Flowering, seed production, and germination of green alder (Alnus viridis ssp. crispa (Aiton) Turrill) were studied in populations north of Lake Superior. Anthesis and fertilization took place from mid-May to early June. Aboutone-third of the lateral buds contained female catkins, and an average of 60% of these catkins were fertilized and bore some seed. A high percentage of seed had abnormal, nonviable embryos. There was wide variation in flowering and seed characteristics among clumps of alder. Reproductive features of individual clumps were not correlated from year to year, suggesting an alternate bearing pattern in which some clumps were productive in any given year. Annual seed rain in individual understory alder stands varied from 0.14 to 2.40 million per hectare. At dispersal seeds exhibited conditional dormancy, which allowed germination at higher temperatures under a long photoperiod. Capacity for germination under a wider range of environments was facilitated by stratification.
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Farmer et al. (1985) studied this question.