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GEORGE E. NICHOLS Vol. IV, No. 2 



E. Types of Succession in Relation to Climax 



The nature of the climax which is capable of attainment in any area is 

 controlled in large measure by geographic conditions — by climate, on the one 

 hand ; by physiography, on the other. This is true, regardless of the factors 

 by which the succession is instituted. Generally speaking, geographic condi- 

 tions tend to act as limiting factors to prevent development from progressing 

 beyond a certain stage (or vice versa). In a desert region, for example, the 

 attainment of a mesophytic forest climax is prevented by unfavorable climatic 

 conditions ; in saline situations along the seacoast it is prevented by unfavor- 

 able physiographic conditions. In relation to the geographic conditions of 

 any particular region two types of climax may be distinguished, namely, 

 climatic and physiographic. 



A climatic (or regional) climax is one determined by climate. It is an 

 association of the most advanced type that is capable -of development under 

 the climatic conditions which characterize a climatic region. Practically 

 speaking, it is a climax of the type which tends to develop on the better soils 

 throughout the region, on well-drained and approximately level or rolling 

 areas, in places where the vegetation is not exposed to the influence of localized 

 climatic or physiographic agencies — i.e., on "ordinary uplands." Through- 

 out most of the eastern United States, for example, mesophytic deciduous 

 forest represents the climatic climax type. 



A physiographic climax 59, is one determined by physiography. It is an 

 association of the most advanced type that is capable of development in any 

 physiographically uniform area. In a rock ravine, for example, the moist 

 banks, the dry cliffs, and the wet ledges would each be characterized by a 

 different climax because of their physiographic dissimilarity. 



The distinction here made between climatic and physiographic climaces is 

 admittedly somewhat arbitrary, but the underlying idea is one of great practi- 

 cal as well as theoretical importance. It is of course obvious that, strictly 

 speaking (and neglecting for the moment the influence of biotic agencies), the 

 nature of the climax in every habitat is determined by the combined influence 

 of both climatic and physiographic conditions. In any region of essential 

 climatic uniformity, however, the effect of climate as a cause for local vari- 

 ations in the nature of the climax can be practically disregarded, for the 

 reason that climate exercises essentially the same influence everywhere. Prac- 

 tically speaking, then, within such a region it is the physiographic conditions 

 which determine differences in climax, and in this sense the terminal member 

 of every developmental series may be regarded as a physiographic climax. 

 When, on the other hand, it comes to the comparison of climaces in regions 

 which are climatically different, it would seem that both climatic and phvsi- 

 ographic factors must be taken into consideration; and so they must. The 



5S In my 1917 paper I have used the term edaphic climax in essentially this same 



