HEPRODUGTIOISI' OP WESTERN YELLOW PINE. 21 



Records for other areas in the same vicinity are similar to, though 

 not identical with, those in Table 9. When a good seed crop occurs 

 generally over a region there is usually some seed everywhere, but 

 the yield is likely to be much heavier on some specific areas than on 

 others. This relation was strikingly brought to the author's atten- 

 tion in 1919, when the open cones of the hea^^^ crop of 1918 still 

 remained on the trees or were readily distinguishable on the ground.^ 

 In the region west and a few miles north of the Fort Valley Experi- 

 ment Station the crop was the heaviest within the memory of forest 

 officers in this region. Only 2 miles east of the station, however, 

 the yield was very noticeably lighter. About 3 miles north, ap- 

 proaching the San Francisco Mountains and the upper limits of the 

 yellow-pine type, the production was classed as light. South and 

 southeast of Flagstaff it ranged from fair to good, but west and 

 southwest it was heavy. In the cinder region, about 15 miles east 

 of Fort Valley, the crop was very light. In 1920 practically no cones 

 were in. evidence in the region west of Fort Valley, where heavy 

 yields were recorded in 1918 ; but in the cinder region east of Flag- 

 staff, where only a very light crop was recorded in 1918, a fairly good 

 crop occurred in 1920. 



In some instances it is possible to account for these variations. It 

 is known, for instance, that cone weevils figured prominently in the 

 failure of the seed crop in the cinder region in 1918. The same pest 

 cut down the yield materially in this locality in 1920. The light pro- 

 duction in the extreme upper limits of the yellow-pine type in 1918 

 might be accounted for by temperature conditions. Cutting is also 

 believed to be a factor. The young trees left on cut-over areas 

 respond to the effects of increased light and root space, but increased 

 seed production apparently does not take place until about five years 

 have elapsed. In a number of instances marked variations in seed 

 production are noted in the absence of apparent differences of any 

 kind. 



European foresters have found that seed production follows fairly 

 well-defined laws of periodicity. Records for yellow pine on the 

 Coconino and Tusayan, although they are not long enough to provide 

 a reliable basis, indicate that good seed crops occur rather generally 

 every three to five years. During the intervening period one or two 

 light crops and about the same number of complete failures may 

 be expected. It is believed that the long period between good seed 

 crops may be clue to circumstances not connected with the fruiting 

 habits of the tree. Repeated observations have shown that enormous 

 numbers of cones die during the first, season. Leiberg {IJi) attributes 

 this to desiccation by the hot, dry winds which sweep this region 

 during May and June. He also calls attention to inadequate f ertili- 



^ Few cones fall until the second season following maturity. 



