312 THE STUDY OF PLANT COMMUNITIES ■ Chapter XI 



plains. Any such condition may be effective in maintaining relict 

 communities, which, in terms of climate, could not be anticipated. 

 They are the relicts indicative of shifts of climax and climate over 

 long periods. 



FlG. 168. Effect of grazing on mixed prairie in central Colorado. Short 

 grass, to left of fence, is typical over much of the region but, where cattle 

 are excluded, to right, mixed prairie develops.— Photo by R. B. Livingston. 



A quite different kind of relict is one that is maintained by man, 

 purposely or otherwise, after he has destroyed or modified the 

 picture of climax generally. Overgrazing, cultivation, and lumber- 

 ing have destroyed or modified climax over extensive areas to such 

 a degree that its recognition and interpretation, even though its 

 destruction was within historic time, are dependent upon rem- 



