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138 BENGT PETTERSSONFig. 7. Alvar (flat limestone ground)on a wind-swept low plateau closeto the sea. Lichens and moss cushionsdominate the vegetation onthe thin soil which is heavily affectedby frost upheaval. Scatteredjunipers grow in fissures. Rabbitshave just crossed the snow-drift.East Gotland, 6stergarn, Grogarnsberget.Jan. 30, 1962. PhotoBengt Pettersson.as argillaceous limestone strata crop out and havea less smooth surface than those on Oland, whichgenerally are extremely flat. On both islands humanactivities have created much of their present-dayappearance. This . influence comprises extensivegrazing by domestic animals, a devastation of woodand scrub that otherwise would spread over theparts that are provided with a deep soil layer orcriss-crossed by fissures. In certain cases there areevident traces of former cultivation. Over mostareas the human influence has diminished orceased during the last ·few decades, which hasresulted in immigration of woody plants and ofother species sensitive to grazing. Where the soilconsists of not too shallow moraine or gravel, manyformerly open areas of alvar have in this mannerbeen overgrown by thickets and brushwood.Oland has probably never had a grazing stock ofsheep which can be compared to that of Gotland,but the vast alvar areas on Oland have been grazedby other domestic animals, especially small horsesof a now extinct semi-wild breed. This grazingwas probably rather intense, but it was not localizedto fenced areas, the animals roaming _freelyin pasture outside meadows and arable land.During the last few years sheep of the domesticbreed of Gotland have been introduced to Oland,and their grazing has already profoundly affectedthe alvar vegetation over considerable areas .They commenced their grazing m a vegetationwhich was recovering after a long period of moderategrazing in ancient times. The recently introducedsheep are grazing in vast enclosures andtheir number is too great for the low natural productionof palatable plants. As a consequencethere has been bad over-grazing, and soil and vegetation,as it seems, are seriously damaged.We do not know exactly what the original grazingland of the alvar was like. Therefore, we have nopossibility to compare the actual situation withthat existing one or two centuries ago and cre::ttedby the grazing pressure during thousands of years.It is a well-known fact that several members ofthe alvar flora had greatly increased in frequencyand abundance in those areas where the grazingpressure had ceased or diminished during the lastcentury. This holds true both for Oland and Gotland.lnula ensifolia was long sought for in vain at alocality on Gotland discovered in the beginning ofthe 19th century and was thought to be exterminated,but it was rediscovered a hundred yearsafter its disclosure in exactly the same place. Itpresumably had endured the grazing pressure allthe time, probably growing as greatly reduced, inconspicuousspecimens (for it is very difficult toobserve all plants growing in intensely grazedvegetation; BENGT PETTERSSON 1958, p. 129-130)..Ac·ta Phytogeogr. Sueo. 50