not hypothetical inferences about the relations between vegeta- 

 tion and the environment. ^^ 



Successional Status 



Classification of units on the basis of succession (syndynamics) 

 has been widely used in the United States and in other countries 

 where emphasis on plant physiology and plant processes is 

 strong, and also where natural vegetation occurs following the 

 destruction of the original plant cover or where it was greatly 

 disturbed by man or animals. The most exhaustive classification 

 based on this criterion, vegetation dynamics, is by Clements in 

 his book "Plant Succession."'*^ An example illustrating the use 

 of stages in secondary succession in classifying the vegetation 

 types is taken from a study on abandoned crop land in the Pike's 

 Peak region in Colorado (Figure 6-3).*^^ 



(1) Initial stage: annual forbs and grasses 



(2) Perennial forb stage: perennial weedy forbs, grasses, and 

 a few shrubs, persists for 3 to 5 years after cessation of culti- 

 vation 



(3) Mixed grass and weed stage 



(a) Stipa-Agropyron phase, duration about 10 years 

 {b) Stipa-Bouteloua phase, develops within 15 to 25 years 

 after abandonment 



(4) Subclimax bunchgrass stage: Muhlenbergia montana and 

 Festuca arizonica as dominants 



(5) Climax: Pinus ponderosa and Pseudotsuga taxifolia as 

 dominants 



In each of these stages several kinds of communities may be pres- 

 ent; for example, in the first stage nearly pure stands of Setaria 

 viridis, Chenopodium album, and Helianthus annuus are found, as 

 well as mixtures of these and other species. It is important to 

 analyze and describe the communities in each stage, but too often 

 this has not been done. Such analysis would undoubtedly reveal 

 many community-soil relationships and differences in the course 

 of succession in relation to site conditions. 



The successional approach has limited usefulness in areas 



184 • Classic icatiozm of ConmBiamaBmities 



