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234 GUNNAR WASSENFig. I. Shore of Lake Gardiken, Oarex juncella belt. Fullycovering bottom layer of hepatics, the dominant beingOephaloziella arctica. Right, glistering from moisture,a coating of Scytonema and other cyanophytes. Leftnumerous Preissia quadrata thalli and small shoots ofAgrostis stolonifera. After thaw but before high-waters,this belt enjoyed a very short period of exposure; it wasre-exposed about the end of July. May 15, 1962. PhotoG. Wassen.belt passes gradually (and usually without a welldefinedlimit) into the mountain birchwood orsubalpine belt" (transl. ).Before the damming was a fact in 1962, an inspectionin the beginning of May, when the extreme lowwaterstill prevailed, would reveal high geolittoralslopes, occasionally even wide flats or terracesstill above the level of the lake. Only a monthlater, the water level might have risen over fivemetres (the maximum amplitude being 5.69 m).The lake water then almost regularly but for ashort period inundated part of the surroundingforested area, the highest level shown approximatelyby the lowermost occurrences of V accinium myrtillus.A remarkable mixture of plants typical of low-land and mountainous areas was fou:rid on theshores. The prevailing habitat factors on the shoresshowed a certain parallelism with common featuresof the alpine environment: full insolation, abundanceof soil water, absence or scarcity of stronglyacid humus deposits, intense frost action and areduced growth period, on the shore due to submergence,on the mountain to long-lasting snowcover. These conditions gave some alpine plants,dependent on open soil or on moderate competition,a chance to grow between more usual shore plants(cf. SELANDER 1950a).The large amplitude in water level combinedwith weakly sloping shores and the shifting developmentof the substratum were important conditionsfor the impressive vegetational zonation. The mostcommon type of shore was almost covered byboulders. At the low-water's edge there wasusually a barricade of boulders formed throughpressure from the winter ice. This lowermost partof the shore was devoid of vascular plants butcovered by a thin film of cyanophytes. Above thispart followed consecutive belts characterized bySubularia aquatica, by Oarex juncella and by Call unavulgaris. Finally the uppermost, generally woodedpart of the geolittoral was characterized by V acciniumvitis-idaea, whereas V. myrtillus was absent,as previously mentioned.A tall shrub layer of Alnus incana was generallyfound in the upper part of the Oalluna belt, in frontof the forest fringe, and low, scattered Salix shrubgrew on the lakeward side of the alder thicket.The field layer was sparse and open, particularly inthe lower belts. A bottom layer of mosses and liverwartsshowed a parallel zonation. Although discontinuous,this bottom layer was rich in interestingspecies (see below).Typical species of the Subularia belt were Subulariaaquatica, Ranunculus reptans, Veronica scutellataand Alopecurus aequalis. The Subularia vegetationis an example of what SERNANDER (SET1926, p. 492; cf. 1918) distinguished as the "mudsprout"(iivjebrodd) formation, i.e. a low growthof small amphibious rosette plants inhabitingmuddy surfaces. Subularia, an annual species, aswell as Ranunculus and Veronica, ascended intothe next belt, the Juncella belt, where not onlyActa Phytogeog1·. Stec. 50