Conclusion

Previous studies in biomechanics should be considered when defining tree traits to be used to describe the mechanical aspects of height growth strategy. It is assumed that this strategy presents a competitive challenge with regards to physical constraints, especially in forest canopies where light is limited in the understory and increases with canopy height. Two growth processes have been suggested to play a major role in these strategies. The first is thigmomorphogenesis, i.e., the perception of mechanical loads and the plant growth response, which influences biomass allocation between roots and shoots, organ length and thickness, as well as stem and root system shape and their wood properties. The second is concerned with long-term gravitropic movements of lignified and stiff stems induced by secondary growth and maturation strains, which are continuously being generated to maintain verticality.

Studying the biomechanical aspect of a species' strategy is of general interest for forest ecologists for different reasons. Firstly, biomechanics can contribute to a better understanding of the relationships between diversity and functioning. For example, with regards to the ability of trees to coexist at different height strata, both competition and physical constraints can be interpreted as the use of different ecological niches with respect to light availability, which in turn could influence general ecosystem functioning and productivity. Biomechanics could therefore be useful for studying the relationships between tree functional types and natural ecosystem resilience or community dynamics. The efficiency of certain pioneer shade-intolerant species, which tend to dominate in gaps of disturbed forests and are able to survive under a closed canopy before becoming canopy trees in mature forests, should be linked to their ability to use support material at a low cost with a high mechanical efficiency, thus decreasing the risk of failure. Lastly, biomechanics can give valuable help when assessing species performance in engineering, such as stabilizing the soil on slopes through the use of vegetation or the choice of sylvi-cultural practices in a windy environment.

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