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Résumé :
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Extensive grazing by domestic herbivores is a widespread management practice used since the 80s in many European agro-ecosystems such as semi-natural grasslands to maintain open habitats and to enhance biodiversity. Such grazing systems have principally been tested in cultural ecosystems of high nature value threatened by grazing abandonment. However, there have been few case studies of grazing management in very anthropized ecosystems, such as the new ecosystems created by urban or industrial conversions. In Southern France, by the lower part of the Rhône river, since 1999, different low-intensity grazing management systems using rustic breeds of cattle, horses and goats have been tested on a protected reserve of 1454 ha located in the lower part of the Rhône river. Extensive grazing, more than cutting or no management, positively modified vegetation heterogeneity (beta-diversity), the target open grassland species, but not plant species richness (alpha-diversity). However, the current monitoring shows that these benefits of grazing will be confirmed only if low-intensity grazing systems are sustained and if new adaptations can be also made, such as the use of mixed stocking and the establishment of multiyear contracts with breeders./La mise en place d'une gestion par le pâturage de la végétation de la réserve de Donzère Mondragon et la comparaison avec la coupe. Le pâturage se révèle meilleur que la coupe pour augmenter l'hétérogénéité (diversité Beta ) mais, pour l'instant, ne modifie pas significativement la richesse spécifique (diversité alpha). La mise en place d'un pâturage pluri-espèces est suggéré afin d'augmenter l'efficacité du pâturage domestique.
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