Method for Regulating Yield. 25 



qualities of locality sites, time will be saved at slight expense in 

 accuracy. Then divide the square feet in an acre, 43,560, by the 

 number of diameter classes. The quotient will give the total 

 area which normally should be occupied by each diameter class. 

 But this is only a preliminary step, because the real information 

 desired is the answer to the question, "How many trees should 

 there normally be in each diameter class?" The answer is easily 

 found in each case by dividing the total area occupied by the 

 diameter class, by the average crown-spread of the average tree 

 in that class. 



For a forest type and quality of locality capable of forming an 

 unbroken crown-canopy the above operations will give the actual 

 number of trees which would be normal in each diameter class ; 

 but for other conditions these numbers will express only the 

 normal proportion in the trees of the different diameter classes. 

 This, alone, should be of considerable value in measuring the 

 abnormality of the stand in respect to normal diameter distri- 

 bution; yet the deductions are still in a clumsy form for practical 

 use, and the following improvement, although introducing a 

 source of inaccuracy, is suggested : 



Determine for the different types on the different sites the 

 total crozvn-spread per acre in the best stocked stands you can 

 find, considering only the trees that are unsuppressed, or only the 

 dominant and co-dominant trees. Assume that such stands are 

 normal in respect to crown density. Express by a fraction the 

 relation existing between the actual total crown-spread in square 

 feet and 43,560 square feet. With the reducing factor thus 

 found multiply each number representing the normal proportion, 

 and the normal number of trees in each diameter class zmll be 

 found. 



The foregoing explanations are made concrete in the following 

 imaginary example in which the reducing factor is .8, the other 

 data as given, and the diameter limit is 16". 



