42 



BULLETIN" 308, U. S. DEPARTMENT OF AGRICULTURE. 



The yield in saw timber of a crowded stand 30 years old is very 

 small, because very few trees have attained a merchantable diameter. 

 The largest diameters occur in understocked stands, which yield con- 

 siderably less, however, than fully stocked thinned stands. If the 

 material derived from the thinnings is of sufficient value to pay for 

 the cutting or to yield a profit, the cost per thousand feet of growing 

 saw timber in fully stocked thinned stands is less than in either 

 crowded or understocked stands. If thinnings do not pay for them- 

 selves the cost is greater. At the age of about 48 years, when thinned 

 stands reach their maximum annual yield, the diameter of the average- 

 sized tree is about 9.5 inches breast high, or 11.5 inches on the stump. 

 The average annual yield of saw timber at that time from trees 9 

 inches and over in diameter is 410 board feet. For similar unthinned 

 stands the maximum annual yield occurs at the age of about 57 years, 

 and the tree averages 8.2 inches at breast height, or 9.8 inches on the 

 stump. The annual increment at different ages from unthinned and 

 thinned stands is shown in Table 21. 



Table 21. — Average annual increment per acre of saw Umber from thinned and 

 unthinned shortleaf -pine stands in Virginia. 



[Trees 9 inches and over in diameter, measured at breast height.] 



Age. 



Thinned stand (thin- 

 nings neglected). 



Unthinned stand. 



Average 



annual 



increment. 



Periodic 

 annual 

 increment 

 for each 

 decade. 



Average 



annual 



increment. 



Periodic 

 annual 

 increment 

 for each 

 decade. 



Years. 

 30 

 40 

 50 

 60 

 70 



Bd. ft. 

 280 

 410 

 408 

 383 

 357 



Bd.ft. 



Bd.ft. 



Bd.ft. 



800 

 400 

 260 

 200 



150 

 262 

 250 

 238 





710 

 190 

 170 



In calculating the cost of growing shortleaf pine saw timber, com- 

 pound interest on the value of the land, accumulated taxes, and other 

 expenses must be considered. The effect of thinning upon the final 

 yield and upon the cost of growing shortleaf pine are shown in 

 Table 22. The calculation assumes a land value of $5 per acre, 

 taxes and other expenses at the rate of 1 per cent on the land value, 

 and net annual returns of 5 per cent on the investment in land and 

 cost of stocking. The lowest cost for unthinned stands was $6.25 and 

 for thinned stands $2.21 per thousand feet. The age at which the 

 cost is lowest, or the financial maturity of the timber, was 45 years 

 for natural stands and 35 years for the thinned stands. 



