Investigating Yield Per Acre. 465 



classes, too large an area given to one class is sure to mean that 

 too much is taken from one or more of the other classes. The 

 abnormality is indicated almost without exception as soon as the 

 results are worked up. A second trip to the field, and a new map 

 fo the same plot, with the previous error in mind will result in a 

 much closer approximation of the facts and will go far towards 

 giving the needed experience. 



Differences in the work of two crews, which are caused by dif- 

 ferent standards or limits for age classes are immaterial. If one 

 crew includes twice as many trees in the veteran class as another, 

 their average volume will be smaller, as smaller trees will be taken. 

 This gives a lower age. and a different yield per acre. The area 

 mapped will naturally be larger, to include the extra trees. The 

 result is simply that a different point in the yield table is obtained. 



This method seems to open up many possibilities in the study 

 of growth, provided investigators will not allow themselves to be 

 frightened off by its apparent flaws. Owing to the importance of 

 the results attained, one illustration is appended, of a twenty-acre 

 lot studied by three crews. The difference in results obtained 

 may serve to illustrate the elasticity of the method and bring out 

 its good and weak points. 



Age; Class Distribution. 



Crew No. 3 put only the largest timber into the veteran class. 

 Crew No. 2 included probably too great a proportion of the stand 

 in the young class. 



Areas Mapped in Field, as Finally Corrected, in Acres. 

 Crew. Veterans. Mature and Young. Immature. 



1 2.26 13.28 4.46 



2 373 7-8i 8.45 



3 3-33 9-67 7-00 



