Plant species richness in intensively managed temperate wet grasslands: current state and the importance of edge habitats

This study investigates within-site variation in the diversity and composition of aboveground vegetation and seed bank in intensively managed wet grasslands of north-western Germany, comparing field edges, field margins and field interiors. We tested the hypothesis that unfertilized buffer strips at field edges function as refugia of characteristic species even in grasslands that are managed intensively for silage production. In 55 grassland sites on each marsh and moor soils, respectively, we conducted vegetation surveys, seed bank analyses and soil chemical measurements in field edge, margin and interior plots, and searched for the factors causing within-site variation in vegetation composition. The total species pool was small at the 110 sites, i.e. 148 species in the aboveground vegetation and 107 species in the seed bank, demonstrating severe impoverishment. The α-diversity decreased from 23 species (median) per 200 m² at the edge to 15 species in the interior, with 38 species occurring only at field edges. The number of species with conservation value was very low in aboveground vegetation and seed bank and was only slightly higher at the edge than in the interior. Soil P availability was ca. 30% lower at the unfertilized edges than in the interior. We conclude that unfertilized buffer strips at grassland edges may help reducing nutrient leaching from high-input grassland systems, but they have mostly lost their refugial function for phytodiversity after decades of intensive management. Restoration efforts with seed or green hay transfer from richer source habitats are needed to promote biodiversity in field-edge buffer strips.