DYNAMIQUES TEMPORELLES DES COMMUNAUTÉS VÉGÉTALES FORESTIÈRES EN RÉPONSE AUX CHANGEMENTS GLOBAUX. APPROCHE COMPARATIVE ENTRE BRYOPHYTES ET TRACHÉOPHYTES VIA L'ÉCOLOGIE HISTORIQUE

Abstract : For at least the past two centuries, human activities have caused strong environmental changes in the biosphere. Many studies have shown responses of vegetation to global changes. However, many unknowns remain. First, most explicitly temporal studies have been conducted at a single site with a common intensity of environmental changes and historical land-use legacies. Results are highly variable among studies, and we have a very limited understanding of mechanisms underlying this variation. Second, despite the major contribution of bryophytes to ecosystem functioning, very few temporal studies have focused on bryophytes. This Ph.D. contributes to filling these two knowledge gaps. The overarching question for the three research projects presented here is: what is the impact of environmental change on biodiversity? We built a set of hypotheses around two main questions: (i) What is the effect of environmental changes on forest vegetation? (ii) Which taxon, bryophytes or vascular plants, is most sensitive to global changes? Chapter 2 tests the hypothesis that bryophytes are more sensitive than vascular plants to the combination of atmospheric deposition and warming in an industrial region in north-eastern France. Chapter 3 tests the hypothesis that forest vegetation changes have been greatest in regions with the strongest warming trends along a continental gradient in eastern Canada. The last chapter combines the two first approaches, quantifying temporal changes in bryophyte and vascular plant communities in sites with different warming intensities along elevational gradients in eastern Canada. To answer to these questions, I used an historical ecological approach by resurveying botanical plots initially surveyed in the 1970s. Plot selection followed a reproducible and detailed procedure to minimize confounding factors. Our results show a direct effect of global changes on forest vegetation. First, bryophytes appear more sensitive to atmospheric deposition than vascular plants (Chapter 2). Second, temporal changes in vascular plant communities were stronger in areas where warming has been greatest (Chapter 3). Third, in response to warming, changes in bryophyte and vascular plant communities show idiosyncratic differences, depending on the community property under study (Chapter 4). Results of the three chapters clearly show systematic changes in community composition, that are not necessarily accompanied by changes in local diversity. In sum, we provide empirical evidence that historical ecology is a powerful method to disentangling mechanisms of vegetation response to global changes. Only a holistic approach based on different biodiversity components, different spatial scales and wide variety of community properties permit an understanding of the complexity of temporal dynamics of vegetation.
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Antoine Becker-Scarpitta. DYNAMIQUES TEMPORELLES DES COMMUNAUTÉS VÉGÉTALES FORESTIÈRES EN RÉPONSE AUX CHANGEMENTS GLOBAUX. APPROCHE COMPARATIVE ENTRE BRYOPHYTES ET TRACHÉOPHYTES VIA L'ÉCOLOGIE HISTORIQUE. Biodiversité et Ecologie. Université de Sherbrooke, 2018. Français. ⟨tel-02143219⟩

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