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Influence du climat lors de l'investissement des ressources dans la reproduction chez les arbres forestiers : Une approche par modélisation mécaniste

Abstract : Long term climatic trends and extreme climatic events result in massive forest decline and can even lead to mortality. One of the major process of forest dynamics is sexual reproduction, which allows forest regeneration, determines the composition of forest community, and also the ability of tree populations to adapt locally to changing environmental conditions or to track their bioclimatic optimum through migration. However, there are still many uncertainties on the effect of climate change on trees reproduction, especially on when and how resources are allocated to pollen and seeds. The main objective of this PhD thesis is to develop an approach based on resource and phenology modelling, in order to understand and predict climate effects on forest trees reproduction. First, I used a statistical approach to investigate the drivers of temporal and spatial variation of fruit production in beech and oak stands. I found that the length of growing season is a limiting factor of fruit biomass production. In a second part, I quantified the allocation of resources between vegetative versus reproductive functions in the Atlantic cedar, using a hierarchical Bayesian model and observations of growth, male and female reproduction over several years. By explicitly accounting for inter-individual variation in the level of resources, this model allowed me to identify trade-offs between growth and reproduction during floral initiation, and between current and future reproduction. In the third part, I developed a process-based model of reproduction and included it in an existing biophysical and ecophysiological model of forest functioning (CASTANEA). The new reproduction model incorporates resource allocation and reproductive phenology from flower initiation to maturation, and simulates spatial and temporal patterns of seed production. The model was calibrated and validated on silver fir on Mont-Ventoux and used to investigate how climate change will impact fruit production. In the future, this model could be used at a larger scale to investigate the ecophysiological mechanisms involved in masting.
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Valentin Journé. Influence du climat lors de l'investissement des ressources dans la reproduction chez les arbres forestiers : Une approche par modélisation mécaniste. Biodiversité et Ecologie. Aix Marseille Université; ED 251, 2020. Français. ⟨tel-02537297⟩

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