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Mechanical properties of “flexure wood”: compressive stresses in living trees improve the mechanical resilience of wood and its resistance to damage


Key message

Mechanical acclimation of young poplars ( Populus tremula × Populus alba , INRA 717-1B4) submitted to periodic stem bending is mainly driven by compressive strains. Flexure wood and compressive flexure wood exhibit higher mechanical resilience and lower mechanical damage.


It is well known that thigmomorphogenesis modulates tree growth and the anatomical structure of wood. However, nothing is known about the mechanical behaviour of the tissues of fresh wood formed under mechanical stimulation.


We investigated the elastic and plastic properties of the fresh wood of young poplar trees (Populus tremula × Populus alba, INRA 717-1B4) submitted to periodic controlled stem bending that mimics the mechanical effect of wind.


For a set of trees, we applied symmetrical bending treatments, which led to the formation of “flexure wood”. For another set of trees, asymmetrical bending treatments, including compression (or tension) only, were applied and generated specific wood formation: “compressive flexure wood” and “tensile flexure wood”. We investigated the elastic and plastic properties of these woods at the stem and at the local tissue levels.


The results revealed that fresh wood formed under compressive treatments is more resistant to damage (damage reduced by 44%) and a higher mechanical resilience (+ 33%), suggesting that this tissue is able to withstand higher mechanical strains than “normal wood”. This improvement could explain the higher mechanical strength of the stem to bending (+ 42%).


When trees experience repetitive mechanical stimulations, they adjust the plastic plastic behaviour of their wood in a way that improves the mechanical safety. This demonstrates the adaptive benefit of the mechanical acclimation of trees.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.



Control trees


Trees experiencing asymmetrical mechanical stimulations


Trees experiencing symmetrical mechanical stimulations


Normal wood: it is formed in the control trees, i.e. without any mechanical stimulations


Compressive flexure wood: it is formed under repeated compressive strain in MSa trees


Tensile flexure wood: it is formed under repeated tensile strain in MSa trees


Flexure wood: it is formed alternatively under repeated tensile and compressive strain in MSs trees


Neutral wood formed in the neutral line of MSa trees during the asymmetrical stem bending treatment


Neutral wood formed in the neutral line of MSs trees during the asymmetrical stem bending treatment


Neutral wood gathering MSa-N and MSs-N: it refers to the wood tissues in the neutral line during the asymmetrical (MSa-N) and symmetrical (MSs-N) stem bending treatment


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The authors thank Christelle Boisselet, Patrice Chaleil, Pierre Conchon, Aline Faure, Brigitte Girard, Stéphane Ploquin and Romain Souchal (UMR UCA-INRAE PIAF) for their technical support and the SILVATECH platform for MFA measurements.


This work was supported by grants from the Auvergne-Rhônes-Alpes Regional Council and EFPA department of National Institute for Agronomic Research (INRAE).

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Correspondence to Eric Badel.

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Contributions of the co-authors

EB, JD and BM conceived the study. BN performed the experiments, data collection and laboratory work. JR performed the MFA measurements. BN initially summarized and analysed the data and wrote the initial draft. BN, JD, JG, JR, ET, BM and EB contributed to the writing of the final draft.

Handling Editor: Jean-Michel Leban



Table 3 Number of tested samples. C refers to control trees. MSa and MSs refer to stems that experienced asymmetrical and symmetrical bending treatments, respectively. NW represents the “normal wood” (no-bending stimulation), CFW (resp. TFW) refers to wood tissues that experienced compressive (resp. tensile) strain only during the stem bending treatment. MSa-N and MSs-N refer to wood tissues in the neutral line during the asymmetrical (resp. symmetrical) stem bending treatment. FW (flexure wood) refers to wood tissues that alternatively experienced tension and compression strain (symmetrical bending treatment). MOR stands for the modulus of rupture
Fig. 10

Experimental dampened sinusoidal signal from the incremental angular position sensor. αinitial stands for the initial position of the pendulum and αfinal is the final position of the pendulum after the breakage of the millimetric beam. The difference between these two positions, Δα, corresponds to the difference of potential energy that matches the total energy dissipated during the test, ΔE

Fig. 11

Micro-bending test monitored by camera (.gif). Black marks have been drawn on the sample in order to monitor the displacement of the sample without contact. The movie depicts the three preliminary loading cycles, the loading cycle to 0.8% of strain and, finally, the last loading until rupture

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Niez, B., Dlouha, J., Gril, J. et al. Mechanical properties of “flexure wood”: compressive stresses in living trees improve the mechanical resilience of wood and its resistance to damage. Annals of Forest Science 77, 17 (2020). https://doi.org/10.1007/s13595-020-0926-8

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  • Mechanical stress
  • Thigmomorphogenesis
  • Fresh wood
  • Mechanical behaviour