Data from: Turnover and nestedness drive plant diversity benefits of organic farming from local to landscape scales

Biodiversity-benefits of organic farming have mostly been documented at
the field scale. However, these benefits from organic farming to species
diversity may not propagate to larger scales, because variation in the
management of different crop types and semi-natural habitats in
conventional farms might allow species to cope with intensive crop
management. We studied flowering plant communities using a spatially
replicated design in different habitats (cereal, ley and semi-natural
grasslands) in organic and conventional farms, distributed along a
gradient in proportion of semi-natural grasslands. We developed a novel
method to compare the rates of species turnover within and between
habitats, and between the total species pools in the two farming systems.
We found that the intra-habitat species turnover did not differ between
organic and conventional farms, but that organic farms had a significantly
higher inter-habitat turnover of flowering plant species compared to
conventional ones. This was mainly driven by herbicide-sensitive species
in cereal fields in organic farms, as these contained 2.5 times more
species exclusive to cereal fields compared to conventional farms. The
farm-scale species richness of flowering plants was higher in organic than
conventional farms, but only in simple landscapes. At the inter-farm
level, we found that 36% of species were shared between the two farming
systems, 37% were specific to organic farms while 27% were specific to
conventional ones. Thus, our results suggest that that both community
nestedness and species turnover drive changes in species composition
between the two farming systems. These large-scale shifts in species
composition were driven by both species-specific herbicide and nitrogen
sensitivity of plants. Our study demonstrates that organic farming should
foster a diversity of flowering plant species from local to landscape
scales, by promoting unique sets of arable-adapted species that are scarce
in conventional systems. In terms of biodiversity conservation, our
results call for promoting organic farming over large spatial extents,
especially in simple landscapes, where such transitions would benefit
plant diversity most.