Density and richness of soil seed banks in loess grasslands

We studied the vegetation and seed banks in a Salvio-Festucetum loess grassland and in and formerly grazed and then abandoned Cynodonti-Poëtum loess pasture. We answered the following questions: (i) How dense are the local seed banks? (ii) Which species of the vegetation possess a seed bank? Soil samples were collected in early spring, 2010. Samples were concentrated and treated using the seedling emergence method. Percentage cover of vascular plants was recorded in twelve, 1-m2-sized plots in June, 2009. We found that the mean densities of seed banks were similar in both grassland types (20,200 seeds/m2 in Salvio-Festucetum and 22,800 seeds/m2 in Cynodonti-Poëtum, respectively). Altogether, 94 species were detected both in vegetation and seed banks. In the pasture the species-poor loess vegetation (a mean of 10.2 species/m2) was characterised by the high cover of Festuca rupicola (mean cover of 45%). Conversely, we detected significantly higher species richness in Salvio-Festucetum grassland (t-test; p< 0.001, mean, 27 species/m2). The seed bank was characterised by common forbs (Hypericum perforatum 6,200 seeds/m2, Galium verum 4,270 seeds/m2, Achillea collina 2,100 seeds/m2) and graminoid species (Poa angustifolia 1,060 seed/m2, Carex stenopylla and C. praecox 2,480 seeds/m2) in both grassland types. Dense seed banks were typical for Conyza canadensis (6,760 seeds/m2) and Veronica persica (1,215 seeds/m2). Most of the characteristic species of loess grasslands possessed only sparse seed banks (e.g. Salvia austriaca, S. nemorosa, Pimpinella saxifraga, Medicago falcata). Our results suggest that the seed bank can have only a limited role in maintaining species diversity in loess grasslands.