COS 24-3 - Effects of agricultural practices on field margin biodiversity: synthesis from a long-term, large scale monitoring effort in France

Abstract: Agriculture has been one of the major drivers of land use changes associated with biodiversity loss, as well as one of the main contributors to nitrification and other main global changes. Keeping food production for a growing human population while minimizing agricultural impacts on the environment has therefore become a major challenge that needs empirical ecological solutions at multiple scales. Facing this challenge will require integrating large-scale monitoring studies to appropriately guide regulatory measures. Here we synthesize results from a national yearly monitoring effort that has gathered data on plant and coleopteran communities as well as agricultural practices in 500+ agricultural field margins across continental France between 2012 and 2022. Field margin communities are suitable to assess the effects of agricultural practices on biodiversity because they are in near proximity to managed fields, yet they can also provide refuge and stepping stone habitat for the most vulnerable species. Our results show higher diversity in field margins that are adjacent to organic farming; however, there is also great variability in terms of agricultural practices between and within conventional and organic farming, leading to much variability in the communities followed. We found that biogeographic region has a large influence on the final effects of agricultural practices on biodiversity. This reflects, for example, on the Mediterranean region being more vulnerable to nitrogen addition in agricultural fields, and less vulnerable to climate change over time, as compared to the rest of France. Efforts to regulate specific agricultural practices would therefore benefit from taking into account these regional differences. We have also found important indirect effects on coleopteran biodiversity, mostly mediated through plant diversity. Finally, our results also highlight a negative impact of pesticide and fertilizer drift on diversity and composition of plant communities. The effect of herbicide type depends essentially on the cropping system and their dominant type of herbicide, and some results suggest that alternating active ingredients of herbicides may help reduce their overall impact on plant diversity. In conclusion, this study suggests multiple ways in which agricultural practices could reduce their impact on surrounding biodiversity, and highlights the importance of taking into account regional species pools. We end by presenting our perspectives on how molecular identification methods can help us make our large-scale monitoring efforts more efficient in the long term, which is fundamental to help us maximize biodiversity around productive systems.