Biodiversity and agro-ecology in field margins.

During the last decades, structural, floristic and faunistic diversity of the agricultural landscapes in Northern and Western Europe has declined considerably owing to the intensification of agriculture from the 1950’s on. In reaction to biodiversity loss, EU policy pursuited the ecologisation and multifunctionality of agriculture. Field margins do pioneering work in the ecologisation of agriculture since they are the interface between intensive farming practices and the wider environment. The presented multidisciplinary study investigates agro-ecological functions (nature conservation, agriculture, environment) and implications of newly created, unfertilised, sown and unsown field margin strips installed on ex-arable land to increase biodiversity. Margin strips were mown twice a year with a late first cut on 15 June and a regrowth cut on 15 September to meet nature conservation purposes. From conservational concern, species diversity on the long term seemed unaffected by the type of plant community that was installed. The decrease in species diversity was more pronounced under a mowing regime without removal of cuttings. The annual addition of mown roadside herbage significantly enhanced species richness. Convergence in vegetation composition between sown and unsown plots occurred in terms of species importance. From agricultural concern, the importance of economically important weeds Elymus repens Gould, Cirsium arvense L. and Urtica dioica Scop. was significantly higher when cuttings were not removed and in the unsown community. Seed dispersal into the adjacent crop was only of importance one year after installation of the margin strips; seedrain was significantly 8 times higher nearby the unsown community than nearby sown communities. The feeding value of herbage from field margin strips was low compared to the feeding value of herbage harvested in agricultural managed fertilized grassland, limiting its use in rations for highly productive livestock. From environmental concern, the reduction of soil mineral N nearby the boundary by the presence of a margin strip was responsable for the increase in abundance of less competitive species and enrichment of species diversity within the semi-natural boundary.