72 A MILL SCALE STUDY OP WESTERN YELLOW PINE. 



Growth. 



The growth determinations shown in the following diagrams are based 

 on measurements of the average radii of stamps of felled trees of known 

 dimensions. The average rate of growth of each individual tree, as 

 shown by the last fifty annual rings formed, or last fifty years of the life 

 of each tree, was determined. These rates were then corrected so as to 

 read at diameter breasthigh by means of reducing factors, as shown in 

 Figs. 81 and 82. Trees were then grouped in diameter classes, and 

 those of each diameter class were arranged according to rate of growth, 

 from the minimum to the maximum. The number of trees forming 

 each class is the sample of that class, and an individual tree therefore 

 may represent a large percentage of the sample or a small one, .-ill 

 depending upon the total number of trees included in the class. 



The larger the number of trees composing a sample the more authentic 

 are the final results, since the variability from the true minimum to the 

 true maximum can thus be more closely obtained. In any sample on 

 rate of growth it would be absurd to assume that the minimum indi- 

 cated applied to the slowest growing tree in the timber region being 

 studied, or that the maximum of the sample was the fastest growing 

 tree. After determinations on about seventy-five or one hundred trees 

 have been made for a diameter class, the value of the sample is increased 

 very slowly by the addition of more trees; since the principal effect of 

 additional trees will be to lower the minimum and raise the maximum, 

 while the body of the sample will be practically unaffected. 



In Figs. 83 and 84 samples for the various diameter classes are com- 

 pared. These samples are not composed of the same number of trees ; 

 had they been, the final results would have been very little different 

 from these here given. In fact, the number of trees comprising each 

 diameter class shown in Figs. 83 and 84 is a better sample than though 

 the number in each case were the same, since these numbers are to a 

 large degree representative of the quantity of trees of each diameter 

 class to be expected from a given tract similar to the one under con- 

 sideration. 



Curves shown in Figs. 85 and 86 are plotted directly from Figs. 83 

 and 84, and show the rate of growth per decade at diameter breastl'igh 

 of trees of different sizes. Curves 87 and 89 were obtained by plotting 

 the increments of total sawed out volume in board feet as indicated by 

 the diameter growth. Figs. 88 and 90 were obtained by expressing 

 curves in Figs. 87 and 89 in per cent of total sawed out. 



Curves shown in Figs. 91 and 93 were obtained by plotting incre- 

 ments of total value per tree, as indicated by the diameter growth for 

 the average, and then for the highest and lowest ten per cent, while 

 Figs. 92 and 94 show the same results expressed as a per cent of the 

 total value per tree. 



The, relation of growth to grades or quality . 



Wood formed by the growth of western yellow pine trees after they 

 have reached maturity is very fine grained, free from knots in the lower 

 part and uniform in texture. No new limbs are formed after maturity. 

 as evidenced by the absence of small live branches. All living branches 

 are large, and usually high up in the tree. Therefore, no new knots 



