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.     

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     

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.     

On the origin of growth stresses in trees

Summary A mechanism for growth stress generation is studied which involves a contractive strain in the microfibril direction and swelling strain in the transverse direction in the developing wall of wood cells. A cylindrically anisotropic elastic model is used to calculate the accumulation of residual stresses in the S₂ wall as it is formed. An explicit relation between the shrinkage/swelling strains in the growth increment of the cell wall and the resulting axial and circumferential stresses induced in the cell is derived. For gymnosperm cells the transition from tensile stress in normal wood cells to compressive stress in compression wood cells is found with increasing microfibril angle.     

On the origin of growth stresses in trees

Summary The mechanics of growth stress generation in a tissue of developing wood cells is studied by means of a continuum-mechanical model which assumes that the stresses which accumulate in the cells are induced by growth strains in the newly formed cell wall increments as they are laid down. The feasibility of the model is examined by using cell parameters both anatomical and physical to predict the variation of growth stresses with microfibril angle. In particular the measured change from tensile to compressive stresses with increasing microfibril angle for conifers is compared with the results predicted by the model.     

银杏发展前景有多远

随着银杏种植业的发展 ,各种银杏加工企业迅速崛起 ,形成一个有强大生命力的银杏产业。８０年代以来 ,全国不少地区把发展银杏当作调整产业结构 ,作为振兴地方经济的支柱产业和振兴农村经济的战略工程来抓 ,大搞银杏肓苗 ,经销果、叶、苗及加工产品 ,既促进了银杏生产的发展 ,又获得了丰厚的效益。近年来 ,我国有关部门大面积繁殖银杏苗木 ,有些地方出现了卖苗难和卖叶难的问题 ,出现低价倾销优良接穗的现象 ,每个优良接穗芽由原来的０.５元跌至０ .１０～０.０５元。有的厂家低价倾销银杏叶提取物ＧＢＥ ,每公斤１５００元左右。这些现象和…     

Primordium initiation drives tree growth

Key message

Tree growth is driven by leaf primordium initiation at shoot apices through a series of growth and developmental events largely mediated hormonally and often determinate in nature. This repeating pattern keeps trees alive and reproductive and conserves the phenotype.

     

红松不同分布亚区优树群体结实与生长性状分析

对露水河红松无性系种子园中不同分布亚区优树群体的结实和生长性状进行调查与分析,结果表明：在相同立地条件下,结实株率、种子平均产量以南亚区优树群体最高,其次为北亚区,中亚区最低;单株平均结实数、球果平均长度与宽度、单果平均重量、千粒重以南亚区优树最高,其次为中亚区,北亚区最低,与纬度呈现反比状态,而与温度和湿度呈正比。南亚区优树群体的平均树高生长量最大,为10.2 m,分别高出北亚区、中亚区及对照的29.11%、59.38%、92.82%。胸径平均生长量各分布亚区的优树群体之间差异不显著,但均分别高出对照24.87%、21.64%、18.41%。     

Use of modeled photosynthesis and decomposition to describe tree growth at the northern tree line

Growth of subarctic Scots pine (Pinus sylvestris L.) trees was investigated by a combination of process-based models and dendroecological approaches. Tree ring width indices were strongly autocorrelated and correlated with simulated photosynthetic production of the previous year and with organic matter N mineralization of the current year. An autoregressive model, with photosynthesis and N mineralization as external inputs, explained growth of the trees well. However, relationships for the period 1950-1992 differed significantly from relationships for the period 1876-1949; the slope of the regression of tree ring width index and photosynthesis was lower for the 1950-1992 period. Also, the autocorrelation structure of the data changed. First-order autocorrelation decreased and second-order autocorrelation increased from the earlier to the later period. This means that growth is becoming less sensitive to variations in photosynthetic production, whereas the relationships between growth and N mineralization are remaining fairly constant. We postulate that, although photosynthesis has increased in response to increasing CO2 concentrations, tree growth rate cannot parallel the increase in photosynthesis because potential growth rate is limited directly by temperature.     

浅谈林木种子包装

商品的生产就是为了销售,要销售商品就要让消费者了解商品并有责任保护好商品。包装是商品的一个组成部分。在商品经营大潮中,包装一直随着商品社会的发展而发展。现在几乎所有商品都有美丽而方便的包装。包装已经充满了整个商品世界。随着林业事业的飞速发展,林木种子也已     

浅淡林木种子园的规划设计问题

根据生产实践的要求 ,阐明了种子园的建立方法与步骤 ,技术要点 ,注意事项     

An elastic,plastic theory of longitudinal growth stresses

Summary The problem of predicting the distribution of longitudinal growth stresses in a symmetrical, standing, woody stem is treated. It is assumed that coupling effects between longitudinal and transverse stress components are negligible so that the longitudinal stress distribution can be determined independently. One novel feature introduced in this analysis is that the material behaviour is assummed to be elastic, plastic rather than wholly elastic as in previous analyses of this problem. This assumption successfully limits the maximum intensity of the longitudinal compressive stress near the center of the stem. Another novel feature of the present analysis is that the initial, longitudinal, tensile stress at the periphery of the stem varies inversely with the size of the stem rather than being assumed constant as in previous analyses. Results obtained from this analysis are compared with previously published experimental data for curvatures and length changes of strips cut from diametral planks. The agreement is very good with the length change data over a wide range of stem sizes.     

不同坡位对油茶生产力的影响

良种在阳坡及阴坡的不同坡位下其生产力不同,种在阳坡下部生产力最高,中部次之,上部最小;在阴坡以中部生产力最高,下部次之,上部最小。由同一立地条件良种与非良种生产力方差分析表明:阳坡中下部及阴坡中下部由于水肥条件较好,良种的生产力比非良种的大,二者差异达到显著水平。由不同立地条件油茶单位产量数量化得分表可知,良种与否、坡位、坡向分别是影响油茶产量的第一、第二、第三重要因子。     

19种木兰科树种早期生长比较

该文对中山市树木园木兰园中其中19种木兰科树种的早期生长进行了比较研究。结果表明:合果木和灰木莲生长速度最快;鹅掌楸、亮叶含笑、灰绒含笑生长较快;观光木、云南拟单性木兰、乐昌含笑、大叶木莲、火力楠、白玉兰、黄兰、海南木莲、乐东拟单性木兰、苦梓含笑、阔瓣含笑生长中等,其他生长较慢。     

盐碱地林木生长规律的研究

该项研究 ,旨在摸清刺槐、榆树、八里庄杨、新疆杨、毛白杨等几个树种 ,在土壤含盐量不同的条件下 ,其高、径、材积的生长变化规律 ,从中筛选优势树种 ,为制定盐碱地区的林业生产方案和措施 ,提供可靠依据     

植物生长调节剂对林木生长的控制

用植物生长调节剂处理樟子松。丁香幼苗。实验表明,经处理后的幼苗。高径生长提高１５％￣３０％。樟子松小苗造林成活率平均提高１９．８７％。     

康氏粉蚧卵囊在梨树上的空间分布研究

对康氏粉蚧Pseudococcus comstocki(Kuwana)卵囊在梨树上的空间分布研究表明,越冬卵囊在京白梨Pyrus ussuriensis var.ovoidea上的总体分布顺序是主枝主干侧枝中心干,在树干上的分布是南部东部西部北部,在不同朝向主枝上的分布是南部东部北部西部,在主枝和侧枝下部的数量明显多于上部,卵囊总数与粗皮面积呈极显著的正相关,二者之间的Person相关系数(R)达到0.964(P=0.000)。调查结果为康氏粉蚧的物理防治提供了理论依据。     

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     

浅谈林木抗旱性评价方法

树种抗旱性的评价对旱区造林树种的选择与良种繁育有重要的指导作用。本文在综合树木抗旱性研究的基础上 ,指出评价抗旱性的形态指标、生理指标和生产力指标 ,并提出多树种抗旱性评价的数学方法