AGE AS AFFECTED BY SUPPRESSION. ECONOMIC AGE 341 



263. Age as Affected by Suppression. Economic Age. When stands 

 are comparatively even-aged and the trees composing them have grown 

 up as dominant individuals, free from suppression, the actual age of 

 such trees is a fair indication of the age which an even-aged stand would 

 require to produce an equal volume. But under this same definition, 

 the age of a tree which has been suppressed in the early period of its 

 life does not indicate the required age but one considerably greater. 

 The correction of the actual ages of suppressed trees to determine the 

 age desired is known as the determination of economic age. What is 

 wanted is the rate of growth of an average dominant tree on the same 

 site as that occupied by the suppressed trees. Where reproduction 

 takes place under a stand either of the same or of a different species, 

 the problem of growth is one of having two crops of timber on the same 

 land at the same time, and the rate of production per acre is the sum 

 of these two successive crops divided by the total period required to 

 produce them both. To isolate the period required for a single crop, 

 we must determine the rate of growth of the crop as if it were in sole 

 possession of the area. 



A composite growth curve may be built up for average trees by 

 measuring the growth on these trees only down to the point at which 

 they were evidently freed from suppression and substituting from this 

 point on the average growth of seedlings and saplings measured on 

 dominant specimens. For instance, if the first 2 inches of an average 

 tree shows suppression, the average rate up to 2 inches must be taken 

 from other dominant, younger trees, and added to the remaining years 

 to get the total economic age of the tree in question. This factor has 

 been neglected in American growth studies, for the reason that with 

 such species but few attempts have been made to determine total 

 age, investigators being content with ascertaining growth for short 

 period based upon the diameter of the trees. 



