PREDICTION OF GROWTH 



323 



this case, instead of predicting exact future growth, is used as a standard 

 to express the relative increase or decrease in the yield or stand per acre. 

 The yields may be plotted and will form curves of growth in volume, 

 per acre. The yield of any stand whose present volume and age are 

 known represents a definite per cent of some existing yield from this 

 table. The growth of this stand may be predicted by using the same 

 per cent of the values in the table for the future. 



In Fig. 66 the present yield of a plot of white pine of fifty years is 

 indicated and the basis of prediction for its future yield is shown. 

 This percentage relation based upon standard yield tables is exten- 

 sively applied in forestry to obtain the actual yields of large forest 



10,000 



9,000 



« 8,000 



^7,000 



•g0,OOO 



55,000 

 ■g 



fl 4,000 



13,000 



> 2,000 



1,000 







25 30 35 40 



45 50 55 

 Age in Years 



Fig. 66. — Method of predicting yields of specific stands by comparison with standard 

 curves of yield for different qualities of site. White Pine, Mass. 



areas. It is the basic idea underlying the prediction of growth by 

 the method of comparison. 



251. Prediction of Growth by Projecting the Past Growth of Trees 

 into the Futiire. By either of these methods, comparison or projec- 

 tion, it is assumed that no records exist of the past condition of the 

 stands whose growth is to be found. Their present volume, and the 

 age and past growth in diameter, height and volume oj the trees now 

 standing can be studied, but there is no reliable indication of the 

 number of trees lost during the past period, though evidences remain 

 for a time in the form of dead and down trees. ^ 



^ The writer once noticed in a densely stocked stand, the stems of hundreds of 

 small lodgepole pine which had fallen across a tamarack log and been preserved from 

 decay, when all trace of similar dead trees on the forest floor had disappeared. 



