In recent decades, agricultural intensification has led to a strong decline in biodiversity. Agricultural field margins, defined as the uncultivated herbaceous vegetation located between the cultivated strip and an adjacent habitat, usually constitute an important refuge for biodiversity in highly disturbed landscapes, and are critical to the preservation of ecosystem services. However, field margins are also strongly impacted by agricultural practices in their immediate vicinity. Agricultural impacts are often studied at local to landscape scales, and rarely include national or larger spatial extents, where one of the challenges is the lack of availability of standardized monitoring efforts including both biodiversity and agricultural practices. Here, we take advantage of one such monitoring effort to assess the effects of agricultural practices on field margin flora at different extents and resolutions in continental France. We used spatial simultaneous autoregressive and generalized dissimilarity models to assess the response of species richness and community composition to climatic, soil, landscape, agricultural (fertilization, herbicides) and margin management factors. Analyses were repeated at the plot-level, as well as at 25, 40, 60 and 75 km resolutions, and at regional and national extents. We found that species richness is better explained by agricultural practices at the plot-level, and by climate and crop diversity at coarse resolutions, whereas composition responds more strongly to climate at the plot-level, and to fertilization and crop diversity at coarse resolutions. There was a strong variation in the explanatory percentage among regions, but climate effects tended to be weaker within biogeographic units compared to the national level. This allows a better understanding of landscape and management effects, and reveals interactions between local and regional effects. We suggest that providing an agricultural regulatory framework at the scale of biogeographic subdivisions could help provide pertinent measures to conserve biodiversity that are better adapted to the regional context.

Over the past decades, agricultural intensification and climate change have led to vegetation shifts in Europe. However, these impacts are often studied using meta-analyses at large scales, or using taxonomic diversity. Functional trade-offs linking traits responding to climate and farming practices are rarely analyzed, especially on large-scale empirical studies. Here we used a standardized yearly monitoring effort of agricultural field margin flora at the national scale to assess the spatio-temporal response of diversity and functional traits to climatic and agricultural variations. We examined temporal trends in climate, agricultural practices, plant species richness, and trait community-weighted means and variances across 555 sites in France between 2013 and 2021. We found that temperatures have increased while soil moisture has decreased, reflecting current climate change, whereas the intensity of agricultural practices did not show clear temporal trends over the past decade. Changes in plant communities were noticeable, especially as they relate to climate change, while the impact of agricultural practices was limited and mainly exerted through field margin management and to a lesser extent, fertilization. Mediterranean sites, vineyards and perennial species demonstrated reduced response to climatic variations. Our findings suggest that species adapted to climate change (including Mediterranean species) have increased in proportion and are spreading northward. Importantly, we identified functional trade-offs suggesting that these species are also the most vulnerable to intensive agricultural practices. We put these results into the conceptual framework of Grime’s CSR triangle and suggest that the convergence of climate change and the maintenance of a highly intensive agriculture could carry a risk of abrupt declines in floristic diversity of field margins, a concern that merits further attention.