LIFE FORMS AND SYNECOLOGICAL UNITS 



301 



biological spectrum of the primitive beech wood of the south Cevennes 

 (Table 35) Fagus plays only a most insignificant role (2 per cent), 

 although it is pronouncedly dominant over all other species ; in fact, it 

 directly determines the entire association, which is strikingly character- 

 ized by the large number of geophytes. The loose, fertile upper-soil 

 horizon favors the development of the rhizome geophytes, while 



Fig. 152.- 



-Fruticose lichen association on a tree stump in fir woods {Cladonia alpestris, 

 C. silvatica, Cctraria islandica). {Photo by Heller.) 



considerable shading hinders the growth of therophytes. The sig- 

 nificance of the phanerophytes appears in its proper light only 

 when, along with life forms, the structural details of the com- 

 munity, such as number, mass, and layering, are duly considered (see 

 Chap. III). 



Synecological Units. — The general physiognomy of communities, 

 based upon life forms, leads to the recognition of more or less uni- 



