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Micro-Vegetation of a MireBy TOM FLENSBURGThe microscopic algae of fen and bog waters formtheir own communities, more or less analogous tothose made up by macrophytes in the same environments.In the algal vegetation, too, there is a greatdifference between the richer parts of a mire,strongly influencėd by mineral soil water, the partsthat are less rich but still minerotrophic, and theombrotrophic bog with its extreme deficiency innutrients due to the total absence of access ofwater from mineral soil (Du RrETZ, e.g. l949a,l954b). To illustrate the chemical difference, it canbe mentioned that in minerotrophic shallow lakes orpools on a mire, of the type dealt with below, pHis frequently of the order of 6 to 7, while on theopen central area of an ombrotrophic bog, valuesbetween 3.5 and 4 are often found. There are similardifferences in other chemical factors, and also differencesdue to a variable supply of water. As aconsequence, the microphyte communities arehighly different in the various parts of a mire.As an example material will be used from investigationsmade within the Store Mosse complex,including Lake Kavsjon. This mire is situated northof Varnamo, in the west-central upland of the provinceof SmaJand. With its nearly lOO sq. km it isthe most extensive mire in South Sweden. Thelarge extension of mire in this district is due to afairly high annual precipitation (about 700 mm)and a level topography. Fortunately, in its centralparts the mire is not damaged by human interference,a prerequisite for a profitable study, forditching would have drained the natural pools andother shallow bodies of water on the mire andspoilt their micro-vegetation. The drainage of LakeKavsjon, on the other hand, was first favourableto most algae (see below). Micro-vegetation similarto that of Store Mosse, but not always so welldeveloped, is known to occur in other South Swedishmires (THUNMARK 1942, Du RrETZ l949a,l950a, b, C, 1954b, l959a and b, FETZMANN 1961,FLENSBURG, unpublished).The richest algal community was found in LakeKavsjon. This is a shallow body of water, nowheredeeper than 2 m, and got its present characterthrough partial drainage carried out in the year1840, according to OsvALD (l925 a). A considerablepart of the original lake surface was retained. Verylikely, the rich algal vegetation developed afterthis lowering of the water level. The further developmentand present state is described in an as yetunpublished report by GoRAN SvENSSON. Unfortunatelyits future existence is threatened by furtherdrainage, which may even cause the openwater to disappear almost totally. The lake has atpresent an eutrophic character; pH is 6 to 7.There are certain differences between various partsof the lake, but in most parts the micro-vegetationis very rich in species. There are more than 300algal species, of which more than 200 are desmids.Nowhere in Sweden has so many microphytes beenrecorded from a community of limited extension.Most of the desmids are conspicuous, when observedunder the microscope, and some are easy tofind and identify. The genus Cosmarium is muchbetter represented in Kavsjon than in the mireitself. There are in all about 70 species, most ofwhich are exclusive to the comparatively nutrientrichKavsjon, as far as this mire complex is concerned.This is true both of typically benthic speciesand of a number of species which are found inplankton samples as well. Most of the Cosmariumspecies are absent from Kalvsjon, a small adjacentlake with a lower content of electrolytes; however,the large 0. ovale, a species characteristic of lakes,is found in Kalvsjon as well.The crescent-shaped desmids of the genus Closte.Acta Phytogeogr. Suec. 50