PAPERS OX BOTANY 243 



TOPOItEAPHIC EELIEF as a FACTOE IX PLAXT 



SUCCESSIOX 



Geo. D. Fuller, Uxh-eesity of Chicago 



It is uow generally accepted that there is a tendency 

 for one plant community to pass to another in a some- 

 what definite series, from the pioneer vegetation of a 

 region through successive phases to a community that 

 is very decidedly richer and more mesoph^i:ic than any 

 of the earlier vegetation. This series of changes has 

 been designated plant succession, and has been exten- 

 sively discussed by Cowles (1), Clements (2), and oth- 

 ers. The final phase in the succession differs from the 

 pioneer and intermediate ones, not only in its greater 

 mesophytism, but also in its permanence and is termed 

 the climax phase. Throughout the northeastern United 

 States the climax plant community is a mesophytic for- 

 est in which deciduous trees predominate, and it has been 

 assumed by many that all parts of the region will event- 

 ually be dominated by this, the richest type of vegetation 

 that the climate is able to support. Progress towards 

 this climax will vary much in the character of the differ- 

 ent stages and in the rapidity with which they succeed 

 one another, the differences being determined largely 

 by the character of the soil, the development of its drain- 

 age, and the composition of adjacent vegetation. Man's 

 activities in cutting and burning may cause temporary 

 or even permanent halting or retrogi'ession, but other- 

 wise the progress will be steadily towards the climax 

 even although the movement be imperceptibly slow. 



While many ecologists have regarded the climax vege- 

 tation as limited by the climate only, others have 

 seen in soil a limiting factor and recognized the establish- 

 ment of permanent plant communities of distinct char- 

 acter due to the conditions of the soil. These communi- 

 ties would be called "edaphic climax communities," and 

 they would be less mesophytic than the climatic climax of 

 the region. Such communities have also been termed 

 ''temporary climax communities" by those who believe 

 that they will eventually pass to the climatic climax, al- 



