CLIMAX COMMUNITIES : PRESENT DISTRIBUTION 237 



These, together with their associations, are discussed in the section 

 that follows. The formations restricted to the mountains of the 

 west occur in altitudinal zones whose relationships should be clear- 

 ly understood. Consequently, discussion of these zonal formations 

 is centered about each of the principal mountain ranges rather 

 than considering each zone separately, throughout its extent. 



Climax Formations of North America 

 Tundra 



Tundra Formation 



Forest 



Coniferous 



Boreal Forest Formation 



Subalpine Forest Formation 



Montane Forest Formation 



Pacific Coastal Forest Formation 

 Deciduous 



Deciduous Forest Formation 

 Woodland 



Woodland Formation 

 Scrub 



Broad-Sclerophyll Formation 



Sagebrush Formation 



Desert Scrub Formation 

 . Grassland 



Grassland Formation 

 Tropical Formations 



Tundra Formation.-Tundra lies between the northern limit of 

 trees and the area of perpetual ice and snow in the far north, or 

 above timber line in high mountains. In North America, it forms 

 a broad band completely across the continent, and it also occupies 

 the narrow low coastal area around most of the periphery of 

 Greenland. It occurs on mountains as far south as Mexico if their 

 altitude is sufficient to produce a timber line. Thus it is limited in 

 its northern or upward extent by ice and bounded on the southern 

 or lower margin by boreal or subalpine conifer forest. 



Vegetation is low, dwarfed, and often matlike, and includes a 



