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134 BENGT PETTERSSONFig. 3. The great alva1· of Oland was formerly used aspasture for domestic animals, especially horses, whichkept· the landscape open and free from trees, thus favouringspecies that are weak in competition. Large parts of thealvar, however, are devoid of both trees and shrubsirrespective of grazing. The photograph shows an areawith fissures, being a transition between drainageless andkarst alvar. Oland, Vicldeby. June 14, 1947. Photo BengtPettersson.The calcicolous vegetation of the Pinus silvestriswoods on limestone on Gotland shows a rich variation.Among the forest types on this island thathave slight or no equivalences on bland twoprincipal kinds ought to be mentioned. Arctostaphylosuva-ursi pinewood of a very peculiar structureis most characteristic of North Got land (cf.HESSELMAN 1908b, Du RrETZ 1925 b), and theherb-rich pinewoods ("pineta herbida") occupylarge areas (cf. SERNANDER 1894, HESSELMAN1908b, Du RIETZ 1925 b) and seem to have gottheir present appearance as a result of continuousclearance and grazing.The meadowlandThe thinly wooded meadows once so characteristicof Gotland (cf. RYBERG 1948) and stillremaining in places as groves, thickets or openpastures have always had a smaller extension onbland, though several fragments of such vegetationare still left there. These wooded meadowshave nearly always been connected with moistmeadow and fen vegetation as is shown by meansof land-surveyors' maps from the 17th to the 19thcentury and by their present remains in the landscape(BENGT PETTERSSON 1955, map p. 64).The importance of woody vegetation in the mead-ows has been a little exaggerated. However, it cannot be denied that several woody plants have beenused in ancient rural economy and thereforefavoured in the meadowland. It is evident thatthese trees and bushes have earlier occurred ingreater abundance. Many kinds of meadowlandare apparently derived from the deciduous forestthat covered a great deal of the ground before plantand animal husbandry were introduced in the Neolithictime. But the composition of the presentwoody vegetation in the meadowland is by nomeans identical with pre-Neolithic conditions.Through the cultivation the hydrology has certainlyalso been changed. Moreover, deciduousvegetation is now spreading over areas which havebeen abandoned by culture.The flora: Some facts and problemsThe flora of Oland and Gotland is on the wholeof a South-Swedish character. However, severalspecies comon on the Swedish mainland are lackingboth on Oland and Gotland, the negative featuresbeing more pronounced regarding Gotland.Both islands contain about the same number ofvascular plants (ea. 1050 species, cf. STERNER 1938,1948, p. 95, BENGT PETTERSSON 1945, p. 40). Thefloras of the islands are closely related but notidentical. The cryptogamous flora and vegetation·of the islands although eagerly studied by manyworkers have never been subject to a full inventory,but the main features and the peculiaritiesare well known.The marked floristic difference between Gotlandand bland that was early pointed out by K.JOHANSSON (1897) and later by KUPFFER (1925)gives rise to several interesting problems. blandhas in some disjunct native species a close connectionwith the steppe vegetation of South-EasternEurope, e.g. Plantago tenuiflora (STERNER 1922),Artemisia oelandica (WENDELBERGER 1960), andRanunculus illyricus (STERNER 1938), while Gotlandhas several species joining its flora to themountain flora of the southern parts of the continent:Oalamagrostis varia (cf. NYGREN 1946),Orchis Spitzelii (BENGT PETTERSSON 1940, 1958), andother species, all probably of Late-glacial age. Thesame statement is valid for Sanguisorba officinalisActa Phytogeog1-. Suec. 50