582 



INTERRELATIONSHIPS OF ORGANISMS 



of local geological processes. We know that the present climate of the 

 region about the southern half of Lake Michigan is geologically very 

 recent, perhaps too recent to have permitted the slower successional 

 sequences to have developed to a climax community. Moreover, local 

 geological processes are continuously providing new situations for pioneer 

 communities or are retarding or setting back the potential successional 

 sequence. 



Fig. 33.17. Mountain meadows and coniferous forests on Mount Rainier, Wash., at about 

 5,000 feet altitude. In early summer this is a veritable subalpine flower garden, with 

 heathers, daisies, anemones, columbines, larkspurs, pasqueflowers, lupines and many other 

 flowers blooming in profusion. The summer season is short, and only plants which can 

 mature their seeds rapidly and endure long, cold winters can survive. This environment is 

 much the same and has many of the same species as the arctic meadows that lie near sea 

 level in Alaska. It is the home of marmots, pikas, bighorn sheep, and Rocky Mountain goats. 

 (Courtesy Carnegie Museum, Pittsburgh.) 



New sand dunes, for instance, continue to form along the southern 

 and southeastern shores of the lake and as they gradually move inland, 

 until stabilized by the sand-dune pioneers, destroy areas of late-stage 

 succession on parts of the earlier dunes and produce new ponds and 

 marshes by damming the former drainage. Elsewhere, stream erosion 

 is producing new sand bars and mud flats or exposing new clay banks or 

 rocky cliffs. The dwindling lakes of a former geological period still present 

 shore lines and shallow basins for occupancy by the pioneer communities 



