two or more seasonal environmental variables. In order to examine the radial growth response of mountain hemlock to subseasonal climate variables, ring-width and X-ray densitometric analyses were used to construct intra-annual dendroclimatic records. The intent was to highlight the difference between the dendroclimatic outcomes of standard ring-width analyses to those derived from density chronologies collected at high elevation locations in the British Columbia Coast Mountains. This study highlights the importance of using multiple tree-ring parameters to better define the complex growth behaviour in mountain hemlock trees for the construction of more robust proxy climate records. Tree-ring chronologies from three sites were used to describe the inherent climate-growth trends. Maximum tree-ring density values provided a robust data series for constructing site-specific proxy records of late-summer temperature. Annual ring-width measurements provided independent proxies of spring snowpack trends. Significant decreases in temperature and an increase in snowpack depth during the early 1700s and early 1800s coincides with documented PDO phases and Little Ice Age glacier advances. Identification of early and late growing season climate signals within mountain hemlock trees demonstrates the value of documenting the characteristics of multiple tree ring parameters in future dendroclimatic studies.     

An investigation of the snowpack signal in moisture-sensitive trees from the Southern Canadian Cordillera

Variations in mountain snowpack in the western Canadian Cordillera have widespread and important impacts on ecosystems, environmental processes and socio-economic activities (e.g. water availability downstream). Historical records of snowpack generally span only the latter half of the 20th century offering a limited perspective on the causes and uniqueness of recently observed changes across the region. This paper explores the potential utility of a network of low elevation Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) tree ring-width chronologies to reconstruct past snowpack variations. Correlation coefficients between the tree-ring chronologies and a set of snow water equivalent (SWE) records are calculated and mapped. Separate analyses were carried out for total ring- width (TRW) and partial-ring measurements (earlywood and latewood; EW and LW). A set of Adjusted LW chronologies was also developed; in these, the relationship between LW and the preceding EW width has been removed. The ring-width chronologies exhibit moderately strong relationships with SWE records from the western Canadian Cordillera and these relationships vary in sign across the region. Distinctive regional groups are identified where chronologies exhibit same-sign correlations with SWE, in possible accordance with the elevation and characteristics of the tree-ring chronology sample sites. The EW chronologies correlate more strongly and consistently with SWE records in regions where the growth relationship with SWE is negative. The LW chronologies, and particularly the Adjusted LW chronologies, exhibit a greater number of positive correlations with the set of SWE records. Collectively these results offer valuable insights for developing a targeted sampling and/or reconstruction strategy that can exploit these different relationships with SWE to generate more robust estimates of pre-instrumental snowpack for the region.     

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.     

Climate sensitivity is affected by growth differentiation along the length of Juniperus communis L. shrub stems in the Ural Mountains

Arctic and alpine shrubs are valuable for future dendro-ecological and dendro-climatological studies in regions where trees are sparse or absent. A commonly accepted procedure of sampling shrub stem disks is at the root collar. However many shrub studies report low inter-series correlations in radial measurements as compared to trees. Many studies also report cross-dating difficulties with radial measurements from shrubs within a stand and commonly attribute this to differential growth along the length of the stem. So does one stem disk entirely represent the environmental parameters the shrub might be reacting to? Does change in sampling location of the stem disk affect the subsequent ring-width chronologies and climate sensitivity? To tackle these questions, we investigated Juniperus communis L. – a species wide spread in the circumpolar arctic – across a latitudinal gradient in the Ural Mountains. Based on traditional radial ring-width measurements we assessed growth synchronicity along the length of shrub stems. We also compared ring width chronologies representing different stem heights with respect to their relationships with temperature and the standardized precipitation evapotranspiration index (SPEI). Growth patterns often varied significantly among stems disks of the same shrubs, resulting in dissimilar climate-growth relationships of stem disk chronologies. For correlations with temperature, stem disks at 20 cm distance from the root collar captured the best signal. For correlations with SPEI data we could not find any specific stem disk chronology with highest sensitivity. At least in our dataset, no “perfect sampling height” with high climate sensitivity exists and our results thus highlight that a single stem disk from a shrub may not completely represent the shrub’s growth response to climate parameters.     

黑龙江漠河兴安落叶松与樟子松树轮生长特性及其对气候的响应

树木年轮 (简称树轮 ) 气候学是监测与重建全球气候变化的重要方法之一。针叶树树轮的生长能反馈出气温的变化, 在高纬度地带尤为明显。该文分析了生长在我国最北部的兴安落叶松 (Larixgmelinii) 与樟子松 (Pinussylvestrisvar.mongolica) 的树轮密度和宽度的特性。落叶松最大密度、晚材平均密度、早晚材宽度和轮宽都远高于樟子松。樟子松的所有密度变量的样本方差都明显高于兴安落叶松, 宽度变量的样本方差却明显低于兴安落叶松。两树种密度变量的差值年表显著相关, 宽度变量之间没有显著相关关系。落叶松与樟子松的晚材密度的形成受 7、8月的最高温控制。另外, 樟子松的晚材还与生长季节的长短相关。落叶松的年轮宽度对生长季节开始前的温度敏感, 而樟子松的轮宽对气候变量没有很好的响应。结果表明, 落叶松与樟子松的树轮最大密度都与生长季后期的温度显著相关, 两树种的树轮信息对气候变化的重建有很大的潜力。     

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。     

Spatiotemporal variability of tree growth and its association with climate over Northwest China

Understanding spatiotemporal tree growth variability and its associations with climate can provide key insights into forest dynamics in the context of global climate change. Here, we conduct a comprehensive investigation on 64 ring-width chronologies across the entire Northwest (NW) China to understand the regional patterns of tree growth and climate–growth relationships. Using rotated principal component analysis and hierarchical clustering analysis, we found that tree growth was mainly determined by the climate and could be classified into nine groups. Most of the tree-ring chronologies in NW China showed high correlations with moisture conditions in the current and previous growing seasons. After removing age-related growth trends, inter-annual tree growth patterns are supposed to be mainly determined by climate and climate–growth relationships. Since climate–growth relationships for most tree-ring chronologies in this arid region are similar, patterns of tree growth are mainly determined by climate variability. Within each group, the strength of the common signal increases under extreme climate conditions. Thus, climate plays a more important role in determining tree growth in extreme climate conditions relative to the non-climate factors, leading to more coherent growth patterns.     

A comparison of some simple methods used to detect unstable temperature responses in tree-ring chronologies

Temporal stability of the relationship between a potential proxy climate record and the climate record itself is the foundation of palaeoproxy reconstructions of past climate variability. Dendroclimatologists have spent considerable effort exploring the issue of temporal instability of temperature records at high-latitude and −altitude Northern Hemisphere sites. Much of this work has focused on the Divergence Problem in which the modern ends of tree-ring chronologies exhibit pronounced departures from the climate-proxy relationships of preceding decades. However, there has been little scrutiny of how different methods might influence determinations of temporal instability at either the local scale or across broader spatial domains. Here we use four sets of Southern Hemisphere (SH) chronologies and three sets of synthetic data with known interventions to compare four methodologies that have been widely used to assess the temporal stability of relationships between tree-ring series and climate. Our analyses demonstrate that a determination of temporal instability may be partially dependent on method used to examine data, that some methods are more sensitive to standardisation choice than others, and that all methods are better at detecting high- rather than low-frequency instability. In all cases, the relatively modest strength of the relationships between the selected SH ring-width chronologies and temperature is likely to be an issue, especially if changes in trends are of interest. We recommend that robust assessment of temporal instability between tree-ring chronologies and observational climate data should use a range of methods and that unstable temporal relationships across space be carefully considered in the context of large climate field reconstructions.     

Influence of larval outbreaks on the climate reconstruction potential of an Arctic shrub

Arctic shrubs have a strong potential for climate and environmental reconstructions in the chronically understudied regions of the high northern latitudes. The climate dynamics of these regions are important to understand because of large-scale feedbacks to the global climate system. However, little is known about other factors influencing shrub ring growth, possibly obscuring their climate signal. For example, as of yet we are not able to differentiate between herbivory or climatically induced growth depressions. Here, we use one of the most common Arctic shrubs, Alnus viridis as a test case to address this question. We sampled Alnus in Kobbefjord, Greenland, measured shrub-ring width and cell wall thickness and built site chronologies of each parameter. We analysed climate-growth relationships, tested their stability over time and employed a pointer-year analysis to detect growth depressions. We employed bootstrapped transfer function stability tests (BTFS) to assess the suitability of our shrub chronologies for climate reconstruction. Correlations with climate data showed strong significantly positive and stable correlations between summer temperature and ring-width with the exception of the recent decade. A climate reconstruction model failed stability tests, when the complete period of record was used for calibration and verification. Wood anatomy analysis uncovered the occurrence of unusual cell structure (very thin cell walls) in the exceptionally narrow ring of 2004, a recorded insect outbreak year in other parts of Greenland. When excluding the affected ring and a recovery period, the reconstruction model passed all tests, suggesting that the unusual 2004 ring was not climate driven, but rather the result of an insect attack. When combining anatomical analysis with traditional ring-width measurements, we move a step further in potentially distinguishing small rings caused by insect attacks from small rings formed in climatically challenging years. While this study does not provide unambiguous evidence, it does provide potential useful methodological combinations to enable more robust climate reconstructions in areas where climatic records are extremely sparse.     

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。     

天山东部西伯利亚落叶松树轮生长对气候要素的响应分析

天山东部西伯利亚落叶松的树木年轮学研究可以看出：森林上限树轮宽度年表之间相关性较高而下限年表间相关稍低,表明下限小生境要素对树木生长干扰较大。森林上下限树轮年表中样本的总解释量（ESP）和信噪比（SNR）都比较高,说明树木中都含有较多的环境信息;但标准年表中平均敏感度（M．S．）和轮宽指数的标准差（S．D．）都是森林上限数值低于下限,这表明森林上限树木生长对环境变化响应的敏感性降低;相关分析和响应分析也发现森林下限生长的树木对气候因子的响应较为显著。就温度而言,森林上限和下限表现基本一致,树木生长多与温度负相关,其中下限树木生长与春季均温和3．6月份均温显著负相关;降水表现出一定的差别,上限树木生长与春季、夏季及年降水量有较高的负相关,而对下限树木生长影响最大的则是冬季和3—6月份降水。湿润指数与降水基本一致即上限呈负相关而下限正相关,温暖指数全为负相关,寒冷指数下限负相关显著;显然该地区森林上下限树木生长的生态模式存在着一定的差异。研究发现,冬春季节的不同水热组合则是形成树木年轮宽窄的限制因素;同时,前期生长的滞后效应对年轮形成有重要的影响。     

A tree-ring densitometric transect from Alaska to Labrador

We describe a recently completed network of densitometric tree-ring time series representing various aspects of tree-growth for up to 200 years at 69 sites spread across the northern North American conifer zone from Yukon to Labrador. Duplicate cores, from 12 to 15 trees per site, provide time series for a suite of growth parameters including earlywood (spring), latewood (summer) and total (annual) ring widths and mean earlywood, mean latewood, minimum and maximum ring density. These data form the basis for extensive analyses of intra- and inter-site parameter comparisons and regional climate/tree-growth comparisons. Five large-scale regional chronologies do not suggest that any anomalous growth increases have occurred in recent decades, at least on these regional scales, despite the observed changes in atmospheric composition and climate.     

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。     

A comparison of ring-width and event-year chronologies derived from white oak (Quercus alba) and northern red oak (Quercus rubra), southwestern Quebec, Canada

In dendrochronology, ring width has been a variable of choice when assessing the radial growth–climate association of tree species. We compared ring-width and event-year chronologies from a dendroclimatic perspective using both white oak (Quercus alba L.) and northern red oak (Quercus rubra L.). The study was conducted in three regions of the Ottawa valley in southern Québec. Twelve mixed red and white oak stands were selected and for each oak species, 12 chronologies were developed from tree-ring measurement and 12 others were derived using visual assessment of narrow or wide rings (event years). Ring-width and event-year chronologies gave almost identical results and revealed the prevalence of drought in the early growing season as the most influential factor in both species. This study emphasizes the utility of event-year chronologies in tree-ring studies and their comparativeness with ring width. Establishing event-year chronologies has the advantage of being faster than measuring ring width, it does not necessitate complex equipment and depending on the purpose of the study may prove to be at least comparable. The choice of species, their mean sensitivity, the ability to recognize narrow or large rings as well as the number of trees and sites to analyze may, however, be factors to consider when choosing to use event-year chronologies over the more commonly used ring-width ones.     

Topographic mediation of growth in high elevation foxtail pine (Pinus balfouriana Grev. et Balf.) forests in the Sierra Nevada, USA

Aim Climate variability is an important mediating agent of ecosystem dynamics in cold, semi‐arid regions such as the mountains of western North America. Climatically sensitive tree‐ring chronologies offer a means of assessing the impact of climate variability on tree growth across temporal scales of years to centuries and spatial scales of metres to subcontinents. Our goal was to bring practices from landscape ecology that highlight the impact of landscape heterogeneity on ecological pattern and processes into a dendroclimatic study that shows that the biophysical setting of target trees affects ring‐width patterns. Location This study was conducted at two sites near alpine treeline in the Sequoia National Park, USA (36°30′ 00′ N, 118°30′ 00′ W). Methods We collected stand information and increment cores from foxtail pines (Pinus balfouriana Grev. et Balf.) for eight tree‐ring chronologies in four extreme biophysical settings at two sites using proxies for soil moisture and radiation derived from a digital elevation model. Results Biophysical setting affected forest age–class structure, with wet and bright plots showing high recruitment after 1900 ad , but had no obvious effect on immature stem density (e.g. seedlings). Biophysical setting strongly affected ring‐width patterns, with wet plots having higher correlation with instrumental temperature records while dry plots correlated better with instrumental precipitation records. Ring‐width chronologies from the wet plots showed strong low‐frequency variability (i.e. hundreds of years) while ring‐width chronologies from the dry plots showed strong variability on multidecadal scales. Main conclusions There was a strong association between biophysical setting and age‐class structure, and with ring‐width patterns in foxtail pine. The mediation of ring widths by biophysical setting has the potential to further the understanding of the expression of synoptic‐scale climate across rugged terrain. When combined with remotely sensed imagery, a priori GIS modelling of tree growth offers a viable means to devise first‐order predictions of climatic impacts in subalpine forest dynamics and to develop flexible and powerful monitoring schemes.     

川西高原两种针叶树径向生长对气候因子的响应

基于树轮年代学手段,建立了岷江冷杉和方枝柏树轮宽度标准年表以及混合树种年表,研究川西地区理县凉台沟两种针叶树种径向生长对气候变化的响应,为全球变暖背景下该地区森林生态系统的保护与管理提供依据。结果表明:混合年表中包含了2个单个年表的共同气候信息,其信噪比和样本总体解释量均高于单个年表。与气候因子的相关分析显示,3个年表对气候要素的响应表现出较好的一致性,均对温度响应敏感,尤其是方枝柏最为敏感。相对湿度在5、10月对两树种的限制作用明显强于降水。1994年升温突变后,岷江冷杉宽度年表与月均温的相关性变化最为明显,部分月份由负相关转变为正相关,表明岷江冷杉树木径向生长对温度的响应呈现出不稳定性,但两树种径向生长呈差异性变宽趋势,对气温响应的敏感性减弱。     

Growth response of Sabina tibetica to climate factors along an elevation gradient in south Tibet

We examine the climate significance in tree-ring chronologies retrieved from Sabina tibetica Kom. (Tibetan juniper) at two sites ranging in elevation from 4124 to 4693 m above sea level (a.s.l.) in the Namling region, south Tibet. The study region is under the control of semi-arid plateau temperate climate. The samples were grouped into high- and low-elevation classes and standard ring-width chronologies for both classes were developed. Statistical analysis revealed a decreasing growth rate yet increasing chronology reliability with increasing elevation. Overall, correlation analyses showed that radial growth in S. tibetica at the study sites was controlled by similar climatic factors, regardless of elevation; these factors comprised early winter (November) and early summer (May–June) temperatures as well as annual precipitation (July–June). Slight differences in the correlation between tree growth along the elevation gradient and climate variables were examined. The correlations with early winter temperature varied from significantly positive at the low-elevation site to weakly positive at the high-elevation site, whereas the correlations between radial growth and early summer temperature increased from weakly negative at the low-elevation sites to strongly negative at the high-elevation sites. The abundant precipitation through the year may have masked variations in tree growth on different elevation aspects. Our results will aid future dendroclimatological studies of Namling tree rings in south Tibet and demonstrate the potential of S. tibetica Kom. for improving our understanding of environmental impacts on tree growth.     

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。