Temporal revegetation of a demolition site—a contribution to urban restoration?

In urban areas, open space including brownfields often became rare due to increasing urbanisation. Urban brownfields can be important for biodiversity, but especially brownfields in early successional stages seem to be refused by urban residents due to their sparse vegetation and less aesthetic appearance. The aim of this study was to revegetate a young demolition site in the city core of Osnabrück, Germany and thereby to support native plant diversity and aesthetic values. We developed two seed mixtures of native plant species and tested them in a large-scale field experiment over two growing seasons. Both seed mixtures developed towards structurally diverse and flower-rich vegetation. Establishment rates of sown species were consistently larger than 75%. Revegetation of the predominantly bare anthropogenically transformed soil by introduced species occurred fast. Vascular plant cover and vegetation height were higher on sown plots than in controls, but did not differ between the seed mixtures. Seeding did not increase plant species richness and did not reduce the establishment of a potentially invasive non-native plant species. The cover of Red-List species from the spontaneous vegetation was significantly higher in control plots. Our results indicate that not all aims can be reached on one restoration site. It has to be discussed if it is better to invest a restoration budget for measures aiming to increase acceptance of endangered pioneer plant species from the spontaneous vegetation or to introduce more attractive and more competitive species of later successional stages