Factors influencing the plant and invertebrate diversity of arable field margins

Field margin plots, sown with either a simple grass mix, a complex grass mix with or without forbs or allowed to regenerate naturally were established around four fields on the Royal Agricultural College’s Harnhill farm in the west of England. Two of the fields were managed conventionally and two were managed organically. Plants and invertebrates were recorded on the margin plots over a 2 year period to test the influence of the different mixtures on the community assemblages. There was no difference in the seed bank of the different plot types, however the organically managed margins contained more unsown species than the conventionally managed margins. The simple mix plots had significantly fewer plant species than the other plots. The naturally regenerating plots had significantly lower grass cover and grass species diversity than the other plots. In the second year perennial grass and perennial forb cover increased in all mixtures. Both the cover and numbers of unsown species were reduced in the sown plots in the second year. Percentage cover and species richness of forbs were significantly higher in the complex grass with forbs and naturally regenerating plots. Auchenorrhyncha, Heteroptera and Araneae abundance were significantly correlated with plant species richness. Also, both plant species richness and total plant cover significantly influenced the Auchenorrhyncha community. Invertebrate abundance was greater in the organically managed plots than in the conventional ones, except larval Coleoptera. In the second year significantly more predatory Coleoptera species were trapped in the natural regeneration plots. Farming system and field crop type influenced the Coleoptera communities, phytophagous Coleopteran diversity being significantly correlated with plant diversity. Sowing field margins with a complex seed mixture with some forb species and managing the field with reduced inputs suppressed undesirable plant species and increased invertebrate abundance and diversity. A mixture containing forbs increased plant species richness and maximised heterogeneity of the margin, providing a more diverse habitat for invertebrates.