Temporal variations in the understory photosynthetic photon flux density of deciduous stand: the effects of canopy development, solar elevation, and sky conditions

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2001

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  • handle:  10670/1.9ghh24
  • Gendron, F.; Messier, C. et Comeau, P.G. (2001). « Temporal variations in the understory photosynthetic photon flux density of deciduous stand: the effects of canopy development, solar elevation, and sky conditions ». Agricultural and Forest Meteorology, 106, pp. 23-40.
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F. Gendron et al., « Temporal variations in the understory photosynthetic photon flux density of deciduous stand: the effects of canopy development, solar elevation, and sky conditions », UQAM Archipel : articles scientifiques, ID : 10670/1.9ghh24


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The effects of canopy development, solar elevation, and sky conditions on temporal variation in photosynthetic photon flux density (PPFD) were examined within a 9-year-old bigleaf maple stand on Vancouver Island (Canada). PPFD was measured every second and stored as 10-min averages from 18 May to 14 October 1996, at 52 microsites characterised according to their growing season %PPFD (GSP). PPFD and %PPFD variability was examined at three different temporal levels. Specific days in May, July, and September with clear and overcast sky conditions were selected to separate the effects of canopy development and solar elevation on diurnal and seasonal light variability. Diurnal light variability expressed as the mean of the difference between two consecutive 10-min averages of PPFD and %PPFD decreased with increasing GSP on clear days in May. For clear days in July and September, variability was characterised by arc-shaped relationships with high variability for microsites receiving between 20 and 80% GSP and lower variability for microsites below 20 and above 80% GSP. On overcast days, diurnal variability in PPFD increased with increasing GSP while diurnal variability in %PPFD showed an arc-shape relationship. The coefficient of variation of PPFD and %PPFD decreased with increasing GSP on clear days and sunflecks decreased with decreasing GSP and from May to September. Day-to-day light variability expressed as the mean difference between consecutive daily PPFD increased with increasing GSP while the mean difference between consecutive daily %PPFD was higher for microsites receiving between 20 and 80% GSP. The coefficient of variation for the daily PPFD and %PPFD was higher for microsites receiving

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