Diversity of bark contribution to mechanical function of trees


2017- 2019
This project is bilaterally supported by CEBA (Centre of Studies on Biodiversity in Amazonia) and NumEV (Montpellier’s Labex at the interface between physical/numerical sciences and life/environmental sciences).


Tancrède ALMERAS ( LMGC, Montpellier)
Pour EcoFoG: Bruno Clair

Scientific Partnership

  • LMGC - Montpellier, France

Presentation of the project

The mechanical functions of the tree include stiffness, necessary to maintain elastic stability, and a motor function, necessary to control tree posture, i.e. maintain and adapt the orientation of its axes during growth. The role of wood for these functions, and its diversity across species, is well-documented. Recently, we identified species for which bark rather than wood has a major role in the motor function. This raises the issues of the mechanism underlying the efficiency in this function, its possible change with tree size and its diversity across species.
This project aims at: identifying the diversity of mechanisms involved in the motor function of bark, including new mechanisms to be discovered; quantifying the contributions of bark vs. wood to the tree posture control, along a gradient in stem size within species and among a diversity of tropical tree species.
The project is structured into 3 tasks: (1) Understanding the mechanisms enabling the motor function of bark, (2) Ontogeny and scaling effect on bark contribution to trunk and branch biomechanics, (3) Diversity of posture control strategies.
Task 1 will be conducted on 6 models species already identified as having diverse strategies for posture control. Saplings grown in greenhouse and adult trees in the forest will be used for this study. Besides a basic set of measurements (bark thickness, bark and wood density, anatomical observations), specific mechanical measurement (change in curvature during the removal of bark, released strains on living trees, elastic properties of bark) will be performed to clarify the mechanism. A mechanical model will be developed to assess quantitatively the hypothetic mechanisms that induce mechanical stress in bark.
Task 2 will be restricted to a couple of species, for which the sampling will cover a large range of stem diameters. The same basic set of measurements as in task 1 will be performed to analyse the changes in bark properties and structure with size, enabling the mechanical assessment of changes in bark efficiency with size.
Task 3 will be conducted on a large diversity of angiosperm tropical tree species, with limited number of replicates per species. The same basic set of measurements as in task 1 will be performed on naturally tilted stems or branches. This will enable the identification of species posture control strategies and the study of their structuration within a phylogeny. Relation between strategies and easy-to-measure traits (bark thickness and density) should enable the definition of new traits to be taken into account in future large-scale ecological studies.

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