fulltext - DiVA

The Borderland 173level, much of the distribution details may becaused by other factors than climate.SOUTH-EASTERN PLANTS.-Among the categoryof southern continental species that in Swedenshow a markedly south-eastern distribution, quite· a number touch or reach the eastern and middlesectors of the border zone (e.g. Laserpitium latifolium,H elianthemum nummularium, Trifolium montanumand Polygala comosa) and in some casespenetrate across it some distance. Thus Filipendulavulgaris, Seseli libanotis, Pulmonaria officinalis ssp.obscura, Phleum phleoides and a few others haveoutposts in Dalarna north-west of the oak-line. Allthese are practically absent from the west, as. faras the Swedish part of the border zone is concerned,but some of the eastern species go again farthernorth in eastern Norway (e.g. Filipendula vulgaris,Phleum phleoides, I nula salicina).SouTH-WESTERN PLANTs.-Some species with asouth-western distribution in Sweden reach theborder zone in its western part (e.g. Gentiana pneumonanthe,Radiola linoides). A few follow the borderzone itself towards the north-east while they areabsent (in this more eastern sector) both below andabove it. Examples are Potamogeton polygonifolius(ALMQUIST 1949a, p. 451) and Pedicularis silvatica(op. c., p. 449; but this species is frequent in Narke).Outpost localities of Erica tetralix in Varmland(HARD AV SEGERSTAD 1940, p. 12, 1952, p. 88,FRANSSON 1958, pp. 116-117), northern Vastmanland(MALMSTROM & J ONSSON 1954) and eastern Dalarna(ALMQUIST 1948, 1949a) fall in this peculiargroup too, the existence of which is an expressionof the fairly high humidity of the border zone.Along the major part of the border, there is amarked increase in humidity, and surely thisstrengthens the phytogeographical contrast.With respect to humidity, the border zone hasmuch in common with SW Sweden. The distributionof Trichophorum caespitosum, northern andwestern at the same time, illustrates this connection.In western Varmland and Dalsland, transitionalareas occur, e.g. the isolated upland area ofGlaskogen in SW Varmland (HARD AV SEGERSTAD1952, FRANSSON 1958, and in prep.) and elevatedparts of Dalsland (SJ6Rs 1953).NORTHERN PLANTS.-Finally the border zone isapproached, reached or overstepped by severalnorthern plants. ALMQUIST (1949a, p. 454) givesthe southernmost points of occurrence as far asDalarna is concerned (there are also a few in Vastmanlandand Varmland). Southern outposts of decidedlynorthern species are most common in westernDalarna. Some northern species have a widerdistribution, although markedly concentrated tothe elevated uplands and thus not reaching the oakline,e.g. Salix glauca, Epilobium Hornemanni, E.lactiflorum, Tofieldia pusilla, Sparganium hyperboreumand Lactuca alpina (M. FRIES 1948, 1949) .Spedes with their absolute southern limits near theoak-line are few (e.g. Viola Selkirkii, Phleum commutatum).To other northern plants, the border zone is onlya belt where they suffer a great reduction in frequency.They may overstep this zone with fewlocalities only (Carex disperma, C. juncella, C. aquatilis,Luzula sudetica) or have quite extensive occurrencesouth of it, as for example Betula nana,Carex loliacea, C. brunnescens, C. globularis, C. livida,J uncus stygius, PediculaTis sceptrum-carolinum,Selaginella selaginoides (ALEJ!iRTSON 1942 b), Alnusincana and Salix lapponum.CRYPTOGAMS.-The distribution areas of mostnon-vascular cryptogams are still not well knownenough to allow a similar treatment. A few southernmosses, e.g. Camptothecium lutescens, were mappedaccurately by V. KRUSENSTJERNA (1945 pp.162-170), although probably the material was notcomplete enough to give the precise position oftheir northern limits.Northern species are better known; thus Scapaniauliginosa (SJORS 1948a, p. 36, ARNELL 1956, p.197) halts in the upland above the border. Manybryophytes are members of the group with greatlyreduced frequency in the border zone but occurrencefarther south, e.g. Calliergon sarmentosum(ALBERTSON 1949), Sphagn1tm Lindbergii (SJORS1949 a), S. subfulvum (SJORS 1945), Drepanocladusbadius, Odontoschisma elongatum and others. ForActa Phytogcog.r. Suec. 50