Effects of field-level strip and mixed cropping on aerial arthropod and arable flora communities

Loss of arthropod biodiversity can impair the provision of ecosystem services in agricultural landscapes. Crop diversification strategies offer the possibility to support arthropod communities without putting aside agricultural land as conservation areas. Within-field crop diversification measures, such as strip cropping and crop mixtures, may provide arthropods with continuity and diversity in food, shelter and habitat at fine spatial and temporal resolutions. However, it is unclear how strip cropping and plant species diversity within strips influences aerial arthropod and weed communities in commercially sized arable fields. In this 2-year study we tested the effects of crop heterogeneity on aerial arthropod and plant communities in organically managed strip fields. We tested effects of configurational crop heterogeneity by comparing sole cropping (MONO) with strip cropping (STRIP), and compositional crop heterogeneity by comparing STRIP with flower-legume-grain crop mixtures grown in strips (STRIPMIX). Aerial arthropod communities were assessed in 138 sweep net transects and plant communities in 124 vegetation plots in cabbage, wheat, sugar beet and barley. Higher configurational crop heterogeneity by strip cropping reduced herbivore abundances and increased natural enemy species richness in organic cabbage strips. Cabbage in MONO had a significantly higher herbivore abundance (+11%) and a lower natural enemy species richness (−57%) than cabbage in STRIP. Higher compositional crop heterogeneity by sowing additional plant species in strips (STRIPMIX) significantly increased plant abundance (+33%), plant species richness (+21%), total aerial arthropod abundance (+45%), and total aerial arthropod species richness (+21%) compared to STRIP. Our work shows that both configuration of crop areas (MONO vs. STRIP) and plant species diversity within strips (STRIP vs. STRIPMIX) can support arthropod biodiversity and natural pest suppression, but that arthropod responses differ between diversification strategies and crop combinations. Further optimization of design and management of within-field crop diversification strategies holds potential to attain biodiversity-based cropping systems which deliver multiple ecosystem services and have a reduced dependency on pesticides.