THE GEOGRAPHY OF FRUIT GROWING 



617 



other names to designate them than the biological cartographer does. 



These general life zones as determined for the United States, southern 



Canada and northern Mexico 



by the Bureau of Biological 



Survey of the United States 



Department of Agriculture, are 



shown in Fig. 65. 



The Boreal Zone. — As here 

 outlined, the Boreal zone or 

 region includes all of Canada 

 except a portion of Nova 

 Scotia, a strip along the St. 

 Lawrence River and running 

 west through Ontario to Lake 

 Huron and Georgian Bay, 

 southern Saskatchewan and 

 limited areas in southern 

 Manitoba, Alberta and British 

 Columbia. Its southern boun- 

 dary dips down into the United 

 States so as to include parts of 

 northern New England, north- 

 ern Michigan, a small strip of 

 northeastern Wisconsin and a 

 considerable part of Minnesota 

 and North Dakota. Irregular- 

 ly shaped areas characterized 

 by the life of the Boreal region 

 are found here and there in 

 New York and Pennsylvania 

 and at some of the higher eleva- 

 tions of the Allegheny Moun- 

 tains as far south as southern 

 Tennessee. In the western 

 parts of the United States 

 there are finger-like projections 

 of this region and isolated areas 

 with its characteristic fauna 

 and flora extending as far south 

 as the state of Zacatecas in 

 Mexico. For the most part these extreme southern extensions are Hmited 

 to the higher elevations of the Rocky, Sierra Nevada, Cascade and Coast 

 mountain ranges. Its southern limit is marked by the isotherm of 18°C. 

 (64.4°F.) for the six hottest consecutive weeks of midsummer. ^^ On the 



