REPRODUCTION OF WESTERN YELLOW PINE. 13 



Yellow pines bear more seed than blackjacks, because of their 

 greater size and because their greater height gives them better ex- 

 posure to sunlight. (PI. I.) Individual trees in the blackjack class 

 may produce as much as yellow pine, but the average yield for black- 

 jack is brought down by the great number of nonproductive small 

 trees. In the yellow-pine class yield rises steadily with diameter up 

 to about 30 inches. Beyond this point it seems to fall off slightly, 

 probably because of declining vigor. Unfortunately, sufficient data 

 are not available to compare blackjacks of various diameters. Ob- 

 servations indicate that the trees below an approximate limit of 20 

 inches are relatively ineffective seed producers. This is not due 

 wholly to immaturity, but also to the fact that, even after cutting, 

 trees below this size are often dominated by older ones. The great 

 majority of blackjacks occur in groups of considerable size. Under 

 these conditions cones are borne in appreciable quantities only at 

 the tips of branches which are exposed to sunlight. Germination 

 tests have, as a rule, given somewhat higher values for blackjack 

 than for yellow pine, although 1913 was an exception. 



The average yields in 1909 and 1913, as shown by Table 5, were 

 1.61 pounds for yellow pine and 1.06 pounds for blackjack. These 

 yields apply to normal trees above 11 inches in diameter in virgin 

 stands. The question immediately arises as to whether they apply 

 to stands after cutting. Removing trees of poor crown development 

 and giving more sunlight to those left would tend to raise the aver- 

 age production. This is undoubtedly true of yellow pine, because 

 all the trees of this class which are left are selected with special 

 reference to crown development. Blackjack, however, is left, re- 

 gardless of crown development, excepting for the removal of diseased 

 or defective specimens. Blackjacks benefit from the elimination of 

 root competition and to some extent from the removal of the shade 

 cast by older trees; but blackjack groups are not, as a rule, opened 

 up sufficiently to influence seed production. 



YIELD OF SEED IX CUT-OVEE STANDS. 



Investigation of the method followed in gathering the data in 

 1909 and 1913 reveals the fact that cones were collected only from 

 such trees as promised a sufficient yield to justify the work. This 

 applies especially to the 1909 collection. Thus, the trees bearing no 

 cones or very small quantities are not represented, and. therefore, 

 an average for all trees as they occur in a stand would be lower than 

 the above figures. In 1913 a survey by Krauch of an area logged 

 the same year under Forest Service supervision showed that out of 

 a total of 761 trees 12 inches and over in diameter, the respective 

 percentages classed by ocular estimate as bearing good, light, and no 

 seed crop were 38, 25, and 37. In other words, although the crop 



