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190 FOLKE BJORKBACKEffects of ditchingThere have been attempts to ditch the Algfloarna,like many other large mires in Norrland,but these efforts have given a very modest economicreturn, to put it mildly. This is partly dueto ineffective ditch systems, partly to deficiencyin certain nutrients (most usually P and K). Withmodern mechanized methods, labour costs are reduced,draining effectivity is highly increased, andthe application of fertilizers on a large scale is nolonger out of question. It is therefore absolutelynecessary to take measures in time to place someexamples of the large Jamtland mires under conservation,before ditching will be taken up againon a large scale despite the discouraging results ofolder enterprises.The ditching on Algfloarna was made in thebeginning of this century. Its efficacy was differentin various parts of the mire complex due mainly tovariable gradients. Some interesting after-effects onvegetation may be mentioned. Where a high-hummocky"rib" ("string") was cut through, a numberof Trichophorum caespitosum tussocks have filledthe gap, almost re-stabilizing the hydrography..Part of a ditch has been filled in by a growth ofOarex chordorrhiza and Equisetum fluviatile (bottomlayer of Scorpidium scorpioides) which althoughquaking is more traversable than the "flark" areason either side of the former ditch.A common change at drained edges of fen surfacesis the invasion of Polytrichum spp. into lowhummock communities earlier formed by Sphagnumwarnstorfianum, a succession Tomentypnetum---.:;..Polytrichetum in the terms of Du RIETZ (1949a).Polytrichum may even colonize the flarks, where itmay join strange combinations such as a Oarexlivida-Polytrichum affine society. Another mosslocally favoured by partial drainage is Sphagnumplumulosum which in some flarks has expanded aswide swelling mats occasionally even overwhelmingyoung seedlings of pine.Vegetation of AlgfloarnaThe mire complex consists of three kinds ofhydro-topographical mire elements (SJ6RS 1948a,Ch. 3), viz. bog, mixed mire, and various kinds offen elements. Elements of ombrotrophic bog orpoor fen singly or in combination (see below) markthe position of the water divide; mixed mire of theribbed type occupies the central, flat, open expansesof the complex; and areas of fen elements arefound close to the small hills of mineral soil wheresoligenous water rich in electrolytes enters the mire.Boa ELEMENTS.-In many mires in South Swedenthe boundary between bog and fen is a sharpline of demarcation-the mineral soil water limitof THUNM.ARK (1940), the fen plant limit of SJORS(1946) or the limit of mineral soil water indicators(Du RIETZ 1954b). In North Swedish mire complexeswith their often complicated hydro-topography,this line may be diffuse and consequently difficultiesarise to keep bog and fen areas apart. Largeareas may have a bottom layer of the same bryophytesas the bogs, but in the field layer scatteredfen indicators occur such as Oarex pauciflora orC. rostrata. Analogous conditions occur in hummocksof Sphagnum fuscum occurring as "islets"or "strings" in mixed mire. These hummocks containvarious fen plants rooting below the fuscumcushions in peat that has not yet been so stronglymeiotrophified (regarding the general phenomenonof meiotrophy see INGM.AR 1963). ACKENHEIL (1944)regarded these communities as a kind of hybridsociations, with an ombrotrophic bottom layer anda (partly) minerotrophic field layer (see furtherDu RrETZ 1949a, p. 298).On the Algfloarna complex (and in several othermires in central Jamtland) quite extensive purelyombrotrophic bog areas do occur, however, andeven make up important parts of the complexes.According to the material available, two types ofbog elements have been discerned.One type consists of bogs sloping unilaterallyfrom the water divide, and having low, treelessridges ("ribs", "strings") built up by Sphagnumfuscum. Important species of this Betula nana­Rubus chamaemorus-Sphagnum fuscum associationareA ndromeda polijoliaBetula nanaEmpetrum hermaphroditumRubus chamaemorusEriophorum vaginatumSphagnum fuscumSphagnum parvifolium.Acta Phytogeog1·. Sttec. 50