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Theses

Les communautés végétales des interfaces forêt-prairie et leur environnement face aux cas d'afforestation et de déforestation

Abstract : In temperate Europe, landscapes are dominated by a mosaic of forests, grasslands and crops since several centuries. This long period of time allowed the specialization of species within the habitats and their interfaces thanks to strong environmental contrasts. However, there have been frequent land-use changes in the past, which have accelerated in recent decades, challenging the stability of plant communities and their environment. The afforestation of former grasslands and the extension of grasslands by deforestation, mostly resulting from the progression and regression of the edges, have been poorly studied. In the forest-grassland interfaces, in addition to an edge effect induced in each habitat by the proximity to the adjacent habitat, a history effect can be added in recent habitats, i.e. an environmental and/or floristic legacy (extinction debt, colonization credit). In the recent habitat edges, an interaction between edge effect and history effect can also be encountered. In this thesis, the objectives were to evaluate the relative abundance of the edge effect and the history effect along forest-grassland interfaces stable, from afforestation process and from deforestation process, by studying (i) environmental conditions, (ii) the richness and floristic composition of plant communities, and (iii) trait values within communities. Our results showed increasing gradients of light intensity and soil nutrients ranging from grassland edges to grassland cores. In response to these gradients, a strong edge effect on the composition of plant communities was found in grasslands. These floristic differences between grassland edges and grassland cores are explained by the presence of a large number of transgressive species among the forest specialist species, which have trait values favoring their transgression in grasslands. Besides this, an extinction debt of grassland specialist species has been found in recent forests, which is responsible for a higher vegetative height compared to ancient forests. These results can be explained by the fact that light intensity remained higher in recent forests, even after several decades. An extinction debt of forest specialist species has also been demonstrated in the recent grassland edges, which is the result of an interaction between edge effect and history effect. In recent grasslands, the edge effect favors the maintenance of forest species. According to our findings, forest and grassland edges, most of which have been displaced over the past two centuries, are home to many plant species that are habitat specialists, sometimes in extinction debt. A re-evaluation of the distribution of species within forest and grassland plant communities then seems necessary, taking into account the history of habitats. In a context of increasing forests and grasslands instability, the identification of species in extinction debt represents an opportunity for the conservation and restoration of plant biodiversity
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Submitted on : Monday, September 11, 2017 - 4:33:06 PM
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Maxime Burst. Les communautés végétales des interfaces forêt-prairie et leur environnement face aux cas d'afforestation et de déforestation. Ecosystèmes. Université de Lorraine, 2017. Français. ⟨NNT : 2017LORR0078⟩. ⟨tel-01585592⟩

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