REPRODUCTION OF WESTERN YELLOW PINE. 17 



all sound, healthy blackjacks, aside from a few removed in thin- 

 nings, and in addition as many yellow pines as are needed to insure 

 adequate seed production. If 8 blackjacks are left. 2 yellow pines 

 will complete the seed requirements: if only 1 blackjacks are 

 left. 3 yellow pines are needed. It will probably be necessary to 

 modify this scheme to meet special conditions. Thus, when all the 

 blackjacks are small, say below 15 inches in diameter, and closely 

 grouped, the number of yellow pines should be increased. If the 

 blackjacks are large and in open arrangement, the number of yellow 

 pines might be decreased. It is suggested, as a tentative rule, that 

 when the blackjacks over 20 inches in diameter exceed three per 

 acre, those in excess of this number be classed ( from the stand- 

 point of seed production) as yellow pine. 



Foresters of long experience with western yellow pine stands have 

 observed that some trees seem to be naturally more prolific than 

 others of similar size and external characteristics. Good seed 

 bearers are recognized by the presence of great accumulations of 

 old cones around their bases. Often the remains of three or four 

 good cone crops can be identified. Absence of either old or recent 

 cones is taken as an indication of low productiveness. In order to 

 check these observations, the seed records of several sample plots 

 have been examined. On four plots near the Fort Valley Experiment 

 Station, an ocular estimate of the see ' crop for each tree has been 

 recorded annually since 1912. About ;00 trees are included in this 

 record. During these nine years many of the larger trees have 

 produced four good cone crops, while other trees of similar size and 

 development have p. duced no good crops. In many instances the 

 difference in production can be accounted for by a difference in ex- 

 posure to sunlight, or the presence of disease or injuries, but often 

 no differences of this kind are apparent. In making these compari- 

 sons, only trees of apparently good vigor, good exposure to sunlight, 

 and of a diameter above 20 inches have been considered. The high 

 diameter limit was adopted with the idea of excluding trees which 

 may not have come into full bearing on account of immaturity. 

 On Plot 3a. out of a total of 59 trees falling within the above specifi- 

 cations, IT per cent have produced four good crops. 20 per cent three. 

 29 per cent two. 20 per cent only one. and 11 per cent have borne no 

 good cone crops during the nine years from 1913 to 1921. inclusive. 

 The other plots show a similar relationship. 



Table 7 shows the individual records of a number of representative 



trees on Plot 3a. A similar table could be prepared for each of the 



other plots. These records point unmistakably to the existence of 



individual variation. A longer period of observations might show 



904°— 23 2 



