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|Title: ||E ect of light on the germination of forest trees in Ghana|
|Authors: ||KYEREH, Boateng|
SWAINE, M. D.
red : far-red ratio
|Issue Date: ||1999|
|Publisher: ||Journal of Ecology|
|Abstract: ||1 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 spe-
cies representing a wide range of ecological types. Germination in forest gaps of
di erent size was tested for 11 species.
2 Percentage germination was reduced in the dark only for three small-seeded spe-
cies 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 una ected.
3 E ects of di erent irradiances in shadehouses, where the seeds were watered,
were signi®cant for some species, but there was no consistent pattern. Irradiance
e ects 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 E ects of light quality (neutral vs. green shade; red : far-red=0.43) were insignif-
icant 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 a ected by irradiance in many species, but the
e ect was small compared with di erences between species, in which time to com-
plete germination varied between 3 weeks and over 6months.
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 seed-
ling 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 e ects 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.|
|Description: ||This article is published in Journal of
|Appears in Collections:||College of Agric and Natural Resources|
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