Non-destructive dendrochronology with X-ray computed tomography: The influence of different conservation methods for waterlogged archaeological wood

In this study, the influence of different conservation methods for waterlogged archaeological wood (WAW) on non-destructive dendrochronological dating by micro-computed tomography (µCT) was evaluated. For this purpose, samples of different wood species were conserved using the following methods: alcohol-ether-resin, Kauramin 800®, lactitol/trehalose, saccharose, silicone oil and different polyethylene glycol (PEG) treatments with subsequent freeze-drying. The tree ring measurements of all samples in the digital µCT data were compared with the measurements on an analog linear measuring table in terms of the total number of rings per sample and the mean ring width. The year-to-year ring width measurements in the µCT data agreed very well overall with the corresponding microscopic measurements. It was possible to detect the rings in the samples with µCT in all cases. A dendrochronological cross dating with regional absolutely dated ring width chronologies was successful in two cases. However, the different influence of the conservation agents on the quality of the µCT data was clearly visible. In order to assess this influence, the contrast in the µCT data was determined using grey-scale profiles. A decrease in contrast in the µCT data was detectable for all conservation agents. A particular strong influence is observed for the conservation methods using silicone oil, lactitol/trehalose, PEG and saccharose. Overall, the study performed confirms that µCT is a powerful and accurate method for non-destructive dendrochronology of conserved archaeological objects.     

基于非刚体配准的体数据插值重建方法

三维图像的处理和操作需要将一般的断层序列插值成为具有各坐标轴一致的分辨率的体数据,而目前最常用的线性插值方法在层间距较大时会导致图像边缘模糊和出现伪影。Penney根据现有的非刚体匹配方法,提出了利用图像形变场数据的插值算法,大大提高了层间插值的质量。本文对Penney提出的算法进行了两方面的改进,在配准过程中用简单的单射性约束取代了复杂的平滑性约束,用邻域平均算法替代Penney使用的最邻近直线插值方法,并将新算法的实验结果与原算法、线性插值进行了对比,新算法在保持高质量插值的前提下提高了计算速度。该算法可以应用于精度要求比较高的体数据插值重建过程。     

基于配准的插值

断层间图像插值是三维重建的一个关键步骤,因为图像上像素之间的间隔常常小于断层图像之间的距离,而在三维重建需要它们有一致的分辨率.由于是同模态断层图像层间插值,对于解决同模态弹性配准问题,Thirion的demons算法比较适合.所以配准采用Demons方法.Demons算法先判断出待配准图像上各个象素点的运动方法,通过对各个象素点的移动来实现非刚性配准.在这个算法中,每张图像都被视为同灰度值轮廓的集合.该算法可以应用于精度要求比较高的体数据插值重建过程.     

Influence of tree hollow characteristics and forest structure on saproxylic beetle diversity in tree hollows in managed forests in a regional comparison

Tree hollows are among the rarest habitats in today''s Central European managed forests but are considered key structures for high biodiversity in forests. To analyze and compare the effects of tree hollow characteristics and forest structure on diversity of saproxylic beetles in tree hollows in differently structured managed forests, we examined between 41 and 50 tree hollows in beech trees in each of three state forest management districts in Germany. During the two‐year study, we collected 283 saproxylic beetle species (5880 individuals; 22% threatened species), using emergence traps. At small spatial scales, the size of hollow entrance and the number of surrounding microhabitat structures positively influenced beetle diversity, while the stage of wood mould decomposition had a negative influence, across all three forest districts. We utilized forest inventory data to analyze the effects of forest structure in radii of 50–500 m around tree hollows on saproxylic beetle diversity in the hollows. At these larger spatial scales, the three forest management districts differed remarkably regarding the parameters that influenced saproxylic beetle diversity in tree hollows. In Ebrach, characterized by mostly deciduous trees, the amount of dead wood positively influenced beetle diversity. In the mostly coniferous Fichtelberg forest district, with highly isolated tree hollows, in contrast, only the proportion of beech trees around the focal tree hollows showed a positive influence on beetle diversity. In Kelheim, characterized by mixed forest stands, there were no significant relationships between forest structure and beetle diversity in tree hollows. In this study, the same local tree hollow parameters influenced saproxylic beetle diversity in all three study regions, while parameters of forest structure at larger spatial scales differed in their importance, depending on tree‐species composition.     

基于枝条木材密度分级的鼎湖山南亚热带常绿阔叶林树高曲线模型

如何便捷准确地测量树高一直是林学及群落生态学所关心的问题。由于木材密度与树木生长密切相关, 因此基于木材密度建立树高曲线模型能够为测量树高提供新的方法。本文以鼎湖山南亚热带常绿阔叶林1.44 ha塔吊样地内119个物种的4,032个个体为研究对象, 利用树高、胸径和木材密度数据来探究基于枝条木材密度分级的树高曲线模型。首先, 对个体进行随机抽样, 将其划分为建模样本(占总样本量的70%)和检验样本(占总样本量的30%), 并通过聚类分析将所有个体的木材密度划分为4级。其次, 基于建模样本利用常见的5种理论生长方程(Richards、Korf、Logistic、Gompertz和Weibull方程)对不同分级建立树高-胸径模型; 基于检验样本检验模型精度, 并确定各分级的最适模型。最后, 构建基于物种分类的树高曲线模型, 并比较其与木材密度分级模型的差异。结果表明: 基于木材密度分级的模型, 各分级小组检验样本的平均绝对误差(MAE)和均方根误差(RMSE)最小值所对应的模型类型与建模样本结果一致, 确定Gompertz模型和Weibull模型为鼎湖山南亚热带常绿阔叶林最适树高模型类型。比较基于木材密度分级的模型与基于物种分类的模型, 发现二者的MAE、RMSE指数差异小。综上, 基于木材密度分级的树高曲线模型对树高估测精度高, 使用方便, 为树高预测提供了新方法, 可以更好服务森林调查等生产实践。     

橡胶树(Hevea brasiliensis Muell.Arg.)幼茎木材的超微结构观察

橡胶树是中国重要的热带经济作物,橡胶种植的副产物橡胶木是我国木材供应的重要来源。我们以不同发育阶段的橡胶树幼茎木材为材料,借助扫描电子显微镜技术,对木质部细胞的超微结构进行了观察。结果表明,在橡胶树幼茎木材中,导管和木纤维细胞壁随着木质部发育成熟会发生明显的次生加厚,加厚方式主要为螺纹加厚;木质部各类型细胞均存在大量纹孔,纹孔排列方式主要有散生、网状、梯状和单串状等类型;在木质部发育过程中,木射线和部分薄壁细胞中会逐渐积累大量淀粉粒;木质部细胞内壁及其填充物表面存在不同类型的附着物。研究结果将为橡胶木材材性及其形成机制的研究提供一定理论参考。     

Techniques for the detection of pathogenic Cryptococcus species in wood decay substrata and the evaluation of viability in stored samples

In this study, we evaluated several techniques for the detection of the yeast form of Cryptococcus in decaying wood and measured the viability of these fungi in environmental samples stored in the laboratory. Samples were collected from a tree known to be positive for Cryptococcus and were each inoculated on 10 Niger seed agar (NSA) plates. The conventional technique (CT) yielded a greater number of positive samples and indicated a higher fungal density [in colony forming units per gram of wood (CFU.g^-1) ] compared to the humid swab technique (ST). However, the difference in positive and false negative results between the CT-ST was not significant. The threshold of detection for the CT was 0.05.10³ CFU.g^-1, while the threshold for the ST was greater than 0.1.10³ CFU^-1. No colonies were recovered using the dry swab technique. We also determined the viability of Cryptococcus in wood samples stored for 45 days at 25ºC using the CT and ST and found that samples not only continued to yield a positive response, but also exhibited an increase in CFU.g^-1, suggesting that Cryptococcus is able to grow in stored environmental samples. The ST.1, in which samples collected with swabs were immediately plated on NSA medium, was more efficient and less laborious than either the CT or ST and required approximately 10 min to perform; however, additional studies are needed to validate this technique.     

Variation of different tree-ring parameters in samples from each terminal shoot of a Norway spruce tree

Variability of wood parameters in a tree is sometimes a rather nebulous concept since variability is evident within single cells, from early to latewood, from pith to bark and from stem base to the top of a tree. So far, stem analyses have been done using a restricted number of parameters, mostly ring-width, and using a restricted number of samples in the longitudinal direction. This study analyses a number of parameters from a single tree. An 81-year-old spruce tree was felled and internodial discs were taken from each annual terminal shoot. All tree rings in each disc were measured and a whole-stem analysis was completed for the following parameters: ring-width, mean ring density, maximum density, percentage of latewood, type of transition from early to latewood, intra-annual density fluctuation, number of resin ducts per tree-ring and position of resin ducts within the tree-rings. All parameters showed calendar-year patterns, visible as lines parallel to the bark. The most clear calendar-year pattern was seen for the type of transition from early to latewood and for intra-annual density fluctuations. The strongest inter-series correlation between calendar rings was seen for ring-width. None of the parameters showed significant inter-series correlations for cambial rings. These results may help us to understand how cores or discs taken at breast height represent the entire tree.     

Elevated atmospheric CO2 alters wood production, wood quality and wood strength of Scots pine (Pinus sylvestris L) after three years of enrichment

Scots pine ( Pinus sylvestris L.) trees were grown in open top chambers for three years under ambient and elevated CO₂ concentrations. The trees were aged 3 y at the beginning of the CO₂ exposure, and the effects of the treatment on total stem volume, stem wood biomass, wood quality and wood anatomy were examined at the end of the exposure. The elevated CO₂ treatment lead to a 49% and 38% increase in stem biomass and stem wood volume, respectively. However, no significant effects of the elevated CO₂ treatment on wood density were observed, neither when green wood density was estimated from stem biomass and stem volume, nor when oven-dry wood density was measured on small wood samples. Under elevated CO₂ significantly wider growth rings were observed. The effect of elevated CO₂ on growth ring width was primarily the result of an increase in earlywood width. Wood compression strength decreased under elevated CO₂ conditions, which could be explained by significantly larger tracheids and the increased earlywood band, that has thinner walls and larger cavities. A significant decrease of the number of resin canals in the third growth ring was observed under the elevated treatment; this might indicate that trees produced and contained less resin, which has implications for disease and pest resistance. So, although wood volume yield in Scots pine increased significantly with elevated CO₂ after three years of treatment, wood density remained unchanged, while wood strength decreased. Whilst wood volume and stem biomass production may increase in this major boreal forest tree species, wood quality and resin production might decrease under future elevated CO₂ conditions.     

A semi-automated method for hexahedral mesh construction of human vertebrae from CT scans

Generation of finite element (FE) meshes of vertebrae from computed tomography (CT) scans is labour intensive due to their geometric complexity. As such, techniques that simplify creation of meshes of vertebrae are needed to make FE analysis feasible for large studies and clinical applications. Techniques to obtain a geometric representation of bone contours from CT scans of vertebrae and construct a hexahedral mesh from the contours were developed. An automated edge detection technique was developed to identify surface contours of the vertebrae, followed by atlas based B-spline curve fitting to construct curves from the edge points. The method was automatic and robust to missing data, with a controllable degree of smoothing and interpolation. Parametric mapping was then used to generate nodes for each CT slice, which were connected between slices to obtain a hexahedral mesh. This method could be adapted for modelling a variety of orthopaedic structures.     

Biomechanical design and long-term stability of trees: Morphological and wood traits involved in the balance between weight increase and the gravitropic reaction

Studies on tree biomechanical design usually focus on stem stiffness, resistance to breakage or uprooting, and elastic stability. Here we consider another biomechanical constraint related to the interaction between growth and gravity. Because stems are slender structures and are never perfectly symmetric, the increase in tree mass always causes bending movements. Given the current mechanical design of trees, integration of these movements over time would ultimately lead to a weeping habit unless some gravitropic correction occurs. This correction is achieved by asymmetric internal forces induced during the maturation of new wood.The long-term stability of a growing stem therefore depends on how the gravitropic correction that is generated by diameter growth balances the disturbance due to increasing self weight. General mechanical formulations based on beam theory are proposed to model these phenomena. The rates of disturbance and correction associated with a growth increment are deduced and expressed as a function of elementary traits of stem morphology, cross-section anatomy and wood properties. Evaluation of these traits using previously published data shows that the balance between the correction and the disturbance strongly depends on the efficiency of the gravitropic correction, which depends on the asymmetry of wood maturation strain, eccentric growth, and gradients in wood stiffness. By combining disturbance and correction rates, the gravitropic performance indicates the dynamics of stem bending during growth. It depends on stem biomechanical traits and dimensions. By analyzing dimensional effects, we show that the necessity for gravitropic correction might constrain stem allometric growth in the long-term. This constraint is compared to the requirement for elastic stability, showing that gravitropic performance limits the increase in height of tilted stem and branches. The performance of this function may thus limit the slenderness and lean of stems, and therefore the ability of the tree to capture light in a heterogeneous environment.     

Radial Gradients in Wood Specific Gravity,Water and Gas Content in Trees of a Mexican Tropical Rain Forest

Cell walls, water, and gas that have mechanical and physiological functions in wood, and wood specific gravity (WSG) is related to demographic traits. To understand variation in wood structure and function, we analyzed radial changes in WSG, in the gas and the water fractions from trees growing in four different habitats in a southern Mexican rain forest. Mean WSG was 0.55 ± 0.16, slightly lower than reported for other tropical forests. In 27 species, WSG decreased and in two species, it increased from pith to bark with a strong (r² = 0.65) negative correlation between WSG in the center of the tree and the radial WSG gradient. Habitat had some effect on mean WSG and trees growing on karst had significantly higher WSG than the same species growing on alluvial soil. The cell wall, water, and gas fractions accounted for 35 percent (range: 16–50), 42 percent (28–65), and 23 percent (2–56), respectively, of wood volume, with a negative correlation between the gas and the cell wall and between the gas and the water fractions, but not between the cell wall and water fractions. Radially increasing WSG is advantageous for pioneer trees with fast initial growth. We found that the water displacement method may result in biased WSG estimates. To increase the accuracy of WSG data, we suggest to measure sample volume geometrically using a constant diameter (that of the borer tip), to include radial variation in WSG, and to consider for possible site effects on species‐specific WSG.     

AutoCellRow (ACR) – A new tool for the automatic quantification of cell radial files in conifer images

Quantitative wood anatomy (QWA) is a growing field of dendrochronology that allows obtaining a large number of parameters as the number, size and spatial arrangement of cellular elements, elements that highlight the adjustments of trees to their environment. In this work, we presented the free/libre open-source software AutoCellRow (ACR), a ready-to-use tool for automatic QWA in conifers. The ACR analyzes radial files of cells on cross-sections views of tree rings and provides automatic measurements of different cell parameters (e.g., lumen radial diameter, double cell wall thickness and cell radial diameter) for each cell along the selected radial file. The ACR measurements are based on high performed image analysis of xylem cells. The accuracy of the software measurements was tested in cross-sections of five conifer species from a semi-arid area of southern Siberia, and compared with measurements obtained by a semiautomatic tool. Our results suggested high accuracy in the ACR cell traits measurements, facilitating and speeding the analysis of quantitative wood anatomy in conifers over radial files of cells.     

中国主要树种木材物理力学属性的地理格局及其环境控制

木材的物理力学属性制约树木生长发育的重要过程,也是决定木材用途的主要依据.研究木材的物理力学属性及其影响因素,可为合理应用木材、科学开展林木选育、改进林业管理等提供必要参考.目前已有的研究多关注单一的木材密度指标,且缺乏多种影响因子的比较.本研究通过建立中国木材物理力学属性及影响因素综合数据库,对自然状态下我国主要树种木材力学属性的分布格局及其驱动因素进行了探讨.结果表明,选择气干密度、弦向干缩系数和冲击韧性作为评估木材物理力学属性的基础指标,比单一木材密度指标更准确,解释率更高;在选用的生活型、气候和土壤等3类因素中,生活型是影响木材力学物理属性变化的最重要因素,气候因子次之,土壤因子基本可忽略,并且气候和土壤因子的作用被生活型所掩盖,这意味着气候因子对于木材物理力学属性的影响是通过影响物种分布而产生作用的.     

Towards automatic quantification of the epicardial fat in non-contrasted CT images

In this work, we present a technique to semi-automatically quantify the epicardial fat in non-contrasted computed tomography (CT) images. The epicardial fat is very close to the pericardial fat, being separated only by the pericardium that appears in the image as a very thin line, which is hard to detect. Therefore, an algorithm that uses the anatomy of the heart was developed to detect the pericardium line via control points of the line. From the points detected an interpolation was applied based on the cubic interpolation, which was also improved to avoid incorrect interpolation that occurs when the two variables are non-monotonic. The method is validated by using a set of 40 CT images of the heart of 40 human subjects. In 62.5% of the cases only minimal user intervention was required and the results compared favourably with the results obtained by the manual process.     

木材上的微生物类群对木材的分解及其演替规律

论述了木材上的微生物类群以及各类群在木材生物分解过程中的演替规律 ,并解释了活立木心材能够发生腐朽的原因。结果表明 :能够生长在木材上的微生物类群有木材腐朽菌、木材软腐菌、木材变色菌、污染性霉菌、细菌、放线菌等多种。这些微生物类群共同合作完成对复杂的木质有机物质的生物分解。它们按一定次序进行作用 ,在木材生物分解的不同时期显示出明显的菌种协调与演替规律。一般情况是细菌、一些半知菌、接合菌和子囊菌等先驱微生物首先侵入 ,然后草本对策的木材腐朽菌开始出现 ,最后由竞争对策或忍耐对策的木腐菌取代草本对策的木腐菌 ,这时木材的分解过程就进入稳定的发展阶段 ,最后使木材分解或腐朽。木材腐朽最终是腐殖化阶段 ,这时微生物群落被土壤习居菌如毛霉、青霉、木霉、镰刀菌及细菌与放线菌等所取代。     

Novel gene expression profiles define the metabolic and physiological processes characteristic of wood and its extractive formation in a hardwood tree species,Robinia pseudoacacia

Wood is of critical importance to humans as a primary feedstock for biofuel, fiber, solid wood products, and various natural compounds including pharmaceuticals. The trunk wood of most tree species has two distinctly different regions: sapwood and heartwood. In addition to the major constituents, wood contains extraneous chemicals that can be removed by extraction with various solvents. The composition and the content of the extractives vary depending on such factors as, species, growth conditions, and time of year when the tree is cut. Despite the great commercial and keen scientific interest, little is known about the tree-specific biology of the formation of heartwood and its extractives. In order to gain insight on the molecular regulations of heartwood and its extractive formation, we carried out global examination of gene expression profiles across the trunk wood of black locust (Robinia pseudoacacia L.) trees. Of the 2,915 expressed sequenced tags (ESTs) that were generated and analyzed in the current study, 55.3% showed no match to known sequences. Cluster analysis of the ESTs identified a total of 2278 unigene sets, which were used to construct cDNA microarrays. Microarray hybridization analyses were then performed to survey the changes in gene expression profiles of trunk wood. The gene expression profiles of wood formation differ according to the region of trunk wood sampled, with highly expressed genes defining the metabolic and physiological processes characteristic of each region. For example, the gene encoding sugar transport had the highest expression in the sapwood, while the structural genes for flavonoid biosynthesis were up-regulated in the sapwood-heartwood transition zone. This analysis also established the expression patterns of 341 previously unknown genes.     

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.     

Spatial patterns of wood traits in China are controlled by phylogeny and the environment

Aim Wood properties are related to tree physiology and mechanical stability and are influenced by both phylogeny and the environment. However, it remains unclear to what extent geographical gradients in wood traits are shaped by either phylogeny or the environment. Here we aimed to disentangle the influences of phylogeny and the environment on spatial trends in wood traits. Location China. Methods We compiled a data set of 11 wood properties for 618 tree species from 98 sampling sites in China to assess their phylogenetic and spatial patterns, and to determine how many of the spatial patterns in wood properties are attributable to the environment after correction for phylogenetic influences. Result All wood traits examined exhibited significant phylogenetic signal. The widest divergence in wood traits was observed between gymnosperms and angiosperms, Rosids and Asterids, Magnoiliids and Eudicots, and in Lamiales. For most wood traits, the majority of trait variation was observed at genus and species levels. The mechanical properties of wood showed correlated evolution with wood density. Most of the mechanical properties of wood exhibited significant latitudinal variation but limited or no altitudinal variation, and were positively correlated with mean annual precipitation based on both Pearson's correlation analysis and the phylogenetic comparative method. Correlations at family level between mean annual temperature and wood density, compression strength, cross‐section hardness, modulus of elasticity and volumetric shrinkage coefficient became significant after correction for phylogenetic influences. Main conclusions Phylogeny interacted with the environment in shaping the spatial patterns of wood traits of trees across China because most wood properties showed strong phylogenetic conservatism and thus affected environmental tolerances and distributions of tree species. Mean annual precipitation was a key environmental factor explaining the spatial patterns of wood traits. Our study provides valuable insights into the geographical patterns in productivity, distribution and ecological strategy of trees linking to wood traits.     

Why are so many trees hollow?

In many living trees, much of the interior of the trunk can be rotten or even hollowed out. Previously, this has been suggested to be adaptive, with microbial or animal consumption of interior wood producing a rain of nutrients to the soil beneath the tree that allows recycling of those nutrients into new growth via the trees roots. Here I propose an alternative (non-exclusive) explanation: such loss of wood comes at very little cost to the tree and so investment in costly chemical defence of this wood is not economic. I discuss how this theory can be tested empirically.