Summary1 Seed germination in light and dark, and responses to irradiance and light quality, were tested in shadehouse experiments for 19 West African tropical forest tree species representing a wide range of ecological types. Germination in forest gaps of dierent size was tested for 11 species. 2 Percentage germination was reduced in the dark only for three small-seeded species that are common in forest soil seed banks: Musanga cecropioides, Nauclea diderrichii and Milicia excelsa. Percentage germination of the other 16 species, including four widely regarded as`pioneers', was unaected. 3 Eects of dierent irradiances in shadehouses, where the seeds were watered, were signi®cant for some species, but there was no consistent pattern. Irradiance eects in forest gaps, where the seeds received only natural wet season rainfall, were more widespread and substantial, and were most commonly shown as a depression of percentage germination at high irradiance. 4 Eects of light quality (neutral vs. green shade; red : far-red = 0.43) were insignificant at 5% irradiance in shadehouses for all species except Nauclea diderrichii. In growth chamber experiments, the low energy response was only evident at 1.0 mmol m ±2 s ±1 (< 1% of unshaded forest irradiance) in Musanga and Nauclea. 5 The speed of germination was aected by irradiance in many species, but the eect was small compared with dierences between species, in which time to complete germination varied between 3 weeks and over 6 months. 6 Seeds of Ceiba pentandra and Pericopsis elata planted in deep forest shade (2% irradiance) and in a small gap (30% irradiance) germinated well in both sites, showed exponential biomass growth in the gap but a linear decline in mean seedling biomass and subsequent death in deep shade. 7 Light-mediated germination is relatively rare among these forest trees, even among pioneers, so that the working de®nition of a pioneer should be seen to depend more on a species' ability to survive in forest shade. The eects of canopy opening on seed germination are small except in the largest openings, which severely depress germination in a number of species, including some species with strongly light-demanding seedlings.
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