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Salt Marsh '' egetation In Southern SwedenBy VILHELM GILL NERIntroductionThe shore forms a transitional zone between landand sea, and its lower parts, the hydrolittoral, harboursa vegetation submerged at frequent and sometimeslengthy intervals and thus ·exposed to theactivity of the water. The more elevated parts, thegeolittoral, are out of reach for longer periods andthe highest strip is only occasionally and brieflytouched by high water, or on exposed shores, bywaves during landward gales.Of great importance to the composition of thelittoral flora is the range of the water level, whichdetermines the zonal distribution of the vegetation:.This can easily be observed at the seashore as wellas on the water-lapped edge of a lake. Anotherimportant environmental factor on the seashore issqil salinity, which is partly determined by variationsin the water level. The latter as well as thedegree of humidity it produces and soil salinity arethe p:-:-imary environmental factors responsible forthe composition of the seashore vegetation. An additionalsecondary influence is that of man's activitiesin the form of grazing and mowing. This especiallyaffects the true salt marsh, i.e. the meadowlikevegetation found in the geolittoral on fairlyfine-grained soil. This type of influence further includesthe removal of seaweed and drift.In the present paper the salt marsh is rathernarrowly defined to include only the plant life ofthe geolittoral zone. The terrestrial meadow immediatelyabove and the hydrolittoral immediatelybelow this belt are considered and briefly discussedas contact vegetation.Three different parts of Sweden figure in theaccount below. First the salt marsh vegetation ofthe West Coast is described and compared with thesalt marsh farther south, on the Oresund. Finallythe composition of the brackish meadow vegetationalong the East Coast south of and within the Kalmarsundarea is briefly touched upon. Farthernorthwards the marshes become increasingly likefreshwater ones, but some marine species occur allaround the Gulf of Bothnia.The West Coast, habitat factorsWATER LEVEL.---:-On the West Coast of Swedenthe variation in the water level of the sea is mainlydue to changes in wind direction and air pressure.It is greatest during the winter half year, when thehighest and lowest values are noted. Even on a shelteredsalt marsh the range can be up to 150-170 cm,and in the course of 24 hours the difference betweenthe highest and lowest levels can exceed a metre.In summer the range is rarely more than 70-80 cm,but nevertheless these non-periodic variations areniore significant than the tides. The latter are moreeasily observed on calm days. In the northern part .of the West Coast the tidal range is about 30 cm,in the southern parts barely half as great. On theOresund and the East Coast there is hardly any tideat all. Nevertheless the water level varies considerably,and as a result the littoral belt is much widerthan could be expected from tidal data only. Theline between the hydro- and geolittoral more or lesscoincides with the mean annual water level (GILL­NER 1952, 1960).SALINITY.-On the West Coast the surface wateris quite obviously still influenced by the brackishwater of the Baltic. This is of course mixed withsalt water as it flows in a broad current, the Balticcurrent, along the coast. Thus the salinity of thesurface water increases from Kattegat towardsSkagerrak as it mingles with deeper, more salineActa Phytogeog.r. Suec. 50