DISPERSAL, GERMINATION AND EARLY ESTABLISHMENT OF HALOPHYTES AND GLYCOPHYTES ON A GRAZED AND ABANDONED SALT‐MARSH GRADIENT

S ummary In a study of an abandoned salt‐marsh on Schiermonnikoog in the Netherlands, including an area where cattle grazing had been resumed, it was discovered that upper salt‐marsh and dune species did not spread to the lower salt‐marsh. Glass‐house experiments, carried out on germination and dry matter production under increasing salinities, suggested that the high salinity of the lower salt‐marsh was an important factor. On a grazed area of formerly abandoned salt‐marsh, lower salt‐marsh species spread to the upper salt‐marsh and dune. This could be partly due to the better germination of lower salt‐marsh species than upper salt‐marsh and dune species, since the salinity of the uppermost cm was higher temporarily and locally in the grazed than in the abandoned salt‐marsh. The canopy structure determining the amount of light reaching the soil also seemed to be an important factor enabling lower salt‐marsh species to spread. In experiments, in which seeds of different taxa were sown into vegetation, lower salt‐marsh species became established, particularly in the grazed area. The results of glass‐house experiments, on germination and dry matter production under a range of light intensities, were consistent with studies of early establishment in upper salt‐marsh and dune species in both the grazed and abandoned areas. Tidal seed dispersal resulted in the occurrence of lower salt‐marsh species in the seed bank and seedling populations in the low and open canopy of the grazed upper salt‐marsh and dune. Seed transport by cattle and geese could be important in the dispersal of some halophytes of the lower salt‐marsh.