SUCCESSION AL SERIES OF COMMUNITIES 



201 



tion the dynamic or developmental phenomena. For this reason it is 

 necessary sooner or later to classify the i)lant conmiunities according:; 

 to their genetic rehitionshii)s. Tiiis is often nuich more difficult 

 than classifying them according to formations because it inyolves 

 determining the relatixe maturity of each connnunity and this fre- 

 quently cannot be done by observation alone. 



The phenomenon that furnishes a basis for a genetic classification 

 of plant communities is plant succession. This process has been 

 briefly outlined in Chapter XVI and will be discussed in more detail 





^ 



Fig. 88. — Ruderal plants on a secondary bare area. The first stage of a xerarch 



secondary sere. 



in Chapters XVIII and XIX. The development of a climax associa- 

 tion from its beginning on a bare area results in an orderly sequence 

 of communities, each member of the series being replaced by a more 

 mature community until the climax is reached. This is brought 

 about through a progressive change in the habitat due largely to the 

 reactions of the vegetation upon the environment. All of the com- 

 munities concerned in the development of a climax from beginning 

 to maturity may be grouped together into a successional series or, 

 as it is sometimes called, a sere. Usually in every region some exam- 

 ples of all of the developmental stages may be found so that by 

 careful study it is possible to group them in their proper genetic 

 relationships. 



Several types of successional series or seres may be recognized on 

 the basis of their origin. A sere always starts on a bare area. A 

 bare area may be either primary or secondary. A primary bare area 



