fulltext - DiVA

Lost and living lakes in the upper U me valley 239raxacum crocodes. This southern part of the lakeis dissected by a multitude of low morainic ridges,forming capes and small islands with interveninginlets and sounds. Each of the ridges has a northwestern,nearly treeless windward front and asouth-eastern leeward side with birchwood andbotanical indications of snow accumulation. Thezonation on the windward side shows an ecologicalinfluence from absence of snow, abrasion by thewind and heavy frost action, affecting the scantyheath vegetation above and less so the meadowlikevegetation below the high-water mark. Thoughhardly closed, the latter type of vegetation contrastsstrongly in its richness in species, but near the lowwater'sedge in late summer, the Carex juncella belthas only scattered plants (e.g. Carex saxatilis) betweenthe stones and the lowermost belt has someamphibious Caltha palustris and Alopecurus aequalis(Subula.ria being confined to sheltered bays withmuddy or silty bottoms).LAKE STORA UMEVATTNET.-The source lake ofthe main river branch, Lake Stora Umevattnet,had a unique position among Swedish mountainlakes, for multiplicity in edaphical conditions andfor richness in certain floristic respects, notably incryptogams such as mosses, liverworts and lichens.The damming of this lake, an accomplished fact in1965, is one of the great sacrifices forced upon natureby the technical development. We regret the lossof shore fens framed by sandbanks, deltas of brooksspangled by flowers of mountain plants, colourfulLotus corniculatus meadows below sediment terraces,shallow lagoons rich in water plants and Charafragilis bottoms where char and trout fed on copiousGammarus amphipods. Above all, we regret the lossof the peculiar vegetation on the rocky shores.Boulder shores, at the south-eastern end, showeda Calluna belt with restricted occurrence of Calluna,at its north-westernmost occurrences along themain river-course, but mountain species such asCassiope hypnoides and Salix herbacea, and alsoV accinium uliginosum dominated. In the centraland western parts of the lake, the high-water markwas mostly a horizontal demarcation line betweena thick humus carpet carrying birch wood vegetationand seemingly naked rock. A closer examinationrevealed occasional chasmophytes and of course,the littoral lichen cover, including a rich assemblyof little-known species especially where the rock waslimestone.Like Tarnasjon, La.ke St. Umevattnet had anarchipelago, but this was very different, beinglargely rocky, with both limestone and less cacareousrocks well represented. Calcicolous or calciclinespecies such as Oar ex rupestris, Chamorchis alpina,Draba nivalis, Kobresia myosuroides, Primulascandinavica and Sedum acre (western here) hadtheir main homes on the low skerries, now more orless washed over by the waves on the raised surfaceof the stormy lake. Woodless skerries, with a rug ofRhacomitrium lanuginosum on their hog's-backs,could show contrasting types of vegetation, evenside by side. Empetrum hermaphroditum vegetation,poor in species and growing on acid humus, alternatedwith Dryas mats containing several orchids,whereas a rich mixed vegetation including fen andmeadow species grew on the frequently soakededge of soil next to the high-water mark. Besidethe crustaceous lichen mono-layer on the rockitself, small calcicolous soil lichens of great geebotanicalinterest were recorded, such as Fulgensiabracteata, Lecidea decipiens, Toninia coerulonigricans,and also the common creeping Thamnoliavermicularis, many mosses, etc.Occasionally steep cliffs rose ten to twenty metresabove the original water-level and it is possiblethat some of the botanical treasures (also includingSaxifraga cotyledon) will survive in such localities,where they will escape inundation, for the raisingof the level is to be quite moderate. Nevertheless,we know from sad experience that a new littoralenvironment will never be formed below the futureartificial high-water mark, because the rhythmwill be reversed, with rising or maximum levelthroughout the summer, the period during whichthe naturally zoned communities need graduallysinking water. On the other hand the tapping to bemade in late winter gives no chance for an upwardspread of aquatic vegetation, and except for mobileor ephemeral beings the ecotone between lowestwater-level and land will mostly remain lifelessalong the eroded edges of the reservoirs.Acta Phytogeog1·. Suec. 50