Effects of crop type and production method on arable biodiversity in boreal farmland

Crop choice affects biodiversity within fields due to crop-specific characteristics and management practices. However, there is a lack of studies systematically comparing the biodiversity value of different crops across multiple taxa. This study empirically compared the diversity of plants, pollinators, predatory arthropods, and multi-taxa diversity between seven crop types and long-term environmental fallows in boreal farmland. The effects of crop production method (organic vs. conventional) on biodiversity were also examined. Biodiversity data were collected in 78 fields in Southern Finland. The studied species groups differed in their preferences for crop types and fallows, but none of them was particularly associated to spring cereal (oat), the dominant arable crop in the boreal farmland. Environmental fallows had the highest plant species richness and butterfly abundance, whereas faba bean and oilseed crop fields attracted high numbers of bumblebees. Carabid beetles were most abundant in winter cereal (rye) fields, and spiders in perennial crop types. Multi-taxa diversity was highest in fallows and lowest in spring cereal (oat), ley and cabbage fields. Organic production increased plant species richness across crop types. Hoverflies responded to the interaction of production method and crop type, being most abundant in organically managed faba bean fields. The other species groups and multi-taxa diversity were not affected by the production method. High arable land cover in the surrounding landscape had negative effect on butterflies, solitary bees and carabid beetles within fields. Our results suggest that diversifying cropping systems to include more insect-pollinated crops, winter cereals and pastures, and increasing the area of environmental fallows while maintaining landscape heterogeneity would enhance resource provision for a variety of organism groups in boreal agricultural landscapes.