THE BIOTIC ENVIRONMENT OF ORGANISMS 



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Fig. 33.11. A stage in the extinction of a small glacial lake in Michigan. The lake, which 

 formerly occupied the entire basin, has been almost filled by the accumulation of plant 

 debris and soil washed down the surrounding slopes. At the edge of the open water is a 

 zone of rooted aquatic plants with emergent leaves — a typical pioneer aquatic community. 

 Later successional stages are represented by the dense semifloating mat of sedges, herbage, 

 and low shrubbery outside the zone of aquatics, and by the bog forest of tamarack, poison 

 sumac, and other woody plants seen in the background. Eventually the entire lake basin will 

 be covered by such a forest. This, in turn, will be replaced by other types of forest spreading 

 in from the margins of the swamp, until in theory the area should eventually attain the 

 beech-maple climax stage. (Photo taken on the E. S. George Reserve, Livingston County, Mich., 

 by J. Speed Rogers.) 



Fig. 33.12. A "wet prairie" in northern Florida, densely occupied by pioneer communities 

 of floating and of rooted emergent plants. In the background can be seen a live-oak ham- 

 mock community. (Photo taken near Gainesville, Fla., by J. Speed Rogers.) 



