CHAP. LI LICHEN-TUNDRA OR LICHEN-HEATH 209 



fells (plateaux) of Norway, for instance between Gudbrandsdalen and 

 (Esterdal, on the Faroe Isles, ^ Iceland, and Lappmark and Siberia. In 

 Greenland they are only scantily and feebly developed, in fact, typically 

 only in the interior of the south, where they may cover extensive tracts, 

 and consist especially of Stereocaulon alpinum and Cladonia rangiferina.'^ 

 In Antarctic lands lichen-heath, with Neuropogon Taylori, appears to 

 occur on the higher mountains of Kerguelen,^ and occurs in South Georgia 

 with Sphaerophorus, Stereocaulon magellanicum, Neuropogon melaxan- 

 thus, and Sticta Freycinetii.* 



Between the hchens one finds, in the Northern Hemisphere, Empetrum, 

 Betula nana, Loiseleuria procumbens and other Ericaceae, Juniperus 

 communis, and other creeping low shrubs and dwarf-shrubs. Various 

 lierbs occur sparsely scattered in this carpet, just as in moss-heath, includ- 

 ing species of Lycopodium, Carex, Hieracium, Deschampsia flexuosa, 

 Nardus stricta, J uncus trifidus ; mosses are present also. Both dwarf- 

 shrubs and herbs are xeromorphic, and the species are the same as in 

 the adjoining fell-fields ; they usually remain humble and more or less 

 concealed within the carpet of lichen. The causes for the xeromorphy 

 may be the same as in the case of moss-heath acidity and coldness 

 of soil, also wind. 



On the level or undulating tundra-plains of northern Europe, which 

 are swept clear of snow by storms in winter, fruticose lichens succeed 

 but ill. Here crustaceous lichens preponderate, and Lecanora tartarea 

 becomes extremely widespread, for instance on heaths in Lapland, covering 

 with a brittle incrustation the dense mat of the lichen-heath that has been 

 killed by dry winds ^; it also appears, though in smaller quantity, in 

 Greenland. In temperate zones lichen-heath occurs, but to no great 

 extent.^ 



When the dwarf-shrubs, Betula nana, Calluna vulgaris, Vaccinium 

 Myrtillus, V. uliginosum, and a few willows, become taller, there arises 

 a vegetation consisting of two storeys, and when the dwarf-shrubs 

 become more numerous lichen-heath passes over into dwarf-shrub 

 heath. 



FeU-field, moss-heath, and lichen-heath (merging into dwarf-shrub 

 heath) are distributed over most of the barren tracts in the far north 

 of Lapland, Siberia, North America (where they are known as ' barren 

 grounds '), Greenland, Spitzbergen, and Iceland, also at higher altitudes 

 on high mountains, and in Antarctic countries near the Straits of Magellan. 

 They certainly present to us a picture of the first vegetation that pre- 

 vailed in the North after the Glacial Epoch. Under more favourable 

 conditions they become associated with Sphagnum-moor and dwarf- 

 shrub heath.' 



' Ostenfeld, 19086. ' Rosenvinge, 1889; Hartz, 1895. 



' Schenck, 19056. ' Skottsberg, 1905. ' See p. 72; Kihlman, 1890. 



" Grabner, 1895 ; Warming, 1907-09. "' For the literature see p. 258. 



WARMING 



