THE DEVELOPMENT OF COMMUNITIES 309 



Soil bacteria and algae usually appear as the first plant community. 

 Microcoleus chtho7ioplastes and Lyngbya aestuarii, as first invaders of 

 dry salt marshes about the Mediterranean, form an algal crust before 

 any seed plants gain a foothold. Similarly, Zygogonium ericetorum 

 forms a thick, fibrous cover on the acid soil of fresh-water swamps. 

 According to Treub, blue-green algae were the first plants to cover 

 the naked slopes of pumice and ash on the island of Krakatao with a 

 dark-green gelatinous coating. 



Upon stumps there soon appears a luxuriant multiform saprophytic 

 vegetation of low fungi and bacteria. On stumps of deciduous trees in 

 southern Finland this initial stage includes species of Endomyces, 

 Sacchar amy codes, Fusarium, Mucor, and Oidium forming a distinct 

 association. Later, algae such as Nostoc and Chlorococcus appear 

 and are soon followed by scattered mosses and algae, forming the 

 Cladonia hotrytis-P annelia furfuracea associsiiion (Krohn, 1924). 



According to Van Oye (1924), the succession of epiphytes on the 

 Javanese forest trees comprises three stages. There is first a pioneer 

 association of Myxophyceae and Trentepohlia. This is followed by 

 mosses, Drymoglossum and various Polypodiaceae, leading to the 

 climax epiphytic association of ferns and orchids. 



Lichens often come in first on resistant substrata, such as the bark 

 of trees, wood, rock, gravel, and sand. Therophytes are pioneers on 

 warm, porous soils of arid and semiarid regions. On the coarse 

 morainal gravels of the high mountains of Central Europe hemi- 

 cryptophytes and chamaephytes come first (Braun-Blanquet, 1926, p. 

 207). On finer moist gravel cushion mosses such as Pohlia, Poly- 

 trichum, and Rhaconiitnum canescens precede. On the great basaltic 

 blocks of the volcanic peaks of Auvergne and in the upper Rhone 

 region, the carpet moss, Rhacomitrium lanuginosum, first spreads its 

 silvery green tapestry (r/. Fig. 153). On the hard, wet clay of middle 

 European swamps the rhizome geophyte Tussilago farfara plays an 

 important role as pioneer colonizer. The erosion furrows and washouts 

 in the Tertiary marls between the Rhone and the Aude are colonized by 

 hemicryptophytes and shrubs, in spite of the enormously superior seed 

 development of the abundant neighboring therophytes. 



Birger (1906) had the opportunity to observe for many years the 

 devielopment of vegetation on a new island in Hjalmar lake (Sweden) 

 caused by a fall in the water level. Four years after the change of 

 level had occurred, 2 mosses and 113 phanerogams had become estab- 

 hshed. These included 40 individual trees belonging to five different 

 species. Six years later there were 12 lichens, 18 mosses, and 184 

 phanerogams, of which 10 were trees. Twenty-two years after the 



