Improved field margins highly increase slug activity in Switzerland

Most field margins on arable land in Switzerland are narrow and intensively managed. As a consequence, field margins generally harbour few plant and animal species. To enhance biodiversity in arable landscapes, sown species-rich field margins, so-called improved field margins, were introduced in 2008 as a part of the Swiss agri-environment scheme. Here, we tested whether improved field margins increase slug activity density. Slug activity density in and next to improved field margins was compared to slug activity in and next to conventional field margins. Over a period of 3 years, slugs were sampled in three regions in northern Switzerland in late spring using bait stations. Our results show that improved field margins have higher slug activity density, of +191 %, than conventional field margins, independently of the region. The predominant slugs were Arion lusitanicus and Deroceras spp. While A. lusitanicus was generally more abundant in field margins than in fields, with intermediate numbers in the adjacent crop margins, Deroceras spp. showed a more even distribution.