fulltext - DiVA

98 VILHELM GILLNERlayers. (Regarding salinity see further W lERN's essayin this volume.) Owing to the special hydrographicconditions on the West Coast the salinityof the sea is subject to rapid variations. On theKattegat coast (off central Halland) the averageis 20-22%0, on the Skagerrak coast (off centralBohuslan) 28-30 %o· At the Vinga lightship W. ofGoteborg the salinity of th e surface water variedbetween 15.6%0 and 32.6%0 in the course of a year.Of special interest in the present context is thesalinity of the water in bays and firths. Here thesea receives fresh water from outflowing inland .watercourses. This gives rise to still greater variationsin the salinity including values as low as thosenormally found along the Baltic shores.LAND UPHEAVAL.-A final important habitatfactor is the land upheaval, which is considerableboth on the West and East Coasts but negligible inthe south.Vegetation of West Coast marshesAgainst the environmental background thusbriefly sketched, I shall now try to describe the saltmarsh vegetation of the West Coast (previouslypresented in GILLNER 1944, 1950, 1960. See alsoDAHL & HADAC 1941, regarding a part of theadjacent Norwegian coast.) In this part of thecountry topographical conditions do not favoursalt marshes. In Halland sandy beaches predominate,while Bohuslan has mainly rocky shores. Inthese two provinces the salt marshes are restrictedto a few sheltered, shallow beaches and the innerparts of firths and bays.MARSHES OF NORMAL SALINITY.-0n distinctlysaline salt marshes not influenced by outflows offresh or brackish water Puccinellia maritima dominatesthe lower geolittoral. This vegetation formsthe well defined plant association Puccinellietummaritimae, which is part of the alliance Puccinellionmaritimae. Other species faithful to this associationare Spergula marginata and H alimione pedunculata:Also present are Spergula salina, Aster tripolium,Triglochin maritimum, Plantago maritima, Glauxmaritima, occasionally Limonium humile. The vegetationis closed and characterized by several fleshyspecies. Locally Plantago maritima may be prominentand reach a size of several dm. The ground isalways moist, and the community often flooded,especially towards the end of the vegetation periodwhen the mean water level has started rising. Inconsequence the soil surface is usually covered byalgae among which Vaucheria species are conspicuous.A Puccinellietum distantis occurs in patches oneroded or trodden ground.Towards the sea the Puccinellietum is borderedby a sparse hydrolittoral growth of Salicornietumstrictae. A faithful member of this is the glasswort,Salicornia stricta, which is frequently the only vascularplant. The soil cover is made up of cyanophytesand diatoms. The community demands asheltered shore, and under favourable conditionsmay have a vertical distribution of 15-20 cm. It iswithin almost constant reach of the sea, and evenon fine summer days at rather low water levels itmay be flooded, at least at high water. The ·openvegetation in Salicornietum strictae and the closedone in Puccinellietum maritimae are distinctly demarcatedfrom each other.Regarding soil ecology, this seems to be relatedto excessive wetness causing oxygen deficiency, forthe steadily repeated, protracted flooding of thehydrolittoral implies poor aeration of the soil. Thisprevents Puccinellia maritima from colonization.The pioneer species Salicornia stricta is less demandingin this respect, and its root activity improvessoil aeration. By reducing the movements of thewater the vegetation cover further increases sedimentationand encourages the formation of a top.soil suitable to the actual salt marsh vegetation.On the landward side of the Puccinellietum maritimae,in the central and upper geolittoral, theassociation Juncetum Gerardi is found. A speciesthat strongly prefers this community is JuncusGerardi. Especially in the early aestival aspect ofthe salt marsh Armeria maritima is conspicuous inthe upper geolittoral on substrates containing ahigh proportion of sand. Like Car ex distans, Lotustenuis, Odontites litoralis, Agrostis stolonifera andFestuca rubra (the two last-named almost certainlyin special ecotypes), Armeria maritima indicatesthat the association Juncetum Gerardi belongs tothe alliance Armerion maritimae. The communi-Acta Phytogeogr. Suec. 50