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Studying phenology of tropical forest trees using a morphological and anatomical retrospective analysis: the case of Moronobea coccinea Aubl. (Clusiaceae)

Morel H., Mangenet T., Heuret P., Nicolini E.A.. 2016. In : Plinio Sist (ed.), Stéphanie Carrière (ed.), Pia Parolin (ed.), Pierre-Michel Forget (ed.). Tropical ecology and society reconciliating conservation and sustainable use of biodiversity. Program and abstracts. Storrs : ATBC, p. 117. Annual Meeting of the Association for Tropical Biology and Conservation (ATBC 2016), 2016-06-19/2016-06-23, Montpellier (France).

Most studies on tropical plant phenology have focused on patterns of flowering, fruiting and leaf-shedding. They are based on time consuming continuous surveys over seasons or years and the basic considered scale is the tree integrated within a population or a community. So, the functioning of the different axis categories inside the crown of one individual have been poorly considered and studied. Here, we want to demonstrate the efficacy of a retrospective analysis based on morpho-anatomical growth markers coupled with a field survey to study phenology and growth at different scales from within-individual to populations. In French Guiana, we collected dominant branches from 5 Moronobea coccinea adults, a hemi-tolerant tree of Neotropical rain forests. We identified growth markers delimiting longitudinal and radial increments. We coupled this retrospective analysis with a 30-month survey of (i) leaf-shedding and primary growth on twenty-two trees every month and (ii) for the repeated collecting of microcores from five trees every fifteen days to determine intra-annual cambial activity (i.e. formation of secondary xylem). Successive growth units and growth rings were identifiable based on morpho-anatomical markers. These structural regularities traduce the phenological cycle defined by leaves shedding, growth-unit elongation and growth-ring formation. The retrospective analysis was few time consuming and in comparison we reconstructed the tree growth history of individual trees in only two weeks. Our study shows that retrospective analysis and field survey are two complementary approaches to understand plant phenology and to interpret morpho-anatomical structure. Dating a branch by counting the number of growth units or growth rings is possible in many years with a reasonable error. Nevertheless, estimating their precise month of formation in order to study climatic influences remains difficult if a growth monitoring isn't coupled in the same time. The cycle of M. coccinea is essentially a biennial, with some slight variability: first year, the trees shed their leaf whereas the following years, trees flowers. At the population scale, trees were unsynchronized and the relationship between primary and secondary growth aren't clear. Surprisingly, we found an asynchronous phenological cycle between axes mainly due to flowering. (Texte intégral)

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