SCANDINAVIA. 241 



Kellgren (1891) has described the invasions following the clearing of mixed 

 coniferous forest in Sweden: 



The typical pine-spruce formation passes into a Gi-Sphagnum formation 

 (Hult) in the valleys, and a pine-cladinosa-formation on the ridges. A severe 

 fire in such a forest destroys not only the pine and spruce, but also the moss 

 cover necessary for the reproduction of the fir. A birch or alder forest is 

 the result. After clearing, the moss cover is burnt only locally, and a number 

 of older trees are spared to serve as seed trees. Usually, in this case, a new 

 mixed coniferous forest again arises directly, while larger cleared areas are 

 open to grazing, and the grasses and sedges become more abundant, e. g., 

 Aira, Poa, Festuca, Carex, etc. 



Grevillius (1893) has described the development of vegetation on islands 

 which arose in Hjelmar Lake, owing to the lowering of the water-level in 1882 

 and again in 1886: 



The first stages had already been studied by Callm6 in 1887, four years 

 before the study made by the author. The number of species had increased 

 from 115 to 212. The increase was much greater on the islands produced by 

 the lowering in 1882, and upon those in the neighborhood of the shore or of 

 older islands. Of the 115 species in 1886, 23 had disappeared in 1892. The 

 new invaders were mostly strand plants, with some, especially ferns, from the 

 forest. In 1886 the species were common to only a few islands; in 1892 the 

 flora was much more uniform. At the earher date the soil was mostly still 

 bare, while later the number of individuals had greatly increased, and trees, 

 shrubs, and sedges had developed dense societies. Most of the island showed 

 a fairly continuous vegetative covering; distinct associations were present 

 only on islands a half meter or more above the water-level. The typical 

 formations were 3, arranged zonally as follows: (1) a strand association of 

 grasses, sedges, and herbs; (2) a zone of shrubs, mostly Salix, below which 

 grew small sand plants; (3) a central nucleus of dense young forest, mostly 

 of Betula verrucosa, Populus tremula, and Alnus glutinosa. Pines and spruces 

 had appeared sparingly on a few of the islands. 



Ortenblad (1894) has regarded as relict formations the societies of Ulrmis 

 montana, Tilia europaea, Acer platanoides, and Coryliis avellana found in the 

 province of Norrland, Sweden: 



These consist of 15 isolated and widely separated groups of little extent, 

 but of uniform habitat. The latter is warm, protected from cold winds, and 

 with rather stony dry soil. The causes of the disappearance of these groups 

 are found in climatic change and in the invasion and competition of the spruce. 



Grevillius (1895) has made a study of the development of vegetation on 

 islands of different ages in Sweden: 



The chief succession consists of the following stages: (1) an association of 

 Agrostis stolonifera and Heleocharis palustris in still water, with Alopecurus 

 geniculate, Carex aquatilis, C. ampuUacea, Equisetum limosum and Ranunculus 

 flammula; (2) on stretches above the water-level, Jumyus halticus, J. alpinus 

 Sdrpus silvaticus, Eriophorum angustifolium, Carex canescms, C. goodenaughii' 

 Eguisetum limosum, E. palustre, Deschampsia caespitosa, TriglocMn palustre 

 Galium palustre, Pedicularis palustris, Pamassia palustris, and Sagina nodosa 

 together with small plants of Salix pentandra and triandra, and more rarely 



