14 COMPOSITE TYPE OX THE APACHE NATIONAL FOREST. 



Douglas fir, and almost 30 feet taller than western yellow pine. The 

 greatest difference in height between yellow pine and Douglas fir 

 occurs at 240 years, when the latter species is 6 feet taller. 



Fig. 2.— Relation of height growth to age of western yellow pine, Douglas fir, and blue spruce. 



VOLUME. 



Table 5, made from curves constructed upon the basis of age, 

 shows the growth in volume of western yellow pine, Douglas fir, and 

 blue spruce. For each diameter class above 12 inches is given the 

 age, the number of years required to grow 1 inch in diameter, the 

 number of 16-foot logs, and the volume in both board and cubic feet. 1 



i While this is not the method in general use for making volume tables, it is thought that the resulting 

 figures are correct. Dr aeter age curves were drawn on the basis of age for each crosscut and all the curves 

 of the tree entered on the same cross-section paper. The stump curve has its zero point at the intersection 

 of the vertical and horizontal axes of the rectangular coordinates. The curve for the second crossc-t has 

 its zero on the horizontal axis to the right at the age required by the trees to grow from the ground to this 

 crosscut. (This is determined from a preliminary age height curve.) The curve for the third crosscut is 

 still further to the right at the age required to grow from the ground to this crosscut. The other curves 

 are entered on the sheet in like manner. 



From the resulting diagram the dimensions of different cross sections at various breast-high diameters or 

 ages may readily be determined. 



