Smart management is key for successful diversification of field margins in highly productive farmland

Abstract In highly productive farmlands, field margins could offer habitats and refuges for many plant and animal species. But species-rich field margins are rapidly declining due to field enlargements and unfavourable management practices. In European farmland, management is usually restricted to repeated mulching during the growing season or mulching once a year between September and February. Under nutrient-rich conditions, both methods benefit competitive perennial grasses at the expense of species richness. Diversification of species-poor grass margins on nutrient-rich sites is difficult to achieve and we lack evidence which method works best. Starting in late summer 2010, we implemented a large-scale field experiment on nutrient-rich Chernozem soil, where we examined the effect of sward disturbance intensity, sowing of target species, and mowing time on the development of field margin vegetation over seven years. After disturbance of the existing species-poor grass sward with two intensities (tilling once or three times), a seed mixture of 49 wild plants from a regional seed propagation was sown in early October 2010. After an establishment phase in 2011, the sites were mown once a year, in either June or September, with removal of biomass. In addition, both cutting times were applied to species-poor grass margins without disturbance and sowing treatments. We recorded the plant species composition yearly from 2010 until 2016. Although the early establishment rate of the sown species was higher on sites disturbed three times, the number of successfully established target species on sites with different sward disturbance intensities converged during the observation period. Mowing in September resulted in higher grass cover and considerably decreased the cover of the sown target species. On the other hand, mowing in June resulted in significantly higher plot occupancy and cover of the sown target species. In general, the immigration success of target forbs into adjacent undisturbed and unsown grass margins was very low even after seven years, although mowing once a year with biomass removal increased the number of mostly ruderal species. Diversification of grass margins was very successful with active species introduction in combination with initial sward disturbance and management adapted to nutrient-rich site conditions. Therefore, restored field margins in highly productive farmlands should be mown in early summer to sustain long-term biodiversity.