10 



are usualh' old and consequently of large size. The average diam- 

 eter of the healthy yellow pine in this study is only 23 inches, against 

 27 inches for those affected by heart rot. It is probable that, as in 

 the case of germination, the rot ordinarily has no material effect. 



Sjpike tops show a yield only one-lialj as great as that given for healthy 

 yellow pines. This is probably due to a reduction in the size of the 

 living croA^Ti. The living branches of spike tops are frequently 

 heavily laden with cones, and it is probable that the injury causuig 

 the death of the top acts as a stimulus upon cone production, as 

 upon the vitality of the seeds. 



The influence oj hasal hums upon yield is not jully demonstrated. 

 The 3"ellow pine bearmg fire scars shows an average yield of 0.3 

 bushel more than the healthy yellow pine; but a comparison of 

 diameters shows that the scarred trees have an average diameter 

 of 25 inches against 23 mches for the healthy ones. Wliether the 

 greater yield is due entirely to the greater size of the burned trees 

 or whether the influence of the burns is also a factor, can not be 

 determined from the data at hand. 



The yield' of trees suffering from suppression and attacks of harTc 

 beetle and mistletoe are all much helow that of normal trees of their 

 class. Wliile the number of trees in each case is too small to furnish 

 reliable data, the results are very significant. 



The yield decreases as the density of the stand increases. The aver- 

 age yield of cones per tree for open, medium, and dense stands are 

 1.8, 1.1, and 0.7 bushels, respectively. This difference is undoubtedly 

 due mainly to a difference in crown development as influenced by 

 gro^\ing space. Since western yellow pine is very light demanding, 

 the trees growing in close stands have narrow, short crowns, and 

 only those branches which are exposed to full or nearly full sunlight 

 bear any cones whatever. Therefore, although the seed produced 

 b}" a tree in a close stand is of higher quality than that produced in 

 the open, as indicated by the germmation tests, the total seed- 

 producing capacity of a tree in a close stand is much lower. 



APPLICATION OF CONCLUSIONS. 



Blackjacks are the most desirable trees to leave for regeneration 

 in cutting. The blackjack has the advantage over the older yellow 

 pine in point of seed quality, and also in the rate of growth. A black- 

 jack left for a future cutting will increase rapidly in volume, whUe 

 a yellow pine will increase but slowly or even deteriorate. 



In marking for cutting in the yellow-pine type it is the invariable 

 practice to leave all healthy blackjacks, and also to leave a suffi- 

 cient number of yellow pmes to insure a second cut in about 30 to 

 50 years. But if a second cut w^ere the only consideration in mark- 

 ing there would not always be sufficient provision made for seed 



[Cir. 190] 



