Growth Stresses and Strains in Trees

Archer, Robert R.

doi:10.1007/978-3-662-02511-6

Cited by 176 publications

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“…A less visible but equally important condition is the prestressing resulting from the cellular maturation, which not only improves the strength of the stem but also controls its orientation through the asymmetry of growth and stress distribution. 1,2 In the case of strong reorientation requirements, a so-called reaction wood is produced, characterized by distinctive anatomical features and biomechanical action. In softwoods the lower part of a leaning stem would produce a tissue that tends to expand during maturation and is thus subject to compression stress.…”

Section: Introductionmentioning

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Characterization of a Gel in the Cell Wall To Elucidate the Paradoxical Shrinkage of Tension Wood

et al. 2007

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Wood behavior is characterized by high sensibility to humidity and strongly anisotropic properties. The drying shrinkage along the fibers, usually small due to the reinforcing action of cellulosic microfibrils, is surprisingly high in the so-called tension wood, produced by trees to respond to strong reorientation requirements. In this study, nitrogen adsorption-desorption isotherms of supercritically dried tension wood and normal wood show that the tension wood cell wall has a gel-like structure characterized by a pore surface more than 30 times higher than that in normal wood. Syneresis of the tension wood gel explains its paradoxical drying shrinkage. This result could help to reduce technological problems during drying. Potential applications in biomechanics and biomimetics are worth investigating, considering that, in living trees, tension wood produces tensile growth stresses 10 times higher than that of normal wood.

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Section: Introductionmentioning

confidence: 99%

Characterization of a Gel in the Cell Wall To Elucidate the Paradoxical Shrinkage of Tension Wood

et al. 2007

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“…), maturation strains involve shrinkage in the longitudinal and radial directions, and swelling in the tangential direction (Archer, 1986). Maturation strains in the longitudinal direction are about 10 times higher than in the other directions (Archer, 1986). Tree axes are generally slender structures and can be considered as beams.…”

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“…It has been be observed that the measured residual longitudinal maturation strains (rlms) underestimate the original maturation strain for two reasons: (1) The piece of wood on which shrinkage is measured is not completely disconnected from the rest of the trunk (Coutand et al, 2004); (2) green wood is known to be a viscoelastic material so that the release of some of the initial strains is delayed and can only be released after a long time or after an accelerating hygrothermal treatment (Gril and Thibaut, 1994). Maturation strains are generally higher (in absolute values) in reaction wood than in opposite or normal wood so that any asymmetric production of reaction wood induces a reorientation of the stem (Archer, 1986).…”

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“…Sinnott, 1952;Archer and Wilson, 1973;Yoshisawa and Okamoto, 1986;Wilson and Gartner, 1996). Moreover, quantification and mechanical analyses of the tropic movement of lignified axes over time have been little considered (except for a few studies on conifers; Archer andWilson 1973, 1982;Fournier et al, 1994). On young organs displaying primary growth, the gravitropic response consists of an upward curving response followed by a decurving phase, enabling the axis to avoid overshooting the vertical.…”

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The Gravitropic Response of Poplar Trunks: Key Roles of Prestressed Wood Regulation and the Relative Kinetics of Cambial Growth versus Wood Maturation

2007

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In tree trunks, the motor of gravitropism involves radial growth and differentiation of reaction wood (Archer, 1986). The first aim of this study was to quantify the kinematics of gravitropic response in young poplar (Populus nigra x Populus deltoides, 'I4551') by measuring the kinematics of curvature fields along trunks. Three phases were identified, including latency, upward curving, and an anticipative autotropic decurving, which has been overlooked in research on trees. The biological and mechanical bases of these processes were investigated by assessing the biomechanical model of Fournier et al. (1994). Its application at two different time spans of integration made it possible to test hypotheses on maturation, separating the effects of radial growth and cross section size from those of wood prestressing. A significant correlation between trunk curvature and Fournier's model integrated over the growing season was found, but only explained 32% of the total variance. Moreover, over a week's time period, the model failed due to a clear out phasing of the kinetics of radial growth and curvature that the model does not take into account. This demonstrates a key role of the relative kinetics of radial growth and the maturation process during gravitropism. Moreover, the degree of maturation strains appears to differ in the tension woods produced during the upward curving and decurving phases. Cell wall maturation seems to be regulated to achieve control over the degree of prestressing of tension wood, providing effective control of trunk shape.

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Do tall tree species have higher relative stiffness than shorter species?

Jagels

Equiza

Maguire

et al. 2018

American J of Botany

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Premise of the StudyIn 1757 Leonhard Euler demonstrated that to avoid bending tall columns needed to be stiffer but not stronger than shorter columns of equal diameter and material density. Many researchers have concluded that trees have a fixed stiffness to basic density ratio, and therefore, trees adjust for increasing height by adding mass to adjust stem form. But the wood science literature points to considerable variance in stiffness with respect to green wood density.MethodsUsing the vast global repository of green wood mechanical properties, we compared relative stiffness and relative strength between taller and shorter species. For North American trees, we examined stem moisture distribution.Key ResultsFor all regions of the world, taller species on average possessed greater stiffness, but not strength, than shorter species of equal basic specific gravity. We looked for a possible universal mechanism that might allow taller tree species to adjust stiffness without affecting xylem specific gravity and concluded that the evidence points to a decrease in cellulose microfibril angle in structural cell walls combined with possible increases in holocellulose percentage. The evidence is strongest for conifers. We also showed that tall conifers have the ability to adjust the distribution of xylem moisture to maximize conduction while minimizing column load.ConclusionsOur research reveals that taller trees have developed internal stem adjustments to minimize diameter increase while attaining ever‐greater heights, thus enabling these taller species to reduce energy expended on biomass accumulation while gaining greater access to solar radiation.

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Growth Stresses and Strains in Trees

Cited by 176 publications

References 0 publications

Characterization of a Gel in the Cell Wall To Elucidate the Paradoxical Shrinkage of Tension Wood

Characterization of a Gel in the Cell Wall To Elucidate the Paradoxical Shrinkage of Tension Wood

The Gravitropic Response of Poplar Trunks: Key Roles of Prestressed Wood Regulation and the Relative Kinetics of Cambial Growth versus Wood Maturation

Do tall tree species have higher relative stiffness than shorter species?

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