REPBODITCTION OF WESTERN YELLOW PINE. 9 



FACTORS INFLUENCING REPRODUCTION. 



The problem of determining the effect of various factors upon re- 

 production has been a difficult one on the Coconino and Tusayan 

 National Forests, for the reason that reproduction has proceeded so 

 slowly and in such erratic fashion that relationships could not always 

 be clearly seen. Causes could be studied in detail, but with the 

 almost entire absence of positive, concrete effects the conclusions 

 which could be drawn become largely abstract, not to say purely 

 theoretical. Now that considerable numbers of seedlings have be- 

 come established under conditions which are pretty well known, the 

 problem is easier. 



Success or failure is more or less directly related to a number of 

 factors. These are (1) seed supply; (2) climate; (3) soil; (4) her- 

 baceous vegetation; (5) cutting; (6) brush disposal; (7) grazing; 

 (8) miscellaneous enemies, including fire, insects, and rodents. 



SEED SUPPLY. 



Although reproduction is dependent upon a great many conditions 

 other than seed supply, the presence of a sufficient amount of seed 

 properly distributed is an obvious prerequisite. Correlation of 

 available data on seed crops with ages of seedlings now on the 

 ground, for specific areas in the vicinity of the Fort Valley Experi- 

 ment Station, shows that abundance of reproduction is at least in a 

 broad way related to seed crops. (See Table 9.) As a rule, the 

 greatest number of seedlings on the basis of both germination and 

 survival originates from the heaviest seed crops. A notable ex- 

 ception was in 1909, when a good seed crop resulted in the establish- 

 ment of very few seedlings. Unfortunately, no quantitative records 

 of germination are available from 1910 to 1913. No germination 

 occurred in 1915, 1918, and 1920, following years of no seed pro- 

 duction. 



Ordinarily there is no deferred germination of western yellow 

 pine in this region; that is, germination almost invariably takes 

 place during July and August of the first suriimer after the seed 

 matures. This point is mentioned because in certain species, notably 

 Douglas fir and western white pine in the Northwest, according 

 to Hoffman {!£) the seed may lie dormant for years, thus accumu- 

 lating in large quantities which germinate when favorable con- 

 ditions arrive, especially after cutting. Western yellow pine seed 

 in the Southwest does not normally lie over, because under favor- 

 able conditions it germinates in from 10 to 20 days, and because 

 the occurrence of • summer rains, at a time when temperature is 

 favorable, creates almost ideal conditions for germination over a 

 continuous period lasting from 30 to 60 days. Only in one instance 



