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Etude des stratégies biomécaniques de croissance des jeunes arbres en peuplement hétérogène tropical humide

Abstract : The functioning of ecosystems is based on the functional diversity, which is the complement to the species diversity. In the tropical rain forest, the saplings grow in the dense and stratified understorey. This thesis deals with the diversity of realisation of the support function by the saplings in this context. The hypotheses are that the race through higher and so brighter levels constrains the mechanical security of the saplings with necessary biomass saving and need of reorientation (gravitropism) and acclimation (mecanoperception and response) processes and that diversity is thus structured by the species light-demand and affinity for the risk. Using a wide sample of 16 species, at the Paracou station, relevant functional traits - risk of not-self-supporting and gravitropic performance - are defined through adapted modellings which combine trunk shape, biomass distribution and wood properties. The traits values vary between species and also with ontogeny and saplings environment. These variations are due to elementary traits (shape, biomass, wood) with strong geometrical effects. The less self-supporting species (low mechanical security) have the highest gravitropic performances and are also the most light-demanders. A species, Tachigali melinonii, distinguishes itself by strong slendernesses and a frequent not-self-supporting habit letting suppose a strong adaptability to its mechanical environment. An experiment (growth response to staking), however, did not provide the expected results whereas the species with lower risks, Dicorynia guianensis, reacted more.
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Gaëlle Jaouen. Etude des stratégies biomécaniques de croissance des jeunes arbres en peuplement hétérogène tropical humide. Sylviculture, foresterie. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10118⟩. ⟨tel-01748253⟩



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