10 BULLETIN 1105, U. S. DEPARTMENT OF AGRICULTURE. 



during the past 12 years has deferred germination been observed. 

 In the summer of 1912 several plots were heavily seeded artificially 

 with western yellow pine. The summer rains of that season were 

 unusually light and irregular, with the result that on plots which 

 had received little or no soil preparation very few seedlings ap- 

 peared. A number of small plots were screened to exclude rodents. 

 During the summer of 1913, when the rains were abundant, seed- 

 lings sprang up on these plots in such numbers as to prove beyond a 

 doubt that the majority must have come from seed which failed to 

 germinate the preceding season. 



AMOUNT OF SEED REQUIRED. 



Studies aiming at a quantitative determination of the amount of 

 seed required to secure a satisfactory stand of seedlings have not 

 succeeded in fixing absolute standards, because of the extreme varia- 

 tions encountered on different sites and in different seasons. The 

 greatest variable is rainfall. In unfavorable years no amount of 

 seed will bring results. In seasons when growing conditions are 

 normal or above normal, germination is good if seed is present, and 

 usually there is some survival. 



One of the most direct and obvious factors in seed supply is the 

 consumption of seed by rodents. The effective seed supply is that 

 which is preserved until moisture and temperature conditions are 

 such that germination can take place. In years of light seed produc- 

 tion chipmunks and mice probably destroy almost the entire crop, 

 but in good seed years a considerable amount remains unconsumed. 

 This surplus is what counts in natural reproduction. It would be of 

 interest to know to what extent the number of seed-eating animals 

 fluctuates from year to year in relation to the pine-seed crop. It can 

 scarcely be assumed offhand that failure or near failure of the pine- 

 seed crop for two or more years will result in starvation of these 

 animals, since they undoubtedly find a considerable source of food in 

 the seeds of herbaceous plants. It does, however, seem safe to assume 

 that if large crops of pine seed were produced over an extensive 

 area annually, the seed-eating animals would increase to the limit 

 of the food supply, and that therefore the frequent occurrence of 

 short seed crops tends to hold these pests in check. 



In attempting to fix a minimum limit of seed requirement, it must 

 be borne in mind that in average years from 90 to 99 per cent of the 

 seeds will be lost either through failure to germinate or through in- 

 fant mortality. It is estimated that on the plots under observation 

 near the Fort Valley Experiment Station during the nine years 

 prior to the heavy seed crop of 1918, not more than one out of every 

 thousand germinable pine seeds produced a seedling which lived be- 

 yond the age of 5 years. Present indications are that the 1918 seed 





