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Gotland and Oland. Two limestone islands compared 133Fig. 2. Flat rocky ground withthin pinewood and juniper shrubis characteristic of Gotland. Bottomleft stratified crystalline limestone,only partially covered withmoss cushions (dominant Tortellatortuosa), to the right thinsoil produced by weathering, wetin winter and regularly dried upin summer, with a sparse vegetationof Festuca ovina and Hieraciumflor·entinum. In the backgrounda narrow strip of tallervegetation (Sesleria) conditionedby a rock fissure. North Got land,Hangvar, Ire. July ll, 1938. PhotoBengt Pettersson..folia, C. rubra, and Orchis Spitzelii (cf. op. c., p.77-82 and PI. V). It is remarkable that species of.a northern type of distribution in Scandinavia may.also have a similar trend, e.g. Draba incana andseveral bryophytes and lichens.The distribution of the southern calcicole Gypsophilafastigiata is on the whole concentrated tocoastal vegetation close to the sea on Gotland, butis distributed all over the Great Alvar on bland.On the other hand Anemone (Pulsatilla) patens'(sens. lat.), an eastern-Continental species growingin thin pinewood on Gotland, does not occur onOland, and avoids the maritime districts of Gotland(cf. BENGT PETTERSSON 1958, p. 105).Woody vegetationGotland may be characterized as a woodlandwhere pine forest predominates, but bland is inlarge parts an almost woodless land where, moreover,deciduous trees usually predominate in thescanty woody vegetation except for conifer foreston sand in the northernmost part. No more than11 % of the total area of bland is covered by woodsand half of these ll % consists of deciduous wood(STERNER 1948, p. 170). This is a fundamental differenceand may be explained by co-operatingclimatic, pedological and historical factors.It is interesting that on southernmost Gotlandgroves of deciduous trees, especially birch, play aprominent role in ancient meadowland and pastures.At the same time this is the most maritimepart of the island, and spruce wood has not grownthere in historic time which is said to be due tocertain effects of management, especially a considerablestock of sheep grazing in winter. Thesheep are now removed from most parts, andwoody vegetation is recolonizing open areas.STERNER (1926, 1948) has described the differenttypes of deciduous vegetation on bland (cf. SJ6-GREN 1964) and stressed the fact that most of thewoody vegetation has been developed under profoundhuman influence and that . it has greatlychanged during the last century.It is a curious fact that to the north both islandsend in areas where sandy deposits predominate,on bland the sandy district at Boda and on Gotlandthe Avanas on the island of Faro and the outlyingisland far north, Gotska Sand6n. The sandydeposits on these islands are derived substantiallyfrom submarine sands. The vegetation of thesesandy districts is of great affinity to vegetation ofsandy soil on the mainland: coniferous forest, purepine on North Gotland, mixed pine and spruce onNorth bland.Acta Phytogeog.r. Suec. 50