Tree growth stress and related problems

Abstract

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.

Effect of growth stress and interlocked grain on splitting of seven different hybrid clones ofEucalyptus grandis×Eucalyptus urophyllawood

“…Growth stress is a result of tree growth and it is formed by a combination of the formation of a new wood layer during the differentiation process and the weight accumulated in the trunks of trees (Archer 1986;Fournier et al 1994). Growth stresses are a biomechanical function that reorient the trees to a better position (Kubler 1987;Mattheck and Kubler 1995), are essential for tree survival (Gril et al 2017), and the distribution of growth stresses around the stem circumference may be asymmetric (Jullien et al 2013). Growth stresses have a direct influence on the development of crooking and splitting immediately after harvesting (Okuyama et al 1981;Hillis 1984;Purnell 1988;Tejada et al 1997;Yang et al 2001).…”

ELIMÄKI locus is required for mechanosensing and proprioception in birch trees

“…Here, the weight vertically loads on the stem column in parallel to the gravity vector. Simultaneously, the radial growth increases compressive forces in the wood forming zone, and accumulates tensile stress at the periphery (14). While some of these forces have been measured by interpreting the residual stress (30), the extent to which this mechanical conflicts surrounding the cambium can conditionate wood formation remains hypothetical.…”

“…Moreover, the mechanical pressure in the VC may be required for xylem differentiation in trees (13). This suggest that the VC responds to mechanical stimulus by integrating multi-scale signals derived from vertical loading and radial growth (maturation stress) (14). Interestingly, the direct response of tree stems to a vertical static loading on was not tested before.…”

Study on the changes in surface characteristics of Populus tomentosa due to thermo-hydro-process

“…Poplar wood used in this study is a fast-growing wood which results in higher growth stresses. Thermal treatment was reported as one of the possible countermeasures to reduce growth stresses in wood [14]. Hence, the specimens were first oven-dried in the purpose of releasing the growth stress in certain extent, which consequently minimize the effects of specimens' variation on the test results and then were vacuum treated, so that all the specimens were fully water-saturated with a similar moisture content.…”