[Chap. LIU THE VEGETATION OF NORTH AMERICA 



751 



the white spruce forest is regarded as the chmax community or associa- 

 tion of the boreal forest formation. 



Hemlock-hardwood forest (Figs. 378-380). From Winnipeg through 

 the Great Lakes region to Nova Scotia, and at gradually increasing eleva- 

 tions southward in the Appalachians, is a far more complex formation 



Fig. 380. Interior view of a mixed spruce-hemlock -hardwood forest in the Mononga- 

 hela National Forest of West Virginia. Photo from U. S. Forest Service. 



composed of many more species of plants and consequently of a greater 

 number of distinct communities. 



This plant formation was originally characterized by the abundance 

 of hemlock, eastern white pine, red pine, yellow birch, red spruce, sugar 

 maple, red maple, beech, and black cherrv. The hemlock-hardwood for- 

 mation extends between the boreal forest formation and the deciduous 

 forest formation on the south. Since general climatic regions are never 

 separated by sharp lines because topograph)^ modifies climatic factors 

 locally, many small areas containing boreal communities ha^'e persisted 



