Patterns of longitudinal and tangential maturation stresses in Eucalyptus nitens plantation trees

Abstract

& Context Tree orientation is controlled by asymmetric mechanical stresses set during wood maturation. The magnitude of maturation stress differs between longitudinal and tangential directions, and between normal and tension woods. & Aims We aimed at evaluating patterns of maturation stress on eucalypt plantation trees and their relation with growth, with a focus on tangential stress evaluation. & Methods Released maturation strains along longitudinal and tangential directions were measured around the circumference of 29 Eucalyptus nitens trees, including both straight and leaning trees. & Results Most trees produced asymmetric patterns of longitudinal maturation strain, but more than half of the maturation strain variability occurred between trees. Many trees produced high longitudinal tensile stress all around their circumference. High longitudinal tensile stress was not systematically associated with the presence of gelatinous layer. The average magnitude of released longitudinal maturation strain was found negatively correlated to the growth rate. A methodology is proposed to ensure reliable evaluation of released maturation strain in both longitudinal and tangential directions. Tangential strain evaluated with this method was lower than previously reported. & Conclusion The stress was always tensile along the longitudinal direction and compressive along the tangential direction, and their respective magnitude was positively correlated. This correlation does not result from a Poisson effect but may be related to the mechanism of maturation stress generation.

Critical review on the mechanisms of maturation stress generation in trees

“…However, recent analyses showed that XG in the G-fibre are not actually located inside the G-layer, but rather at the interface between G-layer and surrounding lignified layers. Finally, this model, as it pulls microfibrils against each other, should result in lateral tensile maturation stress, which is not consistent with observations that tangential maturation stress is compressive and correlated to the magnitude of longitudinal tension [21].…”

“…It is usually estimated using the value of released strain and elastic properties of wood. The magnitude of released strain typically ranges between 20.3% for strong TW and þ0.2% for severe CW [7,21,75,76]. These released strains correspond to a magnitude of stress (far higher than for example turgor pressure, which typically amounts some fractions of MPa) typically ranging between þ50 MPa and 220 MPa, respectively, for TW and CW.…”

Tree growth stress and related problems

“…so that a 0 T can serve as an indicator of r T [33]. The strain-gauge method is useful for rapidly and precisely determining the local strain.…”

“…7). It yields a ''growth stress indicator'' related to the L growth strain by a factor depending on wood anisotropy, characterized by ratios of elastic constants [1,33,34].…”

Growth stresses in old beech poles after thinning: distribution and relation with wood anatomy

“…Trees control the spatial position of their axes (stem or branches) by generation of asymmetrical stress (Fournier et al 1994;Clair et al 2013). Asymmetry of maturation stresses induces a bending moment which maintains (growing branches) or corrects (accidentally tilted stem) the spatial position of axes (Alméras et al 2006).…”