SCANDINAVIA. 243 



type is still poorer, and through a disturbance in drainage it is often converted 

 into swamp forest. The latter reproduces practically not at all and must 

 eventually develop into a treeless formation. The behavior of the different 

 types towards fire is determined by the density, the pine heath suffering least, 

 the spruce forest the most. In general, the effect of a fire is to bring about 

 the establishment of a type which has preceded by one or two stages. In 

 regions where the birch is abundant it invades burns readily and is rapidly 

 foUowed by conifers. Where the birch is sparse or lacking, the succession 

 is slower, but the pines appear sooner or later. 



Warming (1895) has probably had the largest share in the development of 

 successional studies in Scandinavia, and perhaps elsewhere as well. In addi- 

 tion to his investigation of succession in the marshes and on the strands and 

 dunes of Denmark (1890, 1891, 1894), he summarized the results of his own 

 researches and those of other European students in the several editions of his 

 handbook of ecology (1895, 1896, 1909). The extent of this work makes an 

 adequate account of it impossible here. In addition to the several papers 

 abstracted in this chapter or discussed elsewhere, the student of strand and 

 dune seres in particular will find his "Strand Vegetation" and "Dimes" com- 

 prehensive and invaluable. 



Petersen (1896) has studied the vegetation of "Lille VUdmose" in northern 

 Jutland, one of the moors mentioned by Steenstrup : 



Its chief interest lies in the striking miiformity of the vegetation, or rather 

 in the uniform mixture of the species with different successional relations. 

 The marginal zone consists of typical moor plants as well as species from drier 

 habitats. Here are to be found: 



Juniperus communis. Salix aurita. Empetrum. nigrum. 



Anthoxanthum odoratum. S. repens. Erica tetralix. 



Airaflexuosa. Belida odorata. Calluna vulgaris. 



A. caespitosa. Myrica gale. Andromeda polifolia. 



Carex vulgaris. Rubus chamaemorus. Oxycoccus pahtstris. 

 Juncus lamprocarpus. 



The central area is dominated by Calluna vulgaris and Eriophorum va^ina- 

 tum particularly, together with Sphagnum and Cladonia rangiferina. The 

 following are frequent: Erica tetralix, Andromeda polifolia, Oxycoccus palus- 

 tris, Rvbus chamaemorus, and Eriophorum angustifolium; Empetrum nigrum, 

 Drosera, Sdrpus caespitosus, and Rhynchospora alba are found sparsely 

 throughout. 



Hemmendorff (1897) has traced the development of the fresh-water vege- 

 tation of the island of Oland in Sweden, as is indicated in the sequence 

 shown in figure 10: 



Woodland 



I 



Rhamnus frangula formation 



Myrica gale form. 

 Molinia coerulea form. 



Cladium mariscus form....^ ^Schoemjs form. 



Phragmitesform. 

 Aquatic vegetatiotv. 

 Fig. 10. — Hydrosere in the island of Oland, Sweden. After Hemmendorff. 



