51.
Annual production rates of reproductive organs in
Fagus crenata forests in the lower area of the species' range were studied using 10 litter traps in 1980–1986. The production rates of
dispersed pollen were estimated by multiplying the number of fallen male inflorescences per ha per year by the mean amount
of pollen per inflorescence before anthesis. Large annual fluctuations in the production rates of male and female inflorescences
were recognized, whereas their annual trends were synchronized with each other. Pollen production rates were within the range
1.0–6900 (mean: 1630)×10
9ha
−1 yr
−1, the maximum/minimum ratio attaining 7000.
F. crenata was the lowest producer of pollen among seven tree species studied: the number of pollen grains equivalent to a single ovule
was in the range 6.0–14×10
4. Furthermore, the mean dry weight of a single pollen grain (3.77×10
−5mg) was higher than for wind-pollinated species. Three factors seemed to cause the low seed fertility of
F. crenata. The dry-matter production rate in the best seed year reached 3252 kg ha
−1 yr
−1, of which pollen accounted for 259 kg ha
−1 yr
−1. Unproductive years with less than 10% of the maximum production occurred four times in a 7-yr period. In such years there
were fewer male and female inflorescences, and more fruit dropped as a result of insect damage. Lower nut dissemination would
play an important role in suppressing any increase in nut predators, and fewer flowers would be produced to avoid wastage
of photosynthates in a cool-temperate climate.
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