Impacts of agricultural intensification on arable plants in extensive mixed crop-livestock systems

•Land-use intensity affected rare segetal species.•Field edges hosted more segetal species than inner-field.•This difference significantly increased with land-use intensity.•Application of herbicides was the farming practice most detrimental to segetal species.•Species diversity was better explained by historic than current farming practices. Populations of segetal species are facing sharp declines in Europe due to agricultural intensification. To better conserve them, it is important to assess the effect of intensification in extensive mixed crop-livestock systems, which are considered hotspots for segetal species. The aim of this study was to evaluate how certain key farming practices and land-use intensity affect the composition, species richness and abundance of segetal species, taking into account spatial heterogeneity within the studied fields. To do this, we sampled 94 winter cereal fields - 41 farmed organically and 53 farmed conventionally - along a gradient of land-use intensity. At field scale, we found that both the species richness and the abundance of segetal taxa decreased with an increase in land-use intensity. The results also showed significant differences in segetal taxa composition, species richness and abundance between the edges and the inner-fields location and these differences significantly increased with land-use intensity. The species richness and abundance of both common and threatened segetal taxa were significantly higher at the edges of fields than within them. Herbicide treatments had a significant negative impact on segetal taxa species richness and abundance, while mechanical weeding had a positive impact on abundance. Nitrogen inputs had a significant detrimental effect only on the abundance of common segetal taxa. Crop seed origin and the ratio of cereal crops in the rotational cycle had no effect on segetal taxa species richness and abundance. Despite these impacts, we found that segetal species richness and abundance were better explained by farm identity (random factor) than by current management (fixed factors). Variation in segetal species richness and abundance between fields of the same farm and between farms reflect the long-term effects of farming practices and the history of seed transfer between farms more than by current management practices. In our study area, the production of cereals is destined for the consumption of the farm's sheep and the fact the cereals are not marketed makes it possible to tolerate