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.

Data about flowering plant communities collected in cereal fields, leys and semi-natural grasslands and used for the analyses.

Authors:

Name: Romain Carrié
Insititution: Centre for Environmental and Climate Research, Lund University
Email: romain.carrie@cec.lu.se (corresponding author)

Name: Johan Ekroos
Insititution: Department of Agricultural Sciences, Plant Production Sciences, University of Helsinki

Name: Henrik Smith
Insititution: Department of Biology, Lund University

Two files:

• data_Carrie_et_all_Ecol_Appl_dryad: contains the data for the analysis on flowering plant species richness (habitat and farm scales) and the proportion of exclusive species at the plot, habitat and regional scales.
• data_traits_Carrie_et_all_Ecol_Appl_dryad: contains the same data but for each trait (herbicide and nitrogen sensitivity), at the habitat and regional scales.

Tabs for the file data_Carrie_et_all_Ecol_Appl_dryad:

• species richness habitat: Flowering plant species richness at the habitat scale
• species richness farm: Flowering plant species richness at the farm scale
• exclusive plot: proportion of plot-exclusive plant species per habitat type and farming system (intra-habitat turnover)
• exclusive habitat: proportion of habitat-exclusive plant species per habitat type and farming system (inter-habitat turnover)
• exclusive farming syst: proportion of farming system-exclusive plant species for each possible organic-conventional farm pair (regional turnover)

Tabs for the file data_traits_Carrie_et_all_Ecol_Appl_dryad:

• herbicide excl habitat: proportion of herbicide sensitive/tolerant habitat-exclusive plant species per habitat type and farming system (inter-habitat turnover)
• nitrogen excl habitat: proportion of nitrogen sensitive/tolerant habitat-exclusive plant species per habitat type and farming system (inter-habitat turnover)
• herbicide excl farming system: proportion of herbicide sensitive/tolerant farming system-exclusive plant species for each possible organic-conventional farm pair (regional turnover)
• nitrogen excl farming system: proportion of nitrogen sensitive/tolerant farming system-exclusive plant species for each possible organic-conventional farm pair (regional turnover)

Variables

• farm.ID: farm ID
• Habitat.type: Habitat type sampled (cereal, ley and sng = semi-natural grassland)
• Farm.syst: farming system of the corresponding farm (org = organic, conv = conventional)
• p.SNG: average proportion of semi-natural grasslands around the sampling plots
• flower.SR: Flowering plant species richness (response variable)
• p.excl: proportion of exclusive flowering plant species (plot, habitat and regional scales) (response variable)
• Sensitivity.MCPA: sensitivity to the MCPA herbicide (MCPA is one of the most used herbicide in Sweden), measuring herbicide sensitivity in the analysis (Y = sensitive, N = non-sensitive).
• Family: plant species family (Legume, Non-legume) measuring nitrogen input sensitivity in the analysis (Legume = nitrogen sensitive, Non-legume = nitrogen tolerant).

Variables specific to tab 'exclusive farming syst' in file 'data_Carrie_et_all_Ecol_Appl_dryad'

These variables are calculated at the scale of a farm pair (conventional-organic pair)

• Id.pair : ID of the conventional-organic farm pair
• Farm.ID.conv: ID of the conventional farm
• Farm.ID.org: ID of the organic farm
• sr.conv: Flowering plant species richness of the conventional farm
• sr.org: Flowering plant species richness of the organic farm
• nb.shared: Number of shared species between the two farms of the pair
• p.shared: Proportion of shared species between the two farms of the pair  (response variable, Fig. 6b)
• sr.change: Change in species richness when shifting from conventional to organic (response variable, Fig. 6a)
• p.excl.org: proportion of exclusive flowering plant species to the organic farm in the pair (response variable, Fig. 6b)
• p.excl.conv: proportion of exclusive flowering plant species to the conventional farm in the pair (response variable, Fig. 6b)