TREE GROWTH AXD CLIMATE IN THE UNITED STATES 531 



It is evident from this table that the most vakiable types for forest 

 production purposes are Douglas fir, white pine, and the southern 

 bottom lands. These three stand in a class by themselves. The next 

 group, which includes the southern hardwood coves, silver pine, and 

 sequoia types, are at least 15 per cent less productive. Northern spruce, 

 northern hardwoods, southern pine, and Engelmann spruce come next, 

 with yields 40 per cent less in volume per acre than the leaders. 



The remaining types are so low in productive value that it is seldom 

 that forestry can be practiced on them for timber production alone. Of 

 course, w^here there are protective or esthetic values concerned the 

 forest fully justifies itself. 



