322 



PRINCIPLES UNDERLYING THE STUDY OF GROWTH 



From the above table, the periodic growth for separate five-year 

 periods may easily be obtained by subtracting the volume at one age 

 from that of the succeeding period. 



250. The Application of Yield Tables in Predicting Yields. An 

 example of the prediction of volume growth in existing stands of timber, 

 on the basis of periodic growth by decades is given in the following 

 table which shows the present yield of timber over 10 inches and the 

 future yield which may be realized upon the timber left standing below 

 this diameter limit, and not shown in the table. 



TABLE XLIX 



Yield pek Acre of Spruce Ctjtting to Various Diameter Limits * 



Based on stands containing approximately 5000 feet B.M. of timber 10 inches 

 and over in D.B.H. per acre 



* Compiled from Yield Tables in " Practical Forestry in the Adirondack^,' 

 of Forestry, U. S. Dept. Agr., 1899, pp. 83 and 84. 



Bui. 26, Division 



To understand the use or application of a yield table in predicting 

 growth, it must be realized that the stand or rate of growth upon a 

 given acre or tract will seldom if ever exactly agree with that shown in 

 a yield table even when these yields are separated by qualities into 

 3, 4 or 5 classes of site. In the case of bare land or very young timber, 

 this probable difference may be ignored, the site regarded as equivalent 

 to one of the site classes given and the yield predicted as if it would 

 coincide with that of the table. But for most stands which have already 

 reached a considerable age and the prediction of whose further growth 

 is desired, a comparison with the yield table should give a more exact 

 prediction of the growth of the stand in question. The yield table in 



