Responses in plant and carabid communities to farming practises in boreal landscapes

The effect of organic farming compared to conventional mixed and cereal farming on arable weeds and carabid beetles in boreal landscapes was studied by comparing the distribution of ecological traits, diversity partitions, species richness and abundance. Organic farming increased both insect-pollinated as well as overall weed species richness, whereas the proportion of insect-pollinated weed species of the total species richness was unaffected by farming practises. Carabid species richness was mainly unaffected by farming practises although a higher alpha diversity of large and intermediate carabid species in organic and conventional mixed farms was marginally significant. Activity-densities of carabids were highest on conventional mixed farms. Landscape variables did not affect weed diversity but carabid beta diversity increased with increasing landscape heterogeneity. Local richness of large and intermediate carabid species showed a marginally significant decrease with increasing field cover. It is concluded that arable weed diversity is affected by organic farming to a higher extent than carabids.