16 BULLETIN, 1105, U. S. DEPARTMENT OF AGRICULTURE. 



In studies at the Fort Valley Experiment Station only the cones 

 produced in 1918 were considered. A group of eight blackjacks 

 ranging from 12 to 16 inches in diameter showed an average yield of 

 135 cones per tree for the 1918 crop. A single blackjack near by, 22 

 inches in diameter, yielded 500 cones. An open group of five black- 

 jacks ranging from 18 to 22 inches in diameter showed an average 

 production of 520 cones per tree. In the last two instances the heavier 

 yield, as compared with the first group, is attributed to the larger 

 size of the trees and better exposure to sunlight. 



A full-crowned yellow pine 27 inches in diameter and about 100 

 feet high, standing in an open space a short distance from the first 

 group of blackjacks mentioned above, yielded 3,500 cones in 1918, 

 equivalent to 10.7 pounds of seed. The mass of half-decayed cones 

 around this tree indicates that its cone production in past years must 

 have been enormous. Within 100 yards of this tree are two yellow 

 pines, 29 and 32 inches in diameter, whose combined yield in 1918 is 

 calculated at 4,200 cones. 



A fact which has been forcibly demonstrated by the cone survey 

 is that it takes large trees to produce quantity of seed. Trees below 

 20 inches in diameter growing in the open often give the impression 

 of being large seed producers, but an actual measure of their crop 

 will show that their yield is but a small fraction of that of a similarly 

 situated large tree. 



The cone survey also indicates that large blackjacks are, as a rule, 

 less productive than yellow pines of the same diameter. This is 

 probably due to the fact that a yellow pine is usually much taller 

 than a blackjack of equal diameter. 



According to the foregoing comparisons, yellow pine has a seed- 

 producing value about six times as great as that of blaclfjack. Con- 

 sidering, however, that yellow pine is a greater risk than blackjack, 

 with reference to windfall, lightning, and general deterioration, a 

 ratio of 5 to 1 is believed to be more reliable. After making due 

 allowance for all factors which have been mentioned, the following 

 have been adopted as conservative figures for yields on Forest Service 

 cuttings in average seed years: Yellow pine, 2^ pounds per tree; 

 blackjack, one-half pound per tree. These figures are admittedly 

 crude and should be replaced as soon as possible by data based on 

 actual yields in cut-over stands, but it is believed that their use is 

 warranted in preference to a mere guess. 



Using the preceding figures as a basis for calculations, the re- 

 quirements for an adequate seed supply are 3 or 4 yellow pines or 

 16 blackjacks over 11 inches diameter breast high per acre. Stands 

 of either pure yellow pine or pure blackjack are, however, rarely 

 encountered. The usual practice on Forest Service lands is to leave 



