224 THE STUDY OF PLANT COMMUNITIES • Chapter IX 



other in their mature or late stages. Eventually, all successsional 

 trends lead to a single community, which is composed of the most 

 mesophytic vegetation that the climate can support and whose mois- 

 ture relations are average, or intermediate, for the region as a 

 whole. This community, determined by the climate, terminates 

 succession and is called the climax community or climax for that 

 climatic area. It is capable of reproducing itself, and, since it rep- 

 resents the last stage of succession, it cannot be replaced by other 

 communities so long as the climate remains the same. It is, there- 

 fore, a stable community in which the individuals that become 

 overmature and die are replaced by their own progeny, leaving 

 the character of the community unchanged. 



Uniformity and Variation of Climax.— Since climax is determined 

 by climate, the distribution and range of a particular climax should 

 be an indication of a region in which effective climatic factors are 

 equivalent. Climax is a product of all the interacting factors of cli- 

 mate and is, therefore, a better expression of the biological effec- 

 tiveness of climate than man can obtain by physical measurements, 

 which he must interpret. This is well illustrated by the similarity 

 of prairie vegetation over an area with an extremely wide range 

 of several factors, particularly of temperature from north to south. 



On this basis, it might be assumed that a climax would be uni- 

 form throughout its extent. This is true only in part. Certain 

 variations are to be expected, which are related to the great extent 

 of climax regions and the history of different parts of these re- 

 gions. The extent of deciduous forest climax results in transitions 

 to both coniferous forest and grassland. These transitions are not 

 abrupt, and the composition of the climax community is affected 

 for some distance. The deciduous forest likewise illustrates how 

 the time element may be involved in variation. Most of its north- 

 ern extent lies on glacial soils and topography and has occupied the 

 area only in relatively recent times. Unglaciated areas to the south 

 supported deciduous forest throughout the period of glaciation 

 and still do today. Thus there are differences in age of vegetation, 

 topography, and soils, all of which contribute to variation in the 

 deciduous climax. 47 



The obvious uniformity of vegetation in a climax region is in 

 the life form of the dominants, which is definitely a product of 



