PLANT SUCCESSION 229 



region. In or approaching transition zones, such areas are partic- 

 ularly noticeable, and here, especially, application of the concept 

 greatly simplifies interpretation of climax. 



Since communities such as these exist to some extent in every 

 climatic area, they must be recognized. As mentioned earlier, not 

 all ecologists agree as to their interpretation. Some, with the poly- 

 climax view, describe them variously as edaphic or physiographic 

 climaxes. This is open to the general criticism that, by definition, 

 there can be but one climax for a climatic region. Use of preclimax 

 and postclimax is a necessary part of the monoclimax view but is 

 consistent with the meaning of climax. At the same time, it shows 

 relationshiDS with contiguous and past climaxes. 



METHODS OF STUDYING COMMUNITY DYNAMICS 



Determination of Climax Formations.— The major climax re- 

 gions (formations) are fairly obvious, and their number and ap- 

 promixate limits have been accepted for some time. Each has its 

 distinctive physiognomy or life form that makes for clear demar- 

 cation. An additional number of criteria corroborating the appar- 

 ent unity based upon physiognomy have been applied. 



Tests of climax that have been used in fixing formations 00 are 

 briefly summarized below. Both static and developmental criteria 

 must be met. 



Static Criteria 



1. Life form must be uniform throughout. 



2. All associations must include one or more of the same 

 or closely related species as dominants or subdominants. 



Developmental Criteria 



3. Late stages of succession must be essentially identical 

 for a climax; and distinct from those of another climax. 



4. Postclimax should show relationships to contiguous cli- 

 max or subclimax. 



5. Historical records as to composition and structure must 

 conform to the modern picture. 



a. Recent historical— old records and land surveys. 



b. Historical development reconstructed from pollen 

 statistics. 



c. Geological record, physical history, and fossils. 



