Early vegetation growth in an experimental restoration site in the Watarase wetland

Abstract

The Watarase wetland is a floodplain wetland in central Japan, mainly composed of moist tall grassland dominated by Phragmites australis and Miscanthus sacchariflorus. The restoration experiment was conducted to determine whether removal of topsoil, including the rhizomes and seed bank of the invasive species Solidago altissima, would lead to an increase in re-colonization of aquatic and short-lived wetland plants from the soil seed bank. We investigated species composition and vegetation development at the experimental site during 2 years after topsoil removal at five soil depths. At the experimental site, six aquatic and 31 short-lived wetland species, including 14 Red List species, were recorded. This suggests the effectiveness of topsoil removal for restoration of aquatic and short-lived wetland plants. During the study period, nine exotic species, including S. altissima, were recorded, but their species number and abundance decreased remarkably in the second year. Although species number and abundance mostly decreased significantly with removal depth, some species occurred only in deeper layers, suggesting the need to explore the topsoil removal depth required to increase wetland plant diversity for successful restoration.