Restoration of wet grasslands - Effects of seed dispersal, persistence and abundance on plant species recruitment

Restoration projects in previously intensively used wet grassland areas in Europe showed that the re-establishment of target plant species can be strongly limited by propagule dispersal. In a large wet grassland area in Northwest Germany (Borgfelder Wummewiesen, 677ha) with relatively intact habitat conditions and extensive inundations it was tested whether the re-establishment of grassland species during restoration succession depends on population density in the established vegetation, the ability to survive in the soil seed bank, or on long-distance dispersal through inundations. For this purpose species recruitment was recorded in 58 permanent plots over a period of 6 years. In a multiple regression, species frequencies in the established vegetation (a measure for population density), frequencies in the drift line (dispersal capacity by winter inundation) and seed persistence in the soil were used as predictors for recruitment rates. Recruitment was mainly controlled by poputation density in the established vegetation. Long distance dispersal by means of winter floods and a tong seed bank persistence contributed Less (but still significantly) to the recruitment rates. Propagation by means of stolons and adaptations to hydrochory had a positive effect on recruitment rates and frequencies in the drift Line. High recruitment rates of target species in the test area, compared with other grassland areas of a more intensive land use history, emphasize the importance of a big species pool and the spatial interconnection of species-rich (source-) and species-deficient (sink-) habitats. Many target species, however, exhibited low recruitment rates because their ability to disperse in time and space is low. Restoration management for wet grasslands should, therefore, focus on large areas with a short intensification history and remnants of target species populations, which are connected with sink habitats by inundations. (c) 2006 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved.