Seed Production and Dissemination
The cones of black spruce remain partially closed and disperse seed for several years, providing an adequate supply of seeds to reproduce the stand whenever fire occurs. Both the number and viability of the seeds decline rapidly, but some viable seeds may remain in the cones for as long as 25 years (15). In Minnesota, 1-year-old cones contained an average of 50 seeds; 7-year-old cones, 10 seeds; and 19-year-old cones, only 1 or 2 seeds (50). In Newfoundland, the number of seeds per cone was greatly reduced in 4 years (3.7 seeds per cone), but seed germination remained high (above 90 percent) for 12 years and then declined rapidly in older seeds (44).
Black spruce seeds are dispersed throughout the year, but dispersal is highest in the spring and lowest in the fall (16). Fires open the cones and accelerate seed fall for periods of 60 days (55) to 2 to 3 years; the effect apparently varies with fire intensity.
The average annual seedfall is about 490,000/ha (200,000/acre) for Minnesota (26) and substantially higher for Ontario- 2,450,000 to 4,180,000/ha (990,000 to 1,692,000/acre) (15). A maximum of 12,720,000 seeds per hectare (5,148,000/acre) has been reported from Ontario (29). In northern areas, even near tree line, amounts of seed are within the range of those from southern areas, with annual amounts from 590,000 to 1,300,000/ha (240,000 to 528,000/acre) reported from Inuvik in Northwest Territories (6) and 850,000/ha (344,000/acre) from central Alaska (49).
Black spruce has the smallest seed produced by any spruce in North America, averaging 890,000/kg (404,000/lb). Despite their light weight and relatively large wings, the seeds are not commonly dispersed over long distances. Seed dispersal, primarily by wind, is effective up to 79 m (260 ft) from the windward edge of a mature stand (27).
- Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp. http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm
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