20 



CIRCULAR 791, U. S. DEPARTMENT OF AGRICULTURE 



CONDITIONS AFFECTING REGENERATION 



The ease and certainty with which a species regenerates are con- 

 siderations of paramount importance in forest management. Hence, 

 the ability of black spruce to reproduce and the requirements control- 

 ling reproduction have been studied in detail. 



Seed Supply and Dissemination 



The seeds in black spruce cones in the absence of fire are not all freed 

 for 2 or 3 years after ripening 16 (IS). It has been established by 

 means of seed trap collections that during this period the seeds are 

 disseminated slowly throughout practically the entire year (table 4). 

 This slow rate of dissemination has the effect of assuring that a con- 

 siderable amount of freshly deposited seed is almost always present 

 on the ground. It also provides for some scattering of seed practically 

 every year regardless of the success of the current seed crop. The 

 annual seed fall for a 5-year period in an upland stand is shown 

 below. Comparison of these data with those on seed production (table 

 2, column 2, upland stand, p. 16) shows that there was substantially 

 less fluctuation in annual seed fall than in annual seed production. 



Year 



Seeds per 



acre, 



number 



August 1. 1934- July 31, 1935 286, 222 



August 1, 1935-July 31, 1936 198, 224 



August 1, 1936-July 31, 1937 - 439, 110 



August 1, 1937-July 31, 1938 265,312 



August 1, 1938-July 31, 1939 — 227,328 



Table 4. — Black spruce seed fall in upland and sivamp stands, by 

 months, in northeastern Minnesota 



Period 



Average fall of seeds per acre 



Upland 



Swamps 



August 



September 



October to April and monthly average 



May 



June 



July 



Total 



Number 



21, 602 



44, 998 



130, 151 



(18, 593) 



42, 486 



43, 590 

 30, 262 



313, 089 



Percent 

 7 

 14 

 41 



14 

 14 

 10 



Number 

 16, 050 

 36, 483 

 71, 433 



(10, 205) 

 24, 067 

 26, 667 

 13,017 



100 



187, 717 



Percent 



9 



19 



38 



13 



14 



7 



100 



1 Basis, 33 seed traps 3.3 feet square, for periods of 3 to 5 years. Two germi- 

 nation tests with different lots of seed both showed a viability of 31 percent. 



Undoubtedly some black spruce seeds are carried by the wind or 

 driven along the surface of hard-packed snow for considerable dis- 

 tances, but the great majority of them come to rest surprisingly close 



See footnote 13, p. 15. 



