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Impact d'une mise en defens temporaire de prairies permanentes durant le pic de floraison : sélection alimentaire des brebis, diversité floristique et entomologique (Lepidoptera, Bombidae, Carabidae) des couverts

Abstract : Biodiversity loss in grasslands is a major concern across Europe. Sheep grazing is rarely considered the best method for delivering conservation objectives, as the result of their strong diet selection on forbs and legumes, which in turn negatively impacts nectar-dependent insect groups. Compared with cattle, sheep also produce a strong homogeneization effect and reduce habitat diversity. The objective of this thesis was to analyze the feasibility and environmental benefits of a rotational grazing management, in which sheep were temporarily excluded from a sub-plot at flowering peak. It was compared with continuous grazing in the same stocking rate. In addition, to measurements of animal performances and biodiversity indicators (plants, butterflies, bumblebees and ground beetles), we analyzed diet selection by ewes in the two grazing managements, and how sheep breed and soil fertility could modulate biodiversity outputs in the rotational management. Independently of sheep breed, the ewes increased their selection of forbs and legumes in rotationally-grazed plots. This rapidly decreased plant species richness in rotationally compared with continuously-grazed plots. However, an increase of flowering intensity in temporarily ungrazed sub-plots benefited bumblebee density and species richness, as predicted by the ‘trophic level’ hypothesis. Rotational grazing management did not increase butterfly and ground beetle densities, which stresses that its benefits would be lesser than in cattle-grazed systems. Defining the exclusion period based on the flowering of indicator plant species, modulating its duration based on spring grass growth, and keeping some sub-plots ungrazed until the end of the grazing season are options that still need to be tested in order to define the optimal conditions for such a rotational grazing management.
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https://tel.archives-ouvertes.fr/tel-00708561
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Submitted on : Friday, June 15, 2012 - 11:57:30 AM
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Alexandra Scohier. Impact d'une mise en defens temporaire de prairies permanentes durant le pic de floraison : sélection alimentaire des brebis, diversité floristique et entomologique (Lepidoptera, Bombidae, Carabidae) des couverts. Sciences agricoles. Université Blaise Pascal - Clermont-Ferrand II, 2011. Français. ⟨NNT : 2011CLF22210⟩. ⟨tel-00708561⟩

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