CURRENT AND MEAN ANNUAL GROWTH 



317 



effect of this increase for the year upon the average increase is spread 

 over all previous years. 



When the current annual growth curve reaches its culmination and 

 begins to decline, the successive average or mean annual growth figures 

 for each year still continue to increase in spite of this fact, since the 

 amount of growth added to the stand during the year although less 

 than formerly is still greater than the average or mean. 



When the current growth for the year finally falls to an amount 

 equal to the average or mean for the entire crop period, the curve of 

 mean annual growth has reached its highest point. During the follow- 



160 



140 



gl20 

 fa 



sioo 



5 ID 15 20 25 30 35 40 45 50 55 60 65 70 

 Age in Yearg 



Fig. 64. — Current and mean annual growth of a normal stand. 

 Jack Pine Minnesota. 



ing and subsequent years the current growth laid on is less than this 

 mean, hence this average or mean begins to drop, but only to the extent 

 that it is pulled down by the effect of this lesser current annual growth 



for single years upon the fraction, ^ ■. Hence as before, 



age m years 



this mean growth curve falls more slowly than the current growth 



curve. Unless these stands are cut, losses in the stand will finally 



exceed the growth, and the current growth curve would then become 



negative. But until the entire stand is destroyed, the curve of mean 



annual growth will still be positive. When properly computed on the 



basis not merely of volume, but of quality and price increment as well, 



the year of culmination of mean annual growth, rather than the current 



growth data, indicates the maturity of a stand and the age at which, 



if cut, it wUl produce the greatest average yields, when the period of 



production is taken into account. 



