REPRODUCTION OE WESTERN YELLOW PINE. 6 



In addition to insuring an adequate seed supply, it was considered 

 important to retain trees enough to preserve forest conditions, since 

 excessive opening up of the stand results in increased danger from 

 wind, evaporation, and frost. 3 Recent studies have thrown much 

 additional light on this phase of the problem. 



Failure of reproduction was shown to be due less to poor germi- 

 nation than to high mortality during the first two or three years fol- 

 lowing germination. The high death rate among seedlings less than 

 a year old was attributed largely to the fact that germination does 

 not. as a rule, take place until July or August, and consequently tbe 

 seedlings ill very tender at the end of the growing season. 



Records show that great numbers succumb^as a result of droughts in 

 September and October, that some are killed by early frosts, and 

 that many are thrown out of the ground by frost heaving, which 

 takes place late in the fall and early in the spring. Drought was 

 found to take an additional toll in the dry foresummer of the second 

 and third seasons. 



The presence of brush and litter resulting from logging, if prop- 

 erly distributed, was foimd to favor reproduction by protecting 

 young seedlings against drought and frost. Studies in 1920 have 

 shown that this conclusion applies only under certain conditions. 



Reproduction was observed to be better on the more or less gravelly 

 or stony soils than on heavy clay soils which are largely free from 

 gravel and stones. This was thought to be due to the greater per- 

 meability to moisture and plant roots resulting from the admixture 

 of coarse materials. 



Two insects, the tip moth and the white grub, or larva of the May 

 beetle, were charged with an enormous amount of damage. 



Examinations as early as 1908 showed excessive damage by sheep 

 and indicated the advisability of excluding them during the period 

 of reproduction. The conclusions were later corroborated by the 

 more comprehensive study of Hill (11). whose investigation showed 

 considerable variation in the amount of damage for different ages 

 of seedlings, season and intensity of grazing, and character of for- 

 age. His work is more fully discussed in the chapter on grazing. 



SUMMARY OF CONCLUSIONS IN STUDY UP TO 1918. 



The status of the reproduction problem and the outlook on the 

 Coconino and Tusayan Xational Forests, as viewed by the writer (18) 

 in 1918, may be briefly stated as follows: 



Adverse climatic conditions dominate the situation to such an extent 

 that no system of silviculture can hope completely to solve the repro- 

 duction problem in this region. Dense, even-aged stands of seedlings 



8 Similar observations had been made by Plummer (20) in 1904. 



