Effects of management on seed predation in wildflower strips in northern Switzerland

Abstract

Wildflower strips have been introduced to increase biodiversity in intensively used arable land in central Europe. Some wildflower strips are mown or harrowed to maintain species diversity. Management and associated changes in vegetation structure may affect seed predation which is a key factor in plant population dynamics. The aims of the present work were to (1) assess the magnitude and spatial variation of seed predation in managed wildflower strips, (2) identify the responsible seed predators, and (3) investigate differences between seed species. The study was conducted in five wildflower strips in northern Switzerland; the treatments were fallow, mowing and harrowing in winter. Permanent plots were established to investigate the vegetation structure, seed removal from selectively accessible dishes, and rodent abundance in life traps. Seeds of three arable weeds were offered which are used in wildflower seed mixtures ( Agrostemma githago, Camelina sativa, Centaurea cyanus). Seeds of Prunus avium were chosen to investigate exclusively predation by rodents. Losses of seed were recorded for one week in four experiments from June to August. Management had only a moderate effect on the structure of the vegetation in summer. Fallow and mown plots were similar and had a tall and dense canopy, whereas plant cover was sparse in the harrowed plots. A total of 101 plant species occurred, although most plots were dominated by Tanacetum vulgare and Elymus repens. In the harrowed plots annual species were more abundant (e.g., C. cyanus, Chamomilla recutita, Papaver rhoeas). The selectively accessible dishes revealed that rodents and slugs were the main seed predators. Predation by insects and passerine birds was negligible. Rodents strongly preferred C. cyanus, whereas slugs destroyed most seed of C. sativa. After one week seed losses amounted to 43–51% in C. sativa, 23–25% C. cyanus and 10–12% A. githago. The rank order of the species was similar for the three management treatments and both study periods. Predation of C. sativa was significantly reduced in the harrowed plots, whereas the losses of C. cyanus were independent of management. Live-trapping suggested that Apodemus flavicollis and A. sylvaticus were mainly responsible for seed predation of C. cyanus; Microtus arvalis avoided harrowed plots. It is concluded that only harrowing significantly affects the vegetation structure of wildflower strips and reduces seed losses, that seed predation by rodents and slugs is high, and that arable weeds are affected to a different extent.