Infodoc : Sciences, Techniques et Culture

Biodiversity is decreasing dramatically worldwide with land use change and habitat degradation being among its major causes. In Europe, this biodiversity loss is strongly related to the intensification of agriculture which has led to the simplification of landscapes. This resulted in the homogenization of landscapes where only a few crops dominate, accompanied with an increase of field size. Natural and semi-natural landscape elements, such as hedgerows, vegetation strips and groves were withdrawn, while more and more grasslands were being cropped or abandoned. Yet, grasslands are important functional biodiversity providers for crops in agricultural landscapes, including species that can provide ecosystem services such as pest control or pollination to farming activities. This PhD the[...]

Biodiversity is decreasing dramatically worldwide with land use change and habitat degradation being among its major causes. In Europe, this biodiversity loss is strongly related to the intensification of agriculture which has led to the simplification of landscapes. This resulted in the homogenization of landscapes where only a few crops dominate, accompanied with an increase of field size. Natural and semi-natural landscape elements, such as hedgerows, vegetation strips and groves were withdrawn, while more and more grasslands were being cropped or abandoned. Yet, grasslands are important functional biodiversity providers for crops in agricultural landscapes, including species that can provide ecosystem services such as pest control or pollination to farming activities. This PhD thesis therefore aimed at disentangling the influence of field and landscape parameters on the arthropod communities of adjacent grasslands and croplands of agricultural landscapes.We sampled arthropods from pairs of neighboring cereal fields and grasslands in order to compare the field and landscape influences on the biodiversity of these two agricultural land cover types. Our research took place in three study regions of southeastern France, each of them representing a different gradient between annual winter cereal crops and permanent grasslands. We mainly focused on carabids, though we also studied to some extent ground-dwelling spiders as well as pollinators such as hoverflies and lacewings. The landscape parameters were based on a land cover recording of cropped, grasslands and (semi-)natural areas and linear elements 500 m around every sampled location.Concerning carabids, cropland and grassland assemblages remained mainly distinct, but they showed higher similarity when located closer, up to 4 km from each other. Carabid activity-density was higher in the study regions with higher grassland coverage. In grasslands, we found a higher species richness when the landscape diversity around was increased, except for the study region which was strongly dominated by grassland. In winter cereal crops, the landscape parameters showed no significant effect on carabid species richness. Moreover, the common species richness in neighboring cereal fields and grasslands was enhanced by higher density of field borders between these two land cover types in the studied landscapes. Though the land cover type was by far the major determinant of carabid traits, landscape parameters also had a significant influence. Polyphagous species tended more to be commonly appearing in neighboring grassland and cereal crop. Phytophagous species were highly exclusive to grasslands, while predatory were it in cereal crops.Regarding other arthropod groups, we observed that the spider family richness was higher in permanent grasslands, though there were more individuals caught in cereal fields. Both hover flies and lacewings sampled density were higher in cereal fields and lower in the neighboring of higher grassland coverage.This thesis indicates that the preservation and restoration of a mosaic of permanent grasslands within diversely cropped landscapes is important for functional biodiversity. The inclusion of grasslands can enhance the diversity of beneficial arthropods and provide complementary resource and habitats to communities for pest control in crops.