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Microanalyse à haute résolution du bois et dendrochronologie des arbres tropicaux

Abstract : Because of their dominant role in the global carbon cycle, changes in tropical forest dynamics can affect the pace of the climate changes.Today, the only estimation of tropical tree growth comes from permanent plot networks. However, their installation is still much too recent (i.e. beginning of the 80’s for the oldest stations) to provide long enough temporal series to answer primordial, yet unsolved questions. Is tropical tree growth controlled by climate variations? Are tropical forests showing long-term changes of their productivity as temperate forests do? What are the impacts of the global changes on tropical forest functioning? An even more basic question is still fully unsolved: how old are tropical trees? Nevertheless, not any sustainable exploitation and management of the tropical forest resources is conceivable without knowing the age of the harvested trees. The dendrochronology approach (i.e. the study of annual rings in trees) was remarkably successful in solving these questions for temperate climate trees. The retrospective analysis of tree growth patterns not only gives direct access to the age of the trees, but allows reconstructing the past effects of the environment on tree physiology over decades or even centuries. However, insurmountable difficulties to identify annual growth rings in most tropical trees (due to nearly constant growth rates over the year) prevented dendrochronologists from using the classical method of ring width measurements. As we urgently need to understand the effects of the ongoing changes in climate and atmosphere on tropical forest, it appears especially important to develop new techniques for tropical dendrochronology. The objective of the project was to evidence the existence of cyclic chemical signals in tropical wood that could compensate for the lack of visible growth rings. The potential of dendrochemical analysis for emphasizing reliable markers of seasonal cycles was tested on trees of known age from three different species: two major long-lived species of the Guianan-Amazon tropical wet forest (Dicorynia guianensis, Sextonia rubra) and one from the equatorial African forest (Pericopsis elata). The analyses were performed at the DiffAbs beamline using synchrotron monochromatic X-ray beam of energy 18.1 keV. For each wood sample, the radial distribution of 17 elements was analyzed from the bark to the pith with a 300 μm spatial resolution using a Silicon Drift Detector. The results showed that these ringless tropical trees, by displaying seasonal variations in wood element composition, can yet keep an archive of their past growth. Compared to the only previous report established on one single tree, the current study, based on 13 trees, constitutes a much more robust assessment.
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https://hal.inrae.fr/hal-02739769
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  • HAL Id : hal-02739769, version 1
  • PRODINRA : 320433

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Stéphane Ponton, Christophe Rose, Jean-Luc Dupouey, Alexandre Giuliani, Dominique Thiaudière, et al.. Microanalyse à haute résolution du bois et dendrochronologie des arbres tropicaux. INRA-SOLEIL: the synchrotron approach in agriculture, food and environment sciences. INRA-SOLEIL2015, Jan 2015, Saint-Aubin, France. 23 p. ⟨hal-02739769⟩

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