Modelling the growth stress in tree branches: eccentric growth vs. reaction wood

Abstract

9 This work aims to model the mechanical processes used by tree branches to control their posture despite 10 their increasing weight loading. The two known options for a branch to maintain its orientation are the 11 asymmetry of maturation stress, including reaction wood formation, and eccentric radial growth. Both 12 options can be observed in nature and influence the stress distribution developed in the branch each 13 year. This so-called "growth stress" reflects the mechanical state of the branch. In this work, a growth 14 stress model was developed at the cross-section level in order to quantify and study the bio-mechanical 15 impact of each process. For illustration, this model was applied to branches of two 50-year-old trees, 16 one softwood Pinus pinaster and one hardwood Prunus avium (wild cherry tree), both simulated with 17 the AmapSim discrete element software. For the wild cherry tree, the computed ouputs enlightened that 18 the eccentricity of radial growth seems to be as efficient as the formation of reaction wood to maintain 19 the postural control despite the increasing gravity. err The computed outputs enlightened that, for both 20 Prunus avium and Pinus pinaster , eccentric radial growth appears less efficient than the formation of 21 reaction wood to counter the increasing gravity stress applied to the branch. err For the pine tree, eccentric 22 radial growth appears to be less efficient than the formation of reaction wood err . But although eccentric 23 growth err it err does not necessarily act as a relevant lever for postural control, it greatly modifies the