Seed banks of grazed and ungrazed Baltic seashore meadows

Abstract. The seed banks of three grazed and three ungrazed seashore meadows were studied on the west coast of Finland. 8486 seedlings (mean 13 669 seedlings/m²) germinated from cold-treated samples (n = 343; depth = 10 cm). Most seedlings and species were monocots and perennials. The seed bank flora included 54 dicots vs. 28 monocots and 66 perennials vs. 16 annuals. The most abundant species were Juncus gerardii, Schoenoplectus tabernaemontani, Eleocharis uniglumis, Agrostis stolonifera, Juncus bufonius and Carex nigra, which made up 73% of the seed bank. Numbers of species and seedlings differed between elevation classes. Species richness was highest in elevation class 50–70 cm. The highest seed density occurred in class 20–50 cm. A model for size and species composition of the seed bank in relation to elevation is presented. The seed bank was larger and richer in species in the ungrazed than in the grazed sites, but not so in the upper elevations and closest to the open sea. Grazing reduced the size of the seed bank of Agrostis stolonifera, A. capillaris, Calamagrostis stricta, Elymus repens, Juncus bufonius, Limosella aquatica and Schoenoplectus tabernaemontani, but increased that of J. gerardii. 32 species germinated only from ungrazed samples and 11 species only from grazed ones. Multivariate classification resulted in nine sample groups. The ordination scatter was best explained by the flooding stress variables, elevation, the distance from the water line and the number of helophyte species in samples. 75 species were found both in the seed bank and in the vegetation, but there was a significant lack of resemblance (in the Mantel test) due to over-representation of some species. Eight species occurring only in the seed bank were mainly annuals or biennials (63%); those occurring only in the established vegetation (86 species) were mainly perennials (86%).