26 



BULLETIN" 871, U. S. DEPARTMENT OF AGRICULTURE. 



to determine just what the limits of the intermediate class should he, 

 so in order to preclude any error in judgment the procedure as first 

 stated of establishing just two classes, dominant and suppressed, to 

 include all the trees, is followed throughout. 



The method of obtaining the volume of the tree in cubic feet 

 requires a little explanation. Each tree was considered as a perfect 

 cone over the stump, at which the age count had been taken, in 

 order to obtain directly comparable figures for the different ages. 

 Figures from normal trees showing the relation of the diameter 

 breast high to diameter of butt at stump height (1.5 feet) were plotted 

 and curved, the strongest portion of this curve lying between 10 and 

 50 inches diameter breast high. From this curve a table expressing 



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Fig. 1.— Comparison of average volumes of incense cedar on the optimum and intermediate areas. 



the relation of tho diameter breast high to diameter of butt at stump 

 height for each inch class was read. It was then a simple matter to 

 secure the diameter outside the bark at stump height for any tree, no 

 matter how irregular the stump might be, due to wounds or other 

 factors, and combining this with the height to work out the total cubic 

 contents. Loss of volume caused by wounds or other factors was dis- 

 regarded. In other words, each tree was treated as if it was absolutely 

 normal. Let it be emphasized again that the volumes obtained were 

 not meant to be an exact expression of the actual volume of each 

 tree to the last cubic foot but merely had to be directly comparable 

 to each other for the various ages. 



In considering the trees with decay, each separate iocus of dry-rot 

 is termed an infection, and there may be two or more infections in 





