Changements globaux et dynamiques forestières des pessières du Québec au cours des 8000 dernières années à partir d'approches paléoécologiques et biogéochimiques

Abstract : In order to better figure out the ongoing transition of the boreal forest in northern Quebec and to identify the responsible factors, this thesis studied the dynamics, stability and resilience of the two forest ecosystems at stake, over time. These ecosystems, the closed-canopy dense moss forest and the open lichen woodland, share the same dominant tree species (black spruce, Picea mariana). The thesis focused on the development of innovative geochemical tools in palaeoecological studies that could track present and past terrestrial ecosystem structure and composition, and then focused on the reconstruction of past fire regimes through lacustrine charcoal analyses. A first step demonstrated that the soils of both ecosystems displayed distinct physical and chemical properties and are maintained by the feedback interactions in the soil-vegetation-climate system. The second step showed that modern sediments of study lakes recorded variations in their chemical composition depending on whether they were surrounded by moss forest or lichen woodland. Using the so calibrated geochemical proxies, the third chapter reconstructed the vegetation and fire histories during the Holocene. A major disruption in ecosystem structure was evidenced 4500-4000 years calibrated before present and led to the conclusion of a boreal forest opening at that time due to an increase in fire frequency. The precariousness of the present states stability is discussed in light with the current context of fire increase in the study region and suggests that forest management should be adapted consequently.
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Carole Bastianelli. Changements globaux et dynamiques forestières des pessières du Québec au cours des 8000 dernières années à partir d'approches paléoécologiques et biogéochimiques. Ecosystèmes. PSL Research University; Université du Québec à Abitibi-Témiscamingue, 2018. Français. ⟨NNT : 2018PSLEP044⟩. ⟨tel-02165034⟩

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