Effect of flooding and draw-down disturbance on germination from a seashore meadow seed bank

The objective of this study was to investigate the effects of flooding and draw-down on the germination from the coastal grassland seed banks and to determine whether the effect of flooding varies between the delta and the seashore. Seed bank samples were collected from three shore transects in SW Finland, two on the shore of the Baltic Sea and one on the delta of River Kokemaenjoki. Samples were germinated in non-flooded and flooded conditions for over a month. after which both treatments were maintained in non-flooded conditions, A total of 9267 seedlings of 47 species germinated and mean density of seeds in the soil was cu. 84 000/m(2). Most of the seedlings were monocots (98%) and perennials (98%). Ca. 30-40% of the species found in the above-ground vegetation had a seed bank including the majority of the most abundant species. The number of seeds and species richness increased as the organic layer became thicker. The organic layer was thicker in the seashore samples and the seed bank was significantly larger than in the delta. The flooding and draw-down treatment significantly increased the number of germinating seedlings in the seashore and also increased species richness in two transects, one in the delta and the other in the seashore. Two species. Schoenoplectus tabernaemontani and Typha latifolia, had significantly higher germination in the flooded treatment than in the non-flooded. Apparently, many species in these coastal grasslands have adapted to flood disturbance and for seeds of some species flooding may work as a positive signal, possibly breaking dormancy.