12 



COMPOSITE TYPE OK THE APACHE NATIONAL FOEEST. 



A glance at figure 1 or a study of Table 3 shows the growth of 

 spruce after the period of early youth is passed to be the greatest of 

 the three. In the case of spruce, however, the maximum is reached 

 at an earlier period in the life of the tree and the growth falls off 

 sooner than in the case of the two other species. The diameter growth 

 of western yellow pine and Douglas fir is practically the same until 



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Fig. 1.— Growth in diameter in relation to age of western yellow pine, Douglas fir, and blue spruce. 



the age of 100 years is reached, when Douglas fir gradually forges 

 ahead. The curves show at what ages the rate of growth of the 

 three species begins to decline. Blue spruce noticeably falls off in 

 diameter growth at 100 years of age. The growth of yellow pine is 

 well sustained until it is 180 years old, and that of Douglas fir for 

 40 years longer. 



