8 



Prolonging the Cut of Southern Pine 



years is for average trees, and shows that timber reaches mer- 

 chantable dimensions from seed in from forty to fifty years. This 

 is borne out by the growth of old-field stands. Six plots of five 

 acres each measured in old-field stands showed yields of from 

 7,500 feet b.m. to 14,200 feet b.m. per acre, with ages from 

 forty to forty-seven years. The more rapidly growing trees reach 

 merchantable size in thirty years and old-field stands will yield 

 2,000 to 3,000 feet b.m. per acre when thirty-five years of age. 

 In the next few years the yield of merchantable timber rapidly 

 increases as the trees attain merchantable size. 



Table 2. — Average Yield per Acre of Even-Aged Stands of Shortleaf 

 Pine, Under Ordinary Conditions, on Large Areas 

 in Ashley County, Arkansas. 



(Doyle Rule) 



Dense stands with a large number of trees per acre, such as 

 occur on old fields, cannot maintain both numbers and rapid 

 growth. The increasing demands of larger trees for soil moisture 

 during the growing season cause the number of trees which can 

 continue to thrive on an acre to diminish rapidly. When most 

 of the trees are of nearly the same age and height, the crowding 

 out of the weaker trees does not take place as rapidly as it should, 

 and the growth of all the trees may be seriously retarded. In the 

 ordinary forest the same crowding and loss of numbers occur, but 

 the more broken and irregular character of the stand makes it less 

 pronounced. Under average conditions yields of timber can be 

 depended on to equal or exceed the results given in Table 2. 



In fact, better yields per acre than this are obtained in the 

 virgin forest on many "forties," and with any sort of management 

 which secures good reproduction and affords protection, these 

 yields should be increased by one-half, as is shown by the yields 



