250 SUCCESSION IN EURASIA. 



Ostenfeld (1908) has made a more or less successional classification of the 

 plant formations of the Faroes. The insular climate and irregular configu- 

 ration of the surface make it difficult to give a permanent account of the plant 

 associations, as they merge gradually into each other and are liable to frequent 

 changes. Most of them, moreover, are closely related and are distinguished 

 by small differences which are often variable: 

 A. Natural formations. 



1. Halophile formations. 



a. The sand-strand formation; Hondkenya association, Elymus association. 



b. The sand-dune formation; Psamma association. 



c. The aalt-marsh formation; Atropis association, Carex salina association, 



Plantago maritima association. 



2. Subalpine formations. 



a. The plankton formation. 



6. The fresh-water lithophyte formation; Cladophora association, Entero- 

 morpha association. 



c. The linmse formation of the lakes; Litorella association, Sparganium- 



PotamogeUm association. 



d. The Umnse formation of running water. 



e. The hydrophyte formation aroimd springs and streamlets; Philcmotis 



association, amphibious association. 

 /. The swamp formation; Heleocharis association, Menyanthes association. 

 g. The moor formation; boggy sedge-moor association {Cyperaceae-Sphag- 



num association), grass-moor association {Glumifior-Hylocomium 



association) with Nardus facies, Juncus sqiiarrosus f acies, and Scirpua 



caeapitosus facies. 

 h. The heather-moor formation (moist CaUuna heath); CaUurup-Erica 



cinerea association. 

 i. The grass-slope formation; Carex binervis-Lmvla sUvatica association, 



Anthoxanthumr-Agrostis vulgaris association, with Agroslia vvlgarU 



facies and Anthoxanthum facies. 

 j. The cliff vegetation; the lithophyte formation; the typical chomophyte 



formation; the ombrophile chomophyte formation; the thermo- 



phile-chomophyte formation. 



3. Alpine formations. 



o. The rocky-flat formation. 



6. The alpine-bog formation; Eriopharum^Carex pidla association. 



c. The Grimmia heath formation. 



c*. Transition from Grimmia heath to grass-moor (transition formation). 



4. The vegetation of the sea-fowl cliffs. 



BRITAIN. 



Smith (1903) has reached the conclusion that heather has arisen from forest 

 in Scotland in many cases, as suggested by the agreement in their limits. He 

 seems to incline to the view that this is primarily the result of deforestation, 

 due either to limabering or to disturbance of existing conditions of drainage. 

 Forests or other vegetation may also be destroyed by wind-bome sand, or by 

 the regular burning of grouse-moors resulting in the development of heath. 

 Slopes ( 1903) has described the colonization of the exposed muddy bed of a river : 

 After 4 to 6 months. Ranunculus aquatilis and Lemna minor were the only 

 true aquatic relicts, while Juncus, Nasturtium, Scrophularia, etc., had appeared 

 in almost pure patches of seedlings. A year later, a considerable number of 

 species had invaded from the land, and 5 had formed dominant communities. 

 By the end of 1902, Alisma plantago and Ranunculus aquatilis had disappeared, 

 and by 1903 only 3 amphibious plants, Glyceria aquatica, Phragmites, and 

 Scrophularia aquatica, remained in any quantity. 



