ECOLOGY AND WILD LIFE CONSERVATION 



475 



Biomes 



Since the types of vegetation control to a large extent the distribution 

 of many species of animal life, we must classify the ecological habitats 

 in terms of dominant plant associations, called biomes. Of course, ani- 

 mals do affect these plant formations in many ways. Caterpillars may de- 

 stroy or at least severely damage many trees in an area and make room 

 for smaller shrubs. The American buffalo is believed to have extended 

 the grasslands biome by destroying the woody plants along its bound- 

 aries. Deer and elk will browse so severely on the bark of aspens and 



Photo by Winchester 



Fig. 30.1. A beaver dam and the lake formed by it in the Rocky Mountain region of 

 Colorado. These dams are of great ecological significance. 



other trees during long cold winters that the trees will die and so open 

 up the woods. Beaver will dam streams and form lakes in which sedi- 

 ments will accumulate year after year. In New York State hundreds of 

 feet of such sediments have accumulated in some of the valleys creating 

 a rich soil. Beavers also cut down the trees around their dams and 

 form an opening in the forest which will bring in new species of birds 

 and other animals. Birds also plant many species of plants by carry- 

 ing the seeds in their digestive system and dropping them from some 

 favorite perch. When a tree dies in the middle of a pasture birds will 

 sing from its dead branches and there springs up beneath their perches 

 blackberries, green briers, sassafras, dogwood, persimmon, red cedars, 

 and other species producing highly colored, edible berries. 



