Large scale application of diaspore transfer with plant material in restoration practice – Impact of seed and microsite limitation

Abstract

Seed and microsite limitation are seen as the main obstacles in the restoration of species-rich meadows. Past restoration projects of flood meadows along the northern Upper Rhine focusing solely on the re-creation of adequate site conditions were unsuccessful. In the present study, seed containing plant material was transferred on large scale of ca. 50 ha to former arable fields and some species-poor grassland to enhance species establishment. Additionally, we tested the effect of sward disturbance by rotovation in grassland and simultaneous sowing of grass at arable restoration sites. Four years after the application of plant material, 92 species were successfully re-established at the restoration sites, including 25 Red List species. Co-occurring vegetation had the highest impact on establishment success, with a negative effect of grasses. Establishment success at the arable fields was threefold higher than at grassland sites. In the latter, rotovation of the sward had only a small positive effect on establishment success. Simultaneously sown grass in former arable fields barely hampered establishment of plant material species. Although supply of phosphorus and potassium at the restoration sites was higher than at donor sites, we found no indication that this had negative effects on establishment success of plant material species. The transfer of plant material is a very effective measure to overcome dispersal limitation. A remaining obstacle for restoration are established swards with highly competitive species, whereas raised P and K levels seem to be tolerable in the case of limited N-supply at restoration sites.