The soil seed bank and its relationship to the established vegetation in urban wastelands

Industrial and traffic areas are particularly characteristic of the urban environment. Due to frequent soil transport and vegetation disturbance, soil seed banks and seed production play an essential role for vegetation establishment in these sites. Since researchers have scarcely focussed on these traits, it was analysed in three railway and loading areas in Munich. Seed numbers in soil ranged from 1300 m−2 on ruderalized calcareous grassland at Virginia Depot to 2800 m−2 on the rail track beds in Steinhausen and 7600 m−2 on ballast and calcareous gravel at Gleislager Neuaubing. The corresponding annual seed production was 17 000, 50 600 and 49 400 seeds m−2, respectively. The seed bank of all three sites was dominated by biennial and perennial ruderals, and species naturally growing on rocky or sandy habitats. Grassland species and woody plants frequently grew in the established vegetation but scarcely occurred in the soil samples. The abundance of invasive alien species in the seed bank significantly exceeded their share in the vegetation. The seed banks also harboured endangered plants. Differences between the seed bank and the established vegetation reflect ongoing succession. While the seed bank was mainly composed of persistent seeds of early-successional plants, the established vegetation was dominated by long-lived species with transient seeds that increasingly suppress regeneration of the short-lived species. These results imply that recurring soil disturbance could re-activate the seed bank of both alien and endangered plants. Consequences for vegetation management and nature conservation are discussed.

Research highlights▶ High seed production vs. low seed bank values indicate severe seed losses. ▶ Succession selects for a high seed longevity in soil and a low one in the vegetation. ▶ The soil seed bank harboured high percentages of alien and endangered species. ▶ Alien and rare species declined during succession can be re-established by soil disturbance.