586 INTERRELATIONSHIPS OF ORGANISMS 



natural successional sequences. These intrusions do not eliminate suc- 

 cession, but they do profoundly modify it, introduce new stages and 

 new communities, set back or advance the progress of natural stages, 

 and even change the local type of climax toward which the region trends. 

 Not a few of man's modifications have proved unfortunate for his own 

 long-run and even comparatively immediate needs, and it is becoming 

 increasingly clear that a knowledge of the interdependencies of organisms 

 and communities and of their successional relations is highly necessary 

 for any rational and efficient maintenance and long-continued use of the 

 world's natural biotic resources. 



