MEASUREMENTS OF RESIDUAL GROWTH STRAINS AT THE STEM SURFACE OBSERVATIONS ON DIFFERENT SPECIES
MEASUREMENTS OF RESIDUAL GROWTH STRAINS AT THE STEM SURFACE OBSERVATIONS ON DIFFERENT SPECIES
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DOI：
10.1051/forest:19940305
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发表时间：
1994-01-01
期刊：
影响因子：
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通讯作者：
GUITARD, D
中科院分区：
文献类型：
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作者：
FOURNIER, M;CHANSON, B;GUITARD, D
直立树木的木材在树木的整个生命周期中都会承受内应力。这种压力通常称为生长压力，源自成熟应变并受到整个树干质量的阻碍。茎表面释放的应变（即通过切槽、钻孔等与茎隔离的一小块木材上的应变）测量成熟应变。我们的“树木结构、解剖学和力学”研究项目旨在 i) 了解成熟应变对树木形态发生（分枝模式、树冠形状、茎和芽相对于垂直方向的位置）的生物控制； ii) 成熟应变与木材的解剖特征和其他木材特性（硬度、收缩率、湿热恢复）之间的合格相关性； iii) 对形成层生长期间连续层的累积成熟所产生的整棵树中的秸秆进行建模和鉴定，以便了解木材加工时的裂缝和应变。本文重点关注在不同物种上测量的茎外围纵向成熟应变的结果。使用了两种方法。 i) 采用中心技术 Forestier Tropical 中设计的特殊传感器的单孔法； ii) 测量由传统电传感器上方和下方锯出的 2 个凹槽引起的应变。两种方法之间的比较表明，在山毛榉和桉树中的一致性相当好，但并不完美，但在栗树中则不然。这些结果从传感器尺寸、方法原理以及木材的解剖和机械特性进行了讨论。对一棵树的测量显示出高度和角度位置的重要变化，这些变化与树的形态发生（树枝的接近度和茎的正确运动）相关。高应变值在树中从来不是均匀的，而是集中在小角扇区。这种成熟应变的角度不对称显然与茎的弯曲运动有关，因为茎的一侧“拉”或“推”另一侧。此外，在松树、桉树无性系（PF1 1.45、UAIC-CTF7、刚果）和杨树（欧洲杨树 cv 1214）、板栗、水青冈和 Eperua falcata 上测量的值的直方图显示菌株分布不是高斯分布。拉伸（在硬木中）或压缩（在软木中）值的长尾与反应木材（压缩或拉伸）的形成相关。种群之间的主要差异不是平均值（在正常标准木材中的尾部），而是尾部的宽度和最大值。因此，为了研究树木种群中生长压力的变异性，我们必须研究树木内高成熟菌株的峰值频率和大小，而不是平均菌株。因此，生长应力应与树木形态的调节相关联，特别是与茎运动动力学（曲率和倾斜的变化）相关联进行分析。最后，在一些热带树木如 Dichostemma sp、Saccoglotis gabonensis、Eperua falcata 和 Castanea sativa 中观察到具有 2 个相对角峰的罕见释放应变模式。这些模式可能与树的结构有关。在丛生树中（即树干由堆叠的树枝构成，因为由腋芽形成的茎从前领导者手中接过），高成熟菌株的峰值似乎是由不同的轴（当前领导者和前领导者）引起的，因此，在横截面中，可以观察到2个高度应变的木材流。这种模式的功能解释并不明显。
The wood in standing trees undergoes internal stress during the entire life of the tree. This stress, commonly named growth stress, originates in maturation strains and is impeded by the mass of the entire trunk. Released strain at the stem surface (ie strain on a small piece of wood isolated from the stem by cutting grooves, drilling holes etc) measures maturation strain. Our research program on 'Tree architecture, anatomy and mechanics' aims at i) understanding the biological control of maturation strain with regard to tree morphogenesis (branching patterns, crown form, stem and shoot positions in relation to vertical direction); ii) qualifying correlations between maturation strain and the anatomical features of the wood and other wood characteristics (stiffness, shrinkage, hygrothermal recovery); iii) modelizing and qualifying the strew in the entire tree that results from the cumulative maturation of successive layers during cambial growth, in order to understand cracks and strains when the wood is processed. This paper focuses on results concerning longitudinal maturation strain at the stem periphery measured on different species. Two methods have been used. i) the single hole method with a special sensor designed in the Centre Technique Forestier Tropical; and ii) measurements of strain due to 2 grooves sawn above and below a classical electric sensor. Comparisons between the 2 methods show quite good, but not perfect, agreements in beech and eucalyptus but not in chesnut. These results are discussed from the sensor dimensions, the principles of the method and the anatomical and mechanical properties of wood. Measurements on one tree show important variations with height and angular position, which are correlated to tree morphogenesis (proximity of branches and righting movements of stems). High strain values are never homogeneous in the tree but concentrated in small angular sectors. This angular asymmetry of maturation strain is obviously related to stem bending movement as one side of the stem 'pulls' or 'pushes' the other. Furthermore, histograms of values measured on Pinus pinaster, clones of Eucalyptus (PF1 1.45, UAIC-CTF7, Congo) and poplar (Populus euramericana cv 1214), Castanea saliva, Fagus sylvatica and Eperua falcata show that the distribution of strains is not Gaussian. The long tail of tensile (in hardwoods) or compressive (in softwood) values correlates with the formation of reaction wood (compression or tension). The main difference between populations is not the mean value (out of the tail, in normal standard wood) but the width and maximum of the tail. Hence, to study variability of growth stress in a population of trees, we must study the frequency and the magnitude of peaks of high maturation strains' within trees, rather than mean strains. Therefore, growth stress should be analyzed in correlation with the regulation of the form of the tree and particularly in correlation with the kinetics of stem movement (changes of curvature and lean). Finally, uncommon patterns of release strain with 2 opposite angular peaks have been observed in some tropical trees as Dichostemma sp, Saccoglotis gabonensis, Eperua falcata and Castanea sativa. These patterns can be related to the tree architecture.In sympodial trees (ie trees in which the trunk is built by stacks of branches as stems formed from axillary buds take over from the former leader), peaks of high maturation strains seem to be induced by the different axes (the present leader and the former) and thus, in a cross-section, 2 flows of highly strained wood can be observed. A functional explanation of such patterns is not obvious.