16 COMPOSITE TYPE OX THE APACHE NATIONAL FOEEST. 



addition to this it is often swell-butted. The pine has medium thick 

 bark, but comparatively little taper, and the bole, especially at old 

 age. fills out well. 



The difference in volume is even more pronounced than the differ- 

 ence in merchantable length. Spruce, on account of its great taper, 

 produces no merchantable log until it reaches a diameter of 14 

 inches. At this diameter western yellow pine has a merchantable 



Fig. 3.— Growth in volume of western yellow pine, Douglas fir, and blue spruce. 



length twice as great, and Douglas fir nearly as much. A better 

 comparison of the volumes can be obtained if age is taken as a basis. 

 Table 6 gives the volume of each species in both board and cubic 

 measure at 10-year intervals. On account of the inaccuracies in 

 the decimal "C" rule, or in fact, in any board foot measure, a more 

 exact comparison of the three species may be made from the columns 

 headed '•Volume, cubic feet." 



