Agricultural drivers of field margin plant communities are scale dependent

Abstract

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.