Mechanics of the Compression Wood Response

Archer, Robert R.; Wilson, Brayton F.

doi:10.1104/pp.46.4.550

Cited by 34 publications

(11 citation statements)

References 4 publications

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“…A number of researchers have discussed biomechanical meanings of reaction wood formation, since Archer and Wilson presented a systematic study on the role of abnormal surface growth stress to control the tree shape [18]. A cantilever or curved beam model was used to describe the negative (plagio-) gravitropic behavior of woody plant stems [17,[19][20][21][22][23].…”

Section: Reaction Wood and Biomechanical Control Of A Growing Treementioning

confidence: 99%

Tree growth stress and related problems

et al. 2017

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Tree growth stress, resulted from the combined effects of dead weight increase and cell wall maturation in the growing trees, fulfills biomechanical functions by enhancing the strength of growing stems and by controlling their growth orientation. Its value after new wood formation, named maturation stress, can be determined by measuring the instantaneously released strain at stem periphery. Exceptional levels of longitudinal stress are reached in reaction wood, in the form of compression in gymnosperms or higher-than-usual tension in angiosperms, inspiring theories to explain the generation process of the maturation stress at the level of wood fiber: the synergistic action of compressive stress generated in the amorphous ligninhemicellulose matrix and tensile stress due to the shortening of the crystalline cellulosic framework is a possible driving force. Besides the elastic component, growth stress bears viscoelastic components that are locked in the matured cell wall. Delayed recovery of locked-in components is triggered by increasing temperature under high moisture content: the rheological analysis of this hygrothermal recovery offers the possibility to gain information on the mechanical conditions during wood formation. After tree felling, the presence of residual stress often causes processing defects during logging and lumbering, thus reducing the final yield of harvested resources. In the near future, we expect to develop plantation forests and utilize more wood as industrial resources; in that case, we need to respond to their large growth stress. Thermal treatment is one of the possible countermeasures: green wood heating involves the hygrothermal recovery of viscoelastic locked-in growth strains and tends to counteract the effect of subsequent drying. Methods such as smoke drying of logs are proposed to increase the processing yield at a reasonable cost.

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Section: Reaction Wood and Biomechanical Control Of A Growing Treementioning

confidence: 99%

Tree growth stress and related problems

et al. 2017

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“…This suggests the beam bending equation as a model relating grain weights to shape changes during grain ripening. According to the engineering theory of bending (4), shape (local curvature) is proportional to bending moment K= M/C (1) where K equals curvature, M is the bending moment, and C is a coefficient, the flexural rigidity, which describes the resistance to bending. In a homogeneous beam, the flexural rigidity is the product of E, Young's modulus (the ratio of stress to a longitudinal strain produced by the stress) and I, the moment of inertia of the area about the neutral axis C= Ex I (2) Supported by grants from the California Agricultural Experiment This paper describes the evaluation of the components of equations I and 2 in the rice panicle.…”

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Mechanical Properties of the Rice Panicle

Silk

Wang²,

Cleland³

1982

Plant Physiol.

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Curvature, bending moment, and second moment of stem cross-sectional area were evaluated from photographic data and used to compute flexural rigidity and Young's modulus in the panicle rachis of rice, Oryza sativa L.'M-101.' Flexural rigidity C, and its components E, Young's modulus, and 1, the moment of inertia of the area about the neutral axis, were evaluated 1.5 cm (tip), 9.5 cm (mid), and 16.5 cm (base) from the tip of the panicle rachis. In dynes per square centimeter, C increases from 1.1 x 103 near the tip to 1.09 x 104 in the middle to 5.35 x 104 in the basal region of the rachis. Of the components of C, the I changes have the larger effect, increasing from 2.12 x 10-7 centimeters4 near the tip to 8.21 x 10-7 centimeters' in mid regions to 6.0 x 10-6 centimeters4 in the basal regions. When the rice panicle emerges from its sheathing leaf, it is vertical. As grains fill, the panicle droops so that it is bent in a plane curve with the tip often deflected past the horizontal plane which contains the insertion of the basal branches. Removal of the ripe grains leads to restoration of the vertical orientation. This suggests the beam bending equation as a model relating grain weights to shape changes during grain ripening. According to the engineering theory of bending (4), shape (local curvature) is proportional to bending momentwhere K equals curvature, M is the bending moment, and C is a coefficient, the flexural rigidity, which describes the resistance to bending. In a homogeneous beam, the flexural rigidity is the product of E, Young's modulus (the ratio of stress to a longitudinal strain produced by the stress) and I, the moment of inertia of the area about the neutral axis MATERIALS AND METHODSThe Rice Panicle as a Loaded Beam. Mechanically, the intact rice panicle is a complex structure. Eight to ten branches, each bearing grains, are borne on the rachis (main axis). The branches are wiry and twist to some extent around the stem. Some appear to support the rachis, increasing its rigidity and decreasing local curvature, while others hang below the stem and may act as concentrated loads. To study the mechanical properties of the rachis, the structure was simplified by removing branches with sharp scissors until only the most apical branch remained. Bending moments and curvatures were determined on the singly branched rachis, as described below. Then the branch was removed, and the measurements were repeated on the rachis with its ten grains.The beam model is sketched in Figure 1. Ripening grains act as loads to bend the panicle rachis. A single rice grain attached to the rachis at d produces a bending moment at s, where both d and s are measured from the tip. The bending moment has a direction, which indicates the direction of rotation, and a magnitude, which measures the tendency of the force to make the rigid grain rotate about a fixed axis through s perpendicular to the plane of the curve. The magnitude of the bending moment is the product of the force exerted by the grain and the moment arm ...

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“…The overall result of bending is well known, but the dynamics of the process has been studied only in stems (1,2). Apical control decreases diameter growth in white pine branches (15), but Munch (7) stated that girdles below a branch increased cambial activity without affecting branch movements, suggesting that movement and cambial activity are controlled separately.…”

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Apical Control of Branch Movements in White Pine: Biological Aspects

Wilson¹,

Archer²

1981

Plant Physiol.

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Two-year-old branches on control trees (Pins strobus L.) were compared through a season with branches on trees stem-girdled just above, or below, the branch whorL AU branches first sagged down for 20 days and then moved up for 40 days. Then, control branches reversed and moved back down while branches in both girdle treatments continued to move up. Movement reversal correlated with cessation of both elongation and diameter growth in control branches. Diameter growth continued in branches of girdled trees. Control branches continued to stiffen even after diameter growth stopped. Dffferences in movements due to gdling are from compression wood formed after cessation of branch elongation. Apical control stops cambial activity and compression wood formation in branches after branch elongation ceases, allowing photosynthate produced in the branch to move to the stem. Control branches bend down from increasing selfweight after cambial activity ceases.In white pine (Pinus strobus L.) and most conifers, when the terminal shoot is intact, the lateral branches gradually sag downward over the years. When the terminal shoot is injured or when the stem is girdled above a branch, the uppermost branch bends upward to replace the terminal (4,7,14,15). This bending is from compression wood action in older portions ofthe branch, not from geotropic bending of elongating shoots (16,17). The overall result of bending is well known, but the dynamics of the process has been studied only in stems (1, 2). Apical control decreases diameter growth in white pine branches (15), but Munch (7) stated that girdles below a branch increased cambial activity without affecting branch movements, suggesting that movement and cambial activity are controlled separately. The present paper describes the results of stem girdling experiments to modify apical control of the movements of the 2-year-old portion of 2-year-old branches during their third growing season. We also followed changes in mechanical factors that affect bending and branch movements

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Mechanics of the Compression Wood Response

Cited by 34 publications

References 4 publications

Tree growth stress and related problems

Tree growth stress and related problems

Mechanical Properties of the Rice Panicle

Apical Control of Branch Movements in White Pine: Biological Aspects

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