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Theses

Impact du pâturage sur la structure de la végétation : Interactions biotiques, traits et conséquences fonctionnelles.

Abstract : Semi-natural grasslands constitute some multifunctional spaces which provide numerous benefits to society. Together with their obvious economic interest, semi-natural grasslands support a high plant and animal biodiversity. Grazing can constitute a sustainable management tool for these habitats, fitting well with conservation and restoration targets, and together able to satisfy agronomical issues. Within this global framework, this thesis intended to get a better understanding of plant communities response to grazing and of the resulting consequences on ecosystem functioning. Three plant communities encountered in a wet grasslands situated in the Marais Poitevin on the French Atlantic coast constituted the biological model. Studying the impact of grazing on plant communities and the resulting consequences on ecosystem functioning required to consider two important issues of community ecology : (i) community assembly rules, and (ii) the relationship between community structure and ecosystem functioning. Accordingly, a functional approach of plant community structure considering plant traits was used. Grazing increased plant diversity and richness in all three studied communities. Within each community, the spatially heterogeneous grazing pattern of herbivores (cattle and horses) led to a mosaic of vegetation patches differing in species composition and relative abundances. The positive impact of grazing on plant diversity and richness resulted from both (i) the floristic and species abundances contrasts between patches and (ii) the impact of grazers on plant diversity at the patch scale. Floristic contrasts observed among patch types resulted from the variation of the importance of the various environmental filters associated to grazing, in particular biomass loss rate and inter-specific competition. Grazing intensity enhancement led to the replacement of dominant species characterized by traits associated to slow growth, efficient conservation of internal resources and high ability to compete for light, by dominant species characterized by traits associated to fast growth, rapid resource acquisition and high root competition ability. Grazing effect on within-patch diversity could result from the reduction of competition for light, and from the fine-scale heterogeneity that grazers generate. The spatially heterogeneous grazing pattern led to a heterogeneity of ecosystem processes. The species structure of the vegetation patches could be linked to some parameters of the carbon and nitrogen cycles. In particular, the traits of the dominant species were found as an important determinant of the studied functional processes. Plant trait diversity appeared less determinant than traits of the dominant species for such processes. This work constitute a step toward a predictive approach of grazing impact on plant community structure and ecosystem functioning which can contribute to conciliate ecological, environmental and agronomic issues.
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Submitted on : Wednesday, February 16, 2011 - 5:14:57 PM
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  • HAL Id : tel-00566651, version 1

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Benoit Marion. Impact du pâturage sur la structure de la végétation : Interactions biotiques, traits et conséquences fonctionnelles.. domain_other. Université Rennes 1, 2010. Français. ⟨tel-00566651⟩

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