Decreasing diversity in the soil seed bank after 50 years in Danish arable fields

Side-effects of intensification have raised public concerns. Declining diversity and abundance of wild species and pollution have been reported worldwide. National surveys are necessary to assess the overall effect on the wild flora of the changing management of arable land. We studied how the plant diversity in 40 fields in Denmark has changed over a period of 50 years. Three surveys of the vegetation and the viable soil seed banks were conducted at the same locations in Danish fields in 1964, 1989, and 2014. The same methods were used to estimate the soil seed bank in the ploug layer and to describe the corresponding vegetation in the three surveys. Soil samples were placed in trays in a greenhouse for nine months, and the plants from germinating seeds were identified. Significant changes were found in the viable soil seed bank and the vegetation. A drastic decline of plant species and seeds was observed after the first 25 years. The frequency of species and the number of seeds were reduced considerably from 1964 to 1989. In 2014, the number of seeds in the soil seed bank had increased to the same level as in 1964, whereas the frequency of the species in the vegetation was at about the same level as in 1989. The species in the vegetation deviated partly from those found in the viable soil seed bank as the number of species recorded in both assessments made up only about 50% in all surveys. Relatively few species dominated and have been able to adapt to modern cultivation practice.