Larch and white birch growth stresses’ experimental investigation and analysis

In this paper, the equations of tree growth stresses are given by using thick-walled cylinder theory under the assumption that tree trunk is considered as a homogeneous orthogonal anisotropic cylinder. Through a lot of calculation of the experimental data, some figs of growth stresses’ distributions are given, and growth stresses distributions are analyzed.     

On the distribution of tree growth stresses

Summary A plane strain pure bending elastic model is used to predict stress states in a cylindrically orthotropic cylinder due to asymmetric strain distributions continously induced at the periphery. A general solution for the stress states related to each component of the strain distribution expanded in a Fourier series is given. Details of solutions for eleven representative tree species are given. Also the change of curvature of a stem caused by a measured peripheral strain distribution is computed for a given period of growth.     

On the distribution of tree growth stresses

Summary A model for the build up of residual growth stresses in cylindrical tree stems is presented. By using Bessel functions the general equations can be solved to allow for surface strain distributions that vary both in the circumferential as well as longitudinal directions. An arbitrary surface strain distribution can be decomposed into Fourier components and the residual internal stresses can be found by superimposing the component solutions due to each new increment of growth. A numerical simulation leading to the residual stress distribution for a typical hardwood is presented.     

Shrinkage stresses in wood logs considered as layered,cylindrically orthotropic materials

Summary The deformation and stresses in a circular wood log resulting from an arbitrary radial moisture distribution are examined. In this paper the log is modeled as a layered cylinder, with each layer assumed to be linearly elastic, cylindrically orthotropic, and homogeneous. The general solution to the equations of elasticity for a representative layer is given; constants of integration in the solution are determined through application of appropriate continuity conditions at the layer interfaces. Numerical examples are presented for logs of Scots pine which illustrate the effect of nonuniform moisture content upon the displacement and stress distributions.     

阔叶红松林主要树种生长的水热指数和最优生长过程的模拟研究

以阔叶红松林8个主要组成树种为研究对象,根据水分和热量是决定植物地理分布的主要因素的原理,应用干燥度和≥10℃的年积温建立了树木生长水热指数;设在最佳环境条件下树木的生长与叶量成正比,与本身大小成反比,推导出树木最优生长模型。然后,应用该水热指数和生长模型模拟了不同水热条件下树木的最优生长过程,揭示了不同树种、或同一树种在不同水热条件下的生长特征。这些研究结果可用于划分树种地理分布区质量等级和评价林分的生长。     

利用开花结实信息段预测中、幼龄杉木球果产量的研究

林木种子产量预测预报是种子经营工作的重要环节。传统的预测预报方法一般都比较粗放,难以满足当今生产管理的需要,如产量目测法、标准枝法等。近年来有人应用气象学法和灰色动态模型预测法预测林木种子产量,尽管工作量小,技术先进,但由于难以获得可靠的产量历史资料,难以普遍应用。一个好的预测方法必须具备下述三个条件:1.时间超前;2.精度高;3.简便实用。基于这一思路,本文在研究杉木球花及球果在树冠上分布规律的基础上,探讨了利用开花结实信息段预测杉木种子园和一般林分球果产量的方法。     

Finite element study of growth stress formation in wood and related distortion of sawn timber

Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-related stresses (distortions appearing when logs are split up to timber boards by sawing). To get more knowledge on how these distortions can be reduced in wooden products, there is a need for improved understanding of this material behaviour through good numerical tools developed from empirical data. A three-dimensional finite element board distortion model developed by Ormarsson (Doctoral thesis, Publ. 99:7, 1999) has been extended to include the influence of growth stresses by incorporating a one-dimensional finite element growth stress model developed here. The growth stress model is formulated as an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The simulation results presented include how stresses are progressively generated during the tree growth, distortions related to the redistribution of growth stresses during log sawing, and distortions and stresses in drying reflecting the effects of growth stresses. The results show that growth stresses clearly vary during tree growth and also form a large stress gradient from pith to bark. This in itself can result in significant bow and crook deformations when logs are sawn into timber boards. The distortion results from the simulations match well with the results observed in reality. The parametric study also showed that the radial growth stress distribution is highly influenced by parameters such as modulus of elasticity, micro fibril angle and maturation strain.     

Responses of forest trees to single and multiple environmental stresses from seedlings to mature plants: Past stress history,stress interactions,tolerance and acclimation

Forest trees are exposed to a myriad of single and combined stresses with varying strength and duration throughout their lifetime, and many of the simultaneous and successive stress factors strongly interact. While much progress has been achieved in understanding the effects of single stresses on tree performance, multiple interacting stress effects cannot be adequately assessed from combination of single factor analyses. In particular, global change brings about novel combinations of severity and timing of different stresses, the effects of which on tree performance are currently hard to predict. Furthermore, the combinations of stresses commonly sustained by trees change during tree ontogeny. In addition, tree photosynthesis and growth rates decline with increasing tree age and size, while support biomass in roots, stem and branches accumulates and the concentrations of non-structural carbohydrates increase, collectively resulting in an enhancement of non-structural carbon pools. In this review, tree physiological responses to key environmental stress factors and their combinations are analyzed from seedlings to mature trees. The key conclusions of this analysis are that combined stresses can influence survival of large trees even more than chronic exposure to a single predictable stress such as drought. In addition, tree tolerance to many environmental stresses increases throughout the ontogeny as the result of accumulation of non-structural carbon pools, implying major change in sensing, response and acclimation to single and multiple stresses in trees of different size and age.     

Growth stresses and strains in cork

Summary A detailed study of the growth stresses and strains in the cork shell of the cork-oak was undertaken based on experimentally determined constitutive relations for cork in tension and compression. The stresses depend on the thicknesses of the cork shell and of the back layer around the cork shell, on the radius of the trunk and on its increase due to growth. The circumferential stresses in the cork shell and back layer are tensile and increase with increasing distance to the tree axis. The radial stresses are compressive and decrease with increasing distance to the tree axis. The strains due to growth are not recovered when the cork boards are removed, unless the boards are heated, for example, by immersion in boiling water. Other consequences of the growth stresses are analysed, such as the occurrence of corrugations in the lateral cell walls of cork, the variation of width of the successive growth rings and the occurrence of cracks in the back layer and outer cork layers.     

Growth stress distribution in leaning trunks of Cryptomeria japonica

The distribution of growth stresses in leaning trunks of Cryptomeria japonica (L.f.) D. Don was determined by measuring the stresses released by the kerf method with strain gauges glued at specified positions along the trunks. Effects of both tree height and peripheral positions on the surface of leaning trunks on surface growth stress were determined. The inner residual growth strains in leaning trunks were also measured. We found high compression stresses in the lower side of leaning trunks that differed greatly from the tensile stresses in normal erect trunks. However, transverse compression stress was found around the tree trunk in both normal and compression wood. In leaning trees, the distribution of internal stresses in the bent trunk portion differed from that in the erect trunk portion, being compressive on the outside and tensile on the inside. The resistant moment introduced by compression stress generated in compression wood is released by the bending of the leaning trunk. The bending stresses are then superimposed on the original internal growth stress. We demonstrated that Poisson's effect of longitudinal stresses should be considered when evaluating transverse surface growth stresses. The existence and intensity of compression wood development can be assessed by growth stress measurements. We conclude that the compressing force of compression wood functions physiologically to give an upward righting response in a leaning trunk.     

平远县古树资源调查初报

对平远县的古树进行了多次调查,结果表明,该县百年以上古树资源较为丰富,到2003年为止, 已知有1 646株,分布于全县12个镇,大多数植株生长较好,也有少部分植株濒临死亡或已经死亡。文章还根据古树资源的现状及存在问题,提出了有效的管理和保护措施。     

On the distribution of tree growth stresses

Summary A plane strain pure bending model is used to predict stress states in a transversely isotropic cylinder due to asymmetric strain distributions continuously induced at the periphery. A general solution for the stress states related to each component of the strain distribution expanded in a Fourier series is given. An expression for the change of curvature due to each new growth increment is derived.This work was supported in part by NSF Grant ENG 74-02428.     

Three-dimensional reconstruction of stems for assessment of taper,sweep and lean based on laser scanning of standing trees

A method and algorithm for reconstructing the three-dimensional (3D) surface of stems based on terrestrial laser scanner data from standing trees is presented. Laser scanning delivers a dense cloud of points, and this raw point data are filtered for deriving a digital terrain model and subsequent fitting of a parametric stem model. The stem model is made up of a sequence of successive cylinders that overlap in space; each cylinder is parameterized by its orientation and radius. The model is estimated iteratively from a given starting point and by adding cylinder segments. Successive segments are added whenever criteria on deviation in orientation and radius relative to the previous cylinder and a fit statistic to the point data are met. The method has proven applicable when applied to a European beech tree and a wild cherry tree from dense forest stands. The use of the resulting 3D reconstruction of tree stems in respect to diameter in breast height and height of crown base calculation, as well as taper, sweep and lean assessment of standing trees, is described. Finally, desirable future improvements to the basic algorithm are discussed.     

闽南福建柏人工林生长动态的研究

通过对１９６０～１９９５ 年间营造的福建柏人工纯林的调查, 对福建柏的胸径、树高、材积、形数和树干生长规律进行分析, 分别建立生长过程模型。结果表明, 福建柏树高速生期比胸径早, 幼龄阶段材积增长缓慢,１２ａ 后材积生长加速; 随树龄的增大, 胸径形数呈反向生长, 树形不断向圆锥体靠近。     

Tree growth as indicator of tree vitality and of tree reaction to environmental stress: a review

The intensive monitoring plots (Level II) of ICP Forests serve to examine the effects of air pollution and other stress factors on forest condition, including tree vitality. However, tree vitality cannot be measured directly. Indicators, such as tree growth or crown transparency, may instead be used. Tree growth processes can be ranked by order of importance in foliage growth, root growth, bud growth, storage tissue growth, stem growth, growth of defence compounds and reproductive growth. Under stress photosynthesis is reduced and carbon allocation is altered. Stem growth may be reduced early on as it is not directly vital to the tree. Actual growth must be compared against a reference growth, such as the growth of trees without the presumed stress, the growth of presumed healthy trees, the growth in a presumed stress-free period or the expected growth derived from models. Several examples from intensive monitoring plots in Switzerland illustrate how tree-growth reactions to environmental stresses may serve as vitality indicator. Crown transparency and growth can complement each other. For example, defoliation by insects becomes first visible in crown transparency while stem growth reaction occurs with delay. On the other hand, extreme summer drought as observed in large parts of Europe in 2003 affects stem growth almost immediately, while foliage reduction becomes only visible months later. Residuals of tree growth models may also serve as indicators of changed environmental conditions. Certain stresses, such as drought or insect defoliation cause immediate reactions and are not detectable in five-year growth intervals. Therefore, annual or inter-annual stem growth should be assessed in long-term monitoring plots. An erratum to this article can be found at     

On the distribution of tree growth stresses

Summary Growth stress distributions in trees are derived using the hypothesis that longitudinal and circumferential growth strains are continuously induced at the periphery of the growing stem. A plane strain combined with pure torsion model is used to compute the internal stresses and strains due to forces and moments caused by the new growth increment. The twisting angle of the pure torsion model is caused by the shear stresses set up in the growth increment as the growth strains are induced along the grain axis and the coupling of axial and torsional effects due to the elastic constants for the inclined grain material. Detailed stress distributions are derived for a range of constant grain angle cases. The extreme sensitivity of the torsional shear distribution to small grain angles is noteworthy.This work was supported in part by NSF Grant ENG 74-02428     

Forest shadows: How much shelter in a shelterwood?

A simulation model is presented that will permit silviculturists to estimate the shade cast on any site at any time by a randomly distributed conifer stand of any stocking level. Computational requirements are modest. Simple situations may be solved in an hour or so on a programmable hand calculator; most complex situations can be handled on a desk microcomputer.Trees are modelled as a crown consisting of a cone on top of a cylinder, and the crowns may vary in density. The bole is modelled as a solid cylinder. Relative dimensions may be varied to simulate almost all regular conifer tree forms. The projected shadow area of trees is integrated for any number od independently distributed trees to obtain the relative shadow area on the ground surface. Alternatively, the model permits the determination of the number of trees of any given dimensions per unit are needed to provide a given degree of shade.     

马尾松幼苗年生长规律研究初报

对马尾松幼苗年生长规律研究结果表明，苗高和地径生长进程有差异，影响苗高，地径生长的气象因子也不同。作者在生长规律研究的基础上，对低山丘陵马尾松的造林管理提出了建议。     

Generation of radial growth stresses in the big rays of konara oak trees

 In previous models the distribution of radial tensile stresses in the tree trunk has been explained as a response to the mechanisms of growth stress generation in the longitudinal and tangential directions. We investigated the contribution of ray tissue to growth stress generation in the tree trunk by the origin of the radial stresses during differentiation of parenchyma cells. Measurements on three konara oak trees (Quercus serrata Thunb.) were carried out comparing the radial residual strain of big oak rays with the radial residual strain of the axial tissues (containing only uniseriate rays). The results indicated that the ray tissue generated tensile growth stress in the radial direction of the trunk (the axial direction of the parenchyma cells). In contrast to previous assumptions, the growth stresses seem to be variable in relation to the individual tissue types. The mechanical advantage of a radially prestraining effect of the rays is discussed for the living tree. Received: October 9, 2001 / Accepted: April 22, 2002 Acknowledgments This research was carried out during a 2-month short-term stay of the first author at Nagoya University. The financial and organizational support by Monbusho Foundation is gratefully acknowledged. Correspondence to:I. Burgert     

广德县古树树势与健康状况评价

在全面普查和专项补充调查的基础上,基于树形与生长方面的9个量化指标对安徽省广德县古树树势与健康状况进行综合评价。结果认为,全县古树总体上树势一般,呈中等健康水平,但不同的树种差别较大,其中生长缓慢的大乔木树种,凡处于中年阶段的古树,大多树势生长旺盛,健康等级高;乡土树种古树适应当地自然条件的能力较强,生长较好,健康等级较高;而速生树种或引入归化树种的古树,在处于生长的末期阶段,一般长势不佳,健康等级较低;具有量多面广的同一古树,树势旺盛,健康等级较高。不同保护级别的古树,树势和健康等级也各有差异,总的趋势是保护级别越高,树势越差,健康等级越低。生理老化、自然灾害、环境恶化、病虫危害、管护不善等则是当前影响古树树势和健康的主要因素。