REPRODUCTION OF WESTERN YELLOW PINE. 15 



In the absence of adequate data on yield, the solution of this prob- 

 lem has been approached by estimating the quantity of cones on the 

 ground. The bulk of the cones fall on a fairly regular area almost 

 directly under the crowns. (PL II.) The product of trees grow- 

 ing singly can readily be distinguished from that of their neighbors ; 

 but where several trees stand in a group the group must be treated 

 as a unit. Most accurate results can be obtained by counting all of 

 the cones on the ground; but since this procedure is very time- 

 consuming, an approximation obtained by counting the cones on 

 measured plots and thus calculating the number on the entire area 

 has been considered reliable enough for certain comparisons. If 

 the examination is made at the proper time, the cones of the latest 

 crop can be distinguished from those of previous ones; but if the 

 examination is delayed until all of the cones have become weathered, 

 confusion is likely to arise. In the latter case a count of all the 

 cones on the ground gives a comparison covering an indefinite 

 period of years. If data are available on the number of cones re- 

 quired to produce a pound of seed, cone yields may be converted 

 into seed yields. Since the factor varies in different years and for 

 different trees, it should be applied with a clear understanding of 

 its limitations. According to studies in 1913, the number of cones 

 required for a pound of seed is 326 for yellow pine and 325 for 

 blackjack. 



On a cut-over area about 20 miles south of Flagstaff it was deter- 

 mined by the method described above that from four to six blackjacks 

 above 11 inches diameter breast high, as they usually occur in groups, 

 are required to produce as much seed as a single free-standing yellow 

 pine. In one instance, which is fairly typical, there were 19 black- 

 jacks in a single group. The diameters were distributed as follows: 

 11 to 15 inches, 11 trees; 16 to 20 inches, 5 trees; 21 to 26 inches, 3 

 trees. An area of 4,600 square feet was covered by cones, and the total 

 number was calculated at 5.960, or an average of 314 per tree. Judg- 

 ing by the relative density of cone litter under various trees, it is 

 evident that fully half of the total cone production of this group 

 should be credited to about four of the largest trees. No attempt 

 was made to separate the last crop (1918) from preceding ones. A 

 good crop is known to have been borne in 1913, but only two light 

 crops occurred between 1913 and 1918. It is believed that all the 

 cones antedating 1913 and probably most of the 1913 crop were 

 eliminated by decay. 



About 200 feet from the above group was a single yellow pine 30 

 inches in diameter and of good crown development. A survey of the 

 cone litter gave a total of 1,950 cones for the same period as that in- 

 volved above. In other words, this tree produced as many cones as 6.2 

 blackjacks from 1913 to 1918. 



