318 



PRINCIPLES UNDERLYING THE STUDY OF GROWTH 



246. The Character of Growth Per Cent. The growth per cent of 

 a tree or stand cannot be compared with the per cent of interest earned 

 annually on a fixed capital, since this growth is not separable from 

 the wood capital on which it is laid, and thus causes this capital or base 

 volume to increase annually. To maintain the same rate of growth 

 per cent on this increasing volume, the amount of the annual growth 

 must continue to increase at a geometric rate. Although the increase 

 in volume of a stand during the period of most rapid current growth 

 for a time does approach a geometric rate when compared to a given 

 or fixed initial volume, yet even here the effect of the constantly and rapidly 

 increasing volume of accumulated wood capital upon the current annual 

 rate of increase will cause this rate of growth per cent to drop consistently 

 throughout the entire life of a tree or stand. The actual behavior of 

 the growth per cent of a stand is shown by the following table: 



TABLE XLVII 



Growth of Jack Pine, Minnesota * 



♦From Bui. 820, U. S. Dep. Agr., 1920, Table 10, p. 14. 



247. The Law of Diminishing Numbers as Affecting the Growth 

 of Trees and Stands. The growth in volume of individual trees tends 

 at first to follow a rate of geometric increase. Were the diameter growth 

 of trees to remain uniform for a long period, a condition characteristic 

 of many species, notably white and sugar pine, the resultant area and 

 volume growth would increase at a ratio similar to that of D^, rather 

 than D (§ 270). This rate of volume growth is strengthened by height 

 growth. With maturity, the height growth of trees falls to insignificant 

 proportions and the diameter growth of many species falls off to a marked 

 extent. The result is a flattening out of the curve of volume growth, 



