Investigating Yield Per Acre. 463 



correct the mapped areas by eliminating a proper amount of 

 space from the veteran area for younger trees, and adding it 

 to the classes below. To find how much space to eliminate, di- 

 vide the total known area mapped as "mature" trees by the num- 

 ber of "mature" trees occupying it, and the result gives the space 

 taken by an average mature tree. This space multiplied by num- 

 ber of mature trees on the veteran areas indicates the correction 

 in area. There is no doubt that this correction enables one to 

 greatly simplify the field work of mapping, which is the funda- 

 mental point in the whole plan. Its application is merely a mat- 

 ter of a little computing. 



The second essential is now secured, the area occupied by each 

 age class. To get the third, the age, two plans are possible. The 

 first is to determine the volume of the average tree for an age 

 class, get its diameter, and fell one or more trees of this diameter 

 to determine the age. This age is taken to be the age of the class. 

 This plan should be used whenever there is no logging 

 operation going on in timber growing in the vicinity on the same 

 type and quality of soil. Its drawback is the danger that the tree 

 or trees cut will show faster or slower growth than the average 

 for the stand. 



The second plan is to determine the diameter of the average 

 tree, but instead of felling trees to get the age, this is taken from 

 a curve of growth in diameter based on age, prepared from 100 to 

 200 stumps measured in the vicinity, and corrected to D. B. H. 

 and for the age of the seedling. If the timber is of the same type 

 throughout, this plan is best, as it produces tolerably surely 

 average growth figures and gives average age. 



In either case, the method of finding the diameter of the average 

 tree can be the same. Averaging diameters directly is admittedly 

 a wrong method. Determining the average basal area and from 

 it determining the diameter is theoretically sound, but this method 

 is used only to determine cubic contents. For board feet, this 

 determination should be made with the aid of a volume table 

 based on diameter and height. To get the volume of the stand 

 originally, the volumes of all trees in the stand have been com- 

 puted from such a table by first preparing the curve of average 

 height to diameter. Volumes from this volume table can now 

 be written in on this height curve, since Vv^ith height determined. 



